Flow meter insert for a drip chamber

Abstract

A flow meter insert (10) for a drip chamber for intravenous administration, comprising a main liquid flow channel having an inlet passage (11), an outlet (13) and a flow resistance passage (12) comprising an orifice. A flow indication channel (14) is in communication with the main liquid flow channel. The flow resistance passage and the flow indication channel are defined by a first recess / channel (10r). The flow resistance passage and the flow indication channel are located between the insert and a wall of the drip chamber. The orifice of the flow resistance passage creates a resistance to liquid flow, forcing liquid into the flow indication channel. The liquid level in the flow indication channel is proportional to the liquid flow rate through the main liquid flow channel. The orifice is defined by a first face parallel to a plane defined by the orifice and a second face at an angle of 20-55° to the plane of the orifice.

Description

Technical Field

[0001] This invention generally relates to flow meter devices and / or components thereof suitable for intravenous administration of solutions. In particular, but not exclusively, the invention relates to a flow metering insert for a drip chamber for intravenous administration, a flow meter device including the insert, and an intravenous administration kit including the insert. Background Technology

[0002] Intravenous (IV) drug delivery systems are commonly used to administer various types of injectable solutions into a patient. IV drug delivery systems provide a means of controlling the aseptic flow of fluids (such as saline, glucose solutions, etc.) from a rigid or flexible supply container (such as an IV bag) into the patient's body. Traditional IV drug delivery systems are characterized by a closed chamber (so-called a drip chamber) with a nozzle outlet that produces droplets as the fluid flows. The purpose of the drip chamber is to calculate the fluid flow rate by counting the number of droplets per unit time. This can be time-consuming and inaccurate because the droplet size is not constant, and converting droplet timing into fluid flow rate can be difficult. Many well-established flow meter designs have been developed for IV fluid delivery.

[0003] A variation of a well-known rotor flowmeter design (such as US3587313A) employs a small ball of appropriate specific gravity (typically larger than the liquid, although in some designs it can also be a float) within a vertically arranged conical indicating chamber (or tube), with the liquid inlet located at the lower, smaller end of the chamber. As the liquid flows around the ball, it is pushed towards the larger cross-sectional area of ​​the indicating chamber, thus the ball's position indicates the liquid flow velocity. While these devices allow for more precise regulation and adjustment of flow rates, they are expensive to manufacture due to the required high tolerances and potentially complex component assembly.

[0004] Another type of flow meter device is the reverse flow type, such as that disclosed in US2479786A. The device in US2479786A employs a vertically arranged tube with a liquid inlet at the top and a short section at the bottom that bends backward to form an upwardly extending section (indicating chamber / tube) with an opening at its upper end. This arrangement is enclosed within a larger sealed housing (i.e., the drip chamber), which has an outlet to other tubing leading to the patient. Small orifices in the tube wall at the bends allow liquid to flow downward from the inlet into the drip chamber. The liquid flow, combined with the flow resistance caused by the orifices, causes the liquid level in the upward section to rise to a level proportional to the flow rate, thus serving as the indicating chamber / indicating tube. This design is simpler than a variant of a rotameter, but it is inaccurate at low flow rates and is difficult to manufacture multiple units with consistent geometry, further impacting calibration and accuracy.

[0005] The device in US4136692A uses a similar principle to US2479786A, replacing the bend with two chambers / tubes (an inlet chamber and an indicator chamber) connected to each other at their lower ends and enclosed within a larger sealed housing (the drip chamber) with an outlet to the patient. The small orifice in US2479786A is replaced by a highly precise orifice plate with a minimum thickness (approximately 0.001 inches or 0.0254 mm). This is intended to minimize any impact of temperature and viscosity variations on measurement accuracy; however, the design remains a relatively complex assembly of small parts, resulting in higher manufacturing costs compared to standard IV delivery systems.

[0006] Another variation of the countercurrent design is disclosed in US4291693A, in which the orifice plate of US4136692A is replaced by a flow restrictor, wherein at least a portion of the flow restrictor is oriented such that liquid passing through it moves upward to help avoid trapping any air bubbles. Similar to US4136692A and US2479786A, the flow resistance caused by the flow restrictor causes the liquid level in the upward indicator tube to rise to a level proportional to the flow rate. However, like the device in US4136692A, the design remains relatively complex, resulting in higher manufacturing costs.

[0007] US4523464A discloses another variation of a reverse-flow type device, which can be made of a thermoplastic material. Specifically, the device includes a flow-limiting orifice located at the lower end of a vertical inlet pipe and an indicating chamber, but the walls of the inlet pipe and / or the indicating chamber are formed by the walls of a closed housing. Compared to US4136692A and US4291693A, this device is relatively simple to manufacture; however, it still requires the assembly and welding of several component parts. Furthermore, it is less suitable for sudden changes in flow rate and is designed to measure the flow rate of liquid through a partially filled pipe, where the inlet pipe is supplied by gravity.

[0008] The applicant's prior patent EP3294379B1 discloses another variation of a reverse-flow type device, in which the flow meter device is formed from two separately molded parts, which can be easily assembled by fitting one part into the other. The first part includes a drip chamber, the second part includes an inlet tube, and when assembled, a generally U-shaped flow-limiting path and an indicating chamber are formed between the first and second parts. Although simple to manufacture and assemble, it still requires molding two custom parts.

[0009] The object of this invention is to provide an improved flow meter device that is easier to manufacture and assemble and more reliable than previous reverse flow type designs, while being cost-comparable to standard IV dosing systems based on droplet counting, and simpler, faster and more accurate to use.

[0010] The aspects and embodiments of the present invention were designed with the foregoing in mind. Summary of the Invention

[0011] According to a first aspect of the invention, a flow metering insert is provided for use with a drip chamber, for example, for intravenous (IV) fluid administration. The insert may include a main fluid flow channel and a flow indicator channel. The main fluid flow channel may include an inlet passage, an outlet, and a flow resistance passage located between the inlet passage and the outlet. The inlet passage may be connected to a fluid source, such as a fluid container or intravenous bag, for receiving the fluid flow. The flow indicator channel may communicate with the main fluid flow channel between the inlet passage and the flow resistance passage. The flow resistance passage provides resistance to the fluid flow therethrough, forcing the fluid into the flow indicator channel and reaching a level or height proportional to the rate at which the fluid flows through the main fluid flow channel, the inlet passage, and / or the flow resistance passage.

[0012] A flow resistance path may include an orifice. The orifice may be defined by a first surface and a second surface. The first surface may be parallel to the plane defined by the orifice. In use, when liquid passes through the orifice, the liquid flows from the first surface to the second surface; that is, in the liquid flow, the first surface is upstream and the second surface is downstream.

[0013] The second surface can be at an angle between 20° and 55° relative to the orifice plane. The second surface can be at an angle between 25° and 50° relative to the orifice plane. The second surface can be at an angle between 26° and 49° relative to the orifice plane, or an angle between 26° and 47° relative to the orifice plane. The second surface can be at an angle between 30° and 45° relative to the orifice plane. The second surface can be at an angle between 31° and 44° relative to the orifice plane, or an angle between 32° and 43° relative to the orifice plane, or an angle between 33° and 43° relative to the orifice plane.

[0014] The flow resistance path may include a second orifice. The second orifice may be defined by a first surface and a second surface. The first surface may be parallel to the plane defined by the second orifice. In use, when liquid passes through the orifice, the liquid flows from the first surface to the second surface; that is, in the liquid flow, the first surface is upstream and the second surface is downstream. The second surface may form an angle between 20° and 55° relative to the plane of the second orifice. Alternatively, the second surface may form an angle between 25° and 50° relative to the plane of the second orifice. Or, the second surface may form an angle between 30° and 45° relative to the plane of the second orifice.

[0015] An inserter can be used with and inserted into a drip chamber, including transparent drip chambers known in the art, such as drip or infusion devices for drug and / or intravenous (IV) administration, to form a flow meter device. Such drip chambers typically have a smooth inner surface. In particular, the inserter can be inserted into the upper part of the drip chamber, for example, through an opening at its apex. The drip chamber can be substantially rigid or flexible. Therefore, the fluid level or height in the flow indication channel can be observed through the sidewalls / outer wall of the drip chamber. A cap or lid with a device for connecting the flow meter device to a fluid source (e.g., an intravenous bag or container) (e.g., a standard ventilated or non-ventilated puncture device known in the art) can be attached to the drip chamber to close and seal the drip chamber and define a fluid flow path from the fluid source to the inlet passage of the inserter. In some drip chambers, a cap or lid may be integral with the drip chamber. For example, in a two-part drip chamber comprising an upper (e.g., with a puncture device) and a lower part, the upper and lower parts may be attached to each other to close and seal the drip chamber, and an insert may be inserted into the upper part through an opening at its lower end. Standard tubing, fittings, and / or flow controllers can be used downstream of the resulting flow meter device. When inserted into the drip chamber and connected to a liquid source, the flow indication channel of the insert provides a visual indication of the liquid flow rate, which is more direct, accurate, and reliable than methods based on counting droplets in other standard drip chambers without such an insert. Therefore, this insert can be retrofitted into existing standard IV drug delivery systems to provide improved flow metering with minimal cost and / or impact on standard IV drug delivery device manufacturing practices. Furthermore, according to ISO-8536-4 (an international standard requiring that droplets in medical gravity infusion devices must be continuously visible), the outlet of the insert can include a droplet-forming orifice so that the droplet flow from the outlet is still visible in the lower part of the droplet chamber as the liquid leaves the insert. The resulting flowmeter device can be "pre-charged" in the same manner as existing infusion devices, which involves squeezing and releasing the flexible lower part of the droplet chamber (below the insert) to draw liquid downward from the liquid source through the main liquid passage and expel air upward into the liquid source.

[0016] The main liquid flow channel and / or flow indication channel may be at least partially defined by the insert. The main liquid flow channel and / or flow indication channel may be partially defined by the insert such that when the insert is inserted into the drip chamber, the main liquid flow channel and / or flow indication channel are fully / sufficiently defined. Alternatively, the main liquid flow channel and / or flow indication channel may be fully defined by the insert or defined within the insert.

[0017] The inlet passage may be or include a closed channel. The flow resistance passage and / or flow indication passage may be at least partially defined by the insert. The insert may include one or more recesses and / or channels configured to at least partially define the flow resistance passage and the flow indication passage. The one or more recesses and / or channels may be one or more first recesses and / or first channels (relative to a second recess or second channel as defined below). The flow resistance passage and / or flow indication passage may be at least partially defined by one or more recesses and / or channels in the insert such that, when inserted into the drip chamber, the flow resistance passage and / or flow indication passage are formed or located between the insert and the wall (e.g., sidewall or outer wall) (inner surface) of the drip chamber.

[0018] Where the flow resistance passage and / or flow indication channel are partially defined by the insert, the flow resistance passage and / or flow indication channel may be or include one or more grooves or open channels formed in the surface of the insert. When the insert is inserted into the drip chamber, the one or more grooves or open channels may be closed, sealed, and / or completed by the (inner surface) of the walls (e.g., sidewalls or outer walls) of the drip chamber. This can greatly simplify manufacturing, thereby reducing the manufacturing cost of the insert. For example, it can be manufactured within standard injection molding tolerances and used with standard drip chambers that are widely available and used in the art.

[0019] The surface can be a mating surface and / or an outer surface of the insert (i.e., substantially opposite to the insert). The mating surface can be configured to mate with, i.e., contact / adjaculate and / or seal, the inner surface of the wall (e.g., sidewall or outer wall) of the drip chamber when the insert is inserted. The mating surface can be configured to conform to and / or contact the inner surface of the wall (e.g., sidewall or outer wall) of the drip chamber when the insert is inserted. The mating surface can be substantially smooth. Alternatively or additionally, the mating surface can be or include one or more sealing ribs extending around one or more recesses or open channels that partially define flow resistance pathways and / or flow indication pathways. The mating surface and / or one or more sealing ribs can be configured to at least partially deform the inner surface of the wall, and / or be at least partially deformed by the inner surface of the wall to form a liquid-tight seal between them.

[0020] When the flow resistance passage and / or flow indication channel are entirely defined by the insert, the flow resistance passage and / or flow indication channel can be or include one or more closed channels, such as those defined by one or more recesses and / or channels. This insert functions independently of the geometry of the drip chamber (since the flow resistance passage and / or flow indication channel are internal passages / channels of the insert) and therefore can be used with drip chambers of any shape, as long as the insert can be fitted into them. Alternatively, the insert itself can form a stand-alone flow meter device without needing to be inserted into the drip chamber. For example, where it is not necessary to form and observe droplets from the outlet, the insert can be connected in series with a liquid loop to monitor and / or set the flow rate through the liquid loop.

[0021] A liquid “channel” can refer to a closed channel, an open channel, or a channel in an insert having one or more open and closed channel portions. A closed channel is a channel having one or more channel walls that enclose the flow of liquid through it. An open channel is a channel in which at least a portion of the channel walls is open and exposed to its immediate surrounding environment, such that the flow of liquid through it is not completely enclosed (e.g., it can be formed by grooves).

[0022] The insert can be constructed, shaped, and / or sized to provide an interference fit within the drip chamber. Specifically, the insert can be configured to provide an interference fit shape and / or size between the mating surface and the wall of the drip chamber. This interference fit can provide a liquid-tight seal between the mating surface and the wall of the drip chamber to close and seal one or more recesses or open channels, and fully define or complete the flow resistance path and / or flow indication path. Therefore, no additional sealing and / or bonding of the insert to the inner surface of the drip chamber wall is required to provide a liquid-tight seal, which simplifies the assembly of the resulting flowmeter device.

[0023] The insert may be formed of or comprise a substantially rigid material. In this case, the insert may be provided with an interference fit within a substantially flexible / deformable portion of the drip chamber to provide a liquid-tight seal therebetween. Alternatively, the insert may be formed of or comprise a substantially flexible, deformable, and / or compressible material. In this case, the insert may be provided with an interference fit within a substantially rigid portion of the drip chamber to provide a liquid-tight seal therebetween. When the insert is formed of or comprises a substantially rigid material, the wall of the drip chamber may be substantially flexible or less rigid than the insert, such that when the insert is inserted into the drip chamber, the inner surface of the wall is at least partially bent or deformed to conform to the mating surface of the insert. Alternatively, when the insert is formed of or comprises a substantially deformable material, the wall of the drip chamber may be substantially rigid, such that the mating surface of the insert is at least partially deformed to conform to the inner surface of the sidewall. In either case, the mating surface is configured such that when the insert is inserted into the drip chamber, the mating surface can conform to (after deformation or no deformation) the final inner surface of the wall.

[0024] Inserts may be formed of or comprise thermoformed materials, such as plastics and / or thermoplastics. Example materials include, but are not limited to: acrylonitrile-butadiene-styrene (ABS) or equivalents, polyvinyl chloride (PVC) or non-PVC equivalents, polyethylene, polycarbonate, nylon, polypropylene, polyurethane, ethylene-vinyl acetate, or any plastic permitted for intravenous applications. ABS or equivalents may be suitable for forming substantially rigid inserts. PVC or non-PVC equivalents may be suitable for forming substantially flexible, deformable, and / or compressible inserts.

[0025] The flow meter device, including the insert, can be configured to be substantially vertical in use, allowing the liquid to flow downwards through the inlet passage under gravity. The terms "upper" and "lower" as used below refer to this direction.

[0026] The insert can have both length and width. The length can be in the longitudinal (vertical) direction / axis. This length can be in the insertion direction, which corresponds to the direction in which the insert is inserted into the drip chamber during assembly. The width can be in the transverse direction.

[0027] Although described above in the context of intravenous administration, the insert can also be used in series with other flow devices, such as electronic pumps, to monitor and / or set flow rates. Therefore, more generally, the insert can be used with and inserted into a liquid flow chamber or housing, which includes an opening for receiving the insert and an outlet for receiving liquid flow from the insert's outlet. The outlet can be located downstream of the insert's outlet. A flow meter device can be formed from the insert and the flow chamber or housing. The insert can be configured to close and / or seal the flow chamber or housing. Optionally, a cap or lid having a means for connecting the device to a liquid source can be used to close and seal the opening of the flow chamber or housing. Tubing, flow accessories, and / or flow controllers can be connected to the outlet of the flow chamber or housing or used downstream of that outlet. One or more filters, such as standard filters known and used in the art, can be included in the drip chamber, for example, at its bottom. A flow chamber or housing may include one or more walls (e.g., sidewalls or outer walls) defining an internal volume, cavity, or space sized to accommodate an insert. The walls may extend from the opening along the insertion direction. At least a portion of the walls of the flow chamber or housing may be substantially transparent, allowing the liquid level or height in the flow indication channel to be seen through the walls. The internal volume, cavity, or space of the flow chamber or housing may have a substantially circular horizontal cross-section (e.g., the interior of a drip chamber may be substantially cylindrical), or a non-circular and / or arbitrary horizontal cross-section. The inner surface of the walls may be tapered (inward) or non-tapered in the insertion direction. The flow chamber or housing may be substantially tubular. The flow chamber or housing may be or include tubes or tubular members. The flow chamber may be or include a container or bag having an opening, portions, and / or tubular sections configured to receive and / or accommodate an insert, such that the insert can provide a visual indication of the flow rate entering and / or passing through the container / bag / chamber. The exterior of the flow chamber or housing may have a regular or irregular shape. For example, this insert can be placed in a catheter bag to monitor the rate of urine expulsion. In other words, the geometry of the insert can be configured to fit many different flow chamber geometries and is not limited by the application.

[0028] Alternatively, where the flow resistance passage and / or flow indication channel are partially defined by the insert, a collar or ring may be used to close and / or seal one or more recesses or open channels. The collar or ring may extend at least partially around the insert and at least partially along the length of the insert. For example, when the insert is inserted into the collar or ring, or when the collar or ring is positioned at least partially around the insert, the flow resistance passage and / or flow indication channel may be formed between the insert and the (inner surface) of the wall (e.g., sidewall) of the collar or ring, as described above. The flow meter device may be formed solely of the insert and the collar / ring, or the insert and the collar / ring may be inserted into a drip chamber or flow chamber to form a flow meter device (in the latter case, the walls of the drip / flow chamber do not close and seal one or more recesses or open channels). Piping, flow accessories, and / or flow controllers may be connected downstream of the insert outlet / used downstream of the insert outlet.

[0029] The inlet passage of the insert may have an inlet end (upper end) and an outlet end (lower end). The upper end of the inlet passage may include an opening for receiving liquid flow.

[0030] The lower end of the inlet passage (outlet end) may communicate with one or more grooves or open channels in the outer / mating surface of the insert, which partially define the flow resistance passage and / or flow indication passage. The outlet of the insert may communicate with the flow resistance passage (outlet end).

[0031] The flow indication channel may include an inlet end that communicates with the outlet end of the inlet passage and the inlet end of the flow resistance passage. When the insert is arranged substantially vertically, the flow indication channel may extend substantially upward from its inlet end (lower end) to the open outlet end (upper end).

[0032] The operation / use of the insert relies on the principle that the liquid level / height in the flow indication channel is proportional to the liquid flow rate through the flow resistance passage. The change in liquid level / height with flow rate is determined by the flow resistance provided by the flow resistance passage. For example, for a given flow rate, higher flow resistance results in a higher liquid level / height in the flow indication channel. The flow indication channel may include a graduated scale to provide a visual measurement of the liquid level or height in the flow indication channel, thereby providing a measurement of the liquid flow rate through the flow resistance passage (and / or the inlet passage and / or the main liquid flow passage). The scale includes graduations or markings spaced at given intervals corresponding to a given flow rate range. A visible float may be provided for easy reading of the liquid level / height.

[0033] The insert may include a venting channel. The venting channel may be in fluid communication with the lower end / outlet end of the inlet passage, and is configured to expel any air bubbles in the liquid flow before it leaves the inlet passage and reaches the flow indication channel. The venting channel may have a lower end in fluid communication with the lower end / outlet end of the inlet passage and an open upper end. The lower end of the venting channel may be located upstream of the lower end of the flow indication channel. The venting channel may extend substantially parallel to and / or along the flow indication channel. The venting channel may extend in a direction substantially parallel to the longitudinal axis of the insert. When the insert is arranged substantially vertically, the venting channel may extend substantially vertically from its lower end. The venting channel is configured to allow any air bubbles in the liquid flowing out of the inlet passage to rise upwards in the venting channel without entering the flow indication channel, which would otherwise adversely affect flow measurement. The lower end of the venting channel may be positioned such that, in use, it is below a minimum liquid level defined by the liquid retained in the insert. The lower end of the venting channel may be positioned such that it is always submerged in use. This prevents the venting chamber from introducing air bubbles into the insert.

[0034] The venting passage can be configured such that, during use, liquid is forced into the venting passage and the indicating chamber, causing the liquid in the venting passage to reach the level or height in the indicating chamber. The relationship between the liquid level or height in the indicating chamber and the liquid level or height in the venting passage can be linear. The liquid level or height in the indicating chamber and the liquid level or height in the venting passage can be equal, causing them to rise and fall together. The liquid level or height in the indicating chamber and the liquid level or height in the venting passage may deviate due to the presence of air in the venting chamber.

[0035] The venting channel may include an orifice. This orifice provides an additional flow path for the liquid in the venting channel to travel to the outlet of the insert. The ratio between flow rate and liquid level changes when the liquid level is above and below the orifice.

[0036] The scale may include a first part and a second part. In the first part 62-1, the spacing between the marks may represent a first flow rate increment. In the second part, the marks may represent a second flow rate increment greater than the first flow rate increment. This makes the scale accurate and easy to read for liquid bolus administration. The flow rate increments represented by the marks on the scale may change at levels or heights above the liquid level in the flow indication channel corresponding to the height of the orifice in the exhaust channel.

[0037] The flow indicator channel can be substantially straight, curved, and / or include one or more curved sections. When the insert is arranged vertically, the flow indicator channel can extend substantially vertically from its inlet end. Optionally, when the insert is arranged substantially vertically (or at an angle to the longitudinal axis of the insert), at least a portion of the flow indicator channel can extend at an angle (non-zero angle) relative to the vertical direction from its inlet end. This angle can be in the range of approximately 5-85 degrees with respect to the vertical direction (or longitudinal axis), or 10-80 degrees, or 15-75 degrees, or 20-70 degrees, or 25-65 degrees, or 30-60 degrees, or 35-55 degrees, or any combination or subrange thereof. Tilting at least a portion of the flow indicator channel means that the vertical component of the scale is represented at an angle. This extends the vertical component of the scale over a greater distance (i.e., increases the absolute spacing / interval between a given scale / increment), which can make the level / height easier to measure / read and / or provide space for additional subscales, thereby increasing the resolution of the scale. This can be particularly useful at or near the inlet end of the flow indicator channel, where the liquid level / height corresponds to a low flow rate (e.g., below 50 ml / h). The flow indicator channel may be curved about the longitudinal axis of the insert and / or about the transverse axis of the insert. For example, the flow indicator channel may be curved away from the longitudinal axis, such as when viewed from the side of the insert. Angled flow indicator channels can also be curved (i.e., about the longitudinal axis of the insert) in cases where the inner surface of the drip chamber wall is curved (i.e., about the longitudinal axis of the insert), for example, it can be substantially helical. Angled and / or curved flow indicator channels can allow for a reduction in the length of the insert, for example, to accommodate flow / drip chambers with reduced dimensions.

[0038] The flow indication channel may include a first portion and a second portion arranged at different angles. The first portion may be the lower portion, which extends from the inlet end of the flow indication channel at an angle relative to the vertical direction (or longitudinal axis) when the insert is arranged substantially vertically, as described above. The second portion may be the upper portion, which extends substantially vertically from the first portion when the insert is arranged substantially vertically. Optionally, the second portion may extend from the first portion at an angle to the vertical direction (or longitudinal axis), wherein this angle is smaller than (i.e., closer to the vertical direction or longitudinal axis) the angle of the first portion / lower portion.

[0039] The change in liquid level or height in a flow indicator channel with respect to flow velocity can depend on the geometry and / or volume of the flow indicator channel. The smaller the volume, the faster the rate of change, and / or the faster the liquid level / height responds to changes in flow velocity, and vice versa.

[0040] Alternatively or additionally, one or more notches or openings may be formed in the wall of the flow indicating channel, configured to allow liquid to flow out of the flow indicating channel. When the liquid level in the flow indicating channel reaches the notch position and / or rises above the notch, some liquid can escape through the notch (entering the drip chamber). This means that a much higher flow rate is required for the liquid level in the flow indicating channel to continue rising above the notch position, as the rise in liquid level must also overcome the liquid loss through the notch. This provides a non-uniform scale, with higher flow sensitivity below the notch and lower flow sensitivity above the notch. In the case of more than one notch, each notch can be located at a different height in the flow indicating channel. This non-linear scaling may be ideal where higher flow measurement accuracy is required at lower flow rates, but the same flow meter must also measure high flow rates. In this case, a linear scale may be impractically large.

[0041] The flow resistance passage has a sufficient cross-section and / or length to provide the required flow resistance. The flow resistance passage can have a uniform or non-uniform width / cross-section for flow. The flow resistance passage may include an orifice. Using an orifice for throttling (rather than a long, narrow conduit / pipe section) can make the assembled flow meter device less sensitive to changes in liquid viscosity. The greater the resistance in the flow resistance passage provided by orifice throttling, the less sensitive the flow rate measurement is to changes in liquid viscosity. The greater the resistance provided by narrow pipe flow (e.g., in the case of long, narrow throttling), the more sensitive it is to changes in liquid viscosity. Therefore, preferably, the orifice is as short as possible in the flow direction (within the constraints of the manufacturing process). The wall of the recess or open channel that partially defines the flow resistance passage may include a protrusion pointing inward or extending into the passage or toward the center of the passage to narrow the width of the flow resistance passage. The protrusion may extend from the bottom of the recess and opposite the wall of the drip chamber. Additionally or alternatively, the protrusion may extend from the sidewall of the recess or flow resistance passage toward the opposite sidewall of the recess or flow resistance passage. The orifice can be formed by a single protrusion, for example, opposite a substantially straight portion of a wall (e.g., the wall of a groove or a drip chamber), or the orifice can be formed by two opposing protrusions. The cross-section of the protrusion can be substantially rectangular, V-shaped, or triangular. The angle θ of the sidewall forming the protrusion... v The sharper the orifice, the more ideal it becomes, and the less sensitive the flow meter device is to changes in liquid viscosity. The V-shaped protrusion represents a trade-off between performance and manufacturability.

[0042] When the flow rate through the flow resistance passage is substantially between 0 and 250 mL / h, the orifice width can provide sufficient resistance to the liquid flow, resulting in a discernible change in the liquid level / height in the flow indication chamber. If circular, the orifice can have a radius of substantially 0.5 mm, or, for non-uniform cross-sections, its size can provide an equal cross-sectional area. Optionally, the radius / size can be approximately 0.3 mm, 0.4 mm, 0.6 mm, or 0.7 mm.

[0043] The level / height in a flow indicator channel varies with the flow velocity through the flow resistance path, determined by the orifice size. For example, for a given flow velocity, a narrower orifice can achieve a higher level / height. Therefore, the orifice size can be selected based on the application: the length, angle, and / or height of the flow indicator channel; the desired flow velocity range measurable from the level / height in the flow indicator channel; and / or the desired measurement resolution. For example, for a flow indicator channel with a given maximum height, the maximum measurable flow velocity (before liquid overflows its upper end) is greater with a wider orifice than with a narrower orifice. However, a higher resolution scale (i.e., markings / gradations at smaller flow velocity intervals) can be used with a narrower orifice. Similarly, when the flow indicator channel is angled, a wider orifice can be used due to the expansion of the vertical component of the scale.

[0044] The shape of the flow resistance passage can be such that, when the insert is inserted into the drip chamber and arranged substantially vertically, the liquid remains in the flow resistance passage when the liquid flow stops. When the insert is arranged substantially vertically, the flow resistance liquid passage can be substantially U-shaped. In this document, "U-shaped" means that the direction of liquid flow is substantially reversed when passing through the flow resistance passage (including V-shapes, C-shapes, etc.). Therefore, the flow resistance passage includes a section in which the liquid flows substantially upward when the insert is arranged substantially vertically. The flow resistance passage may also include additional tortuous sections and / or curved sections.

[0045] The roughly U-shaped flow resistance path prevents the path from drying out and remains moist when the operator stops the liquid flow. This prevents the accumulation of solid deposits in the flow resistance path, which can occur due to liquid evaporation. Such accumulations can affect the cross-sectional area of ​​the flow resistance path, thereby affecting flow resistance and introducing errors into the liquid flow rate measurement from the flow indicator channel.

[0046] When the flow resistance path includes an orifice, and the insert is arranged substantially vertically, the orifice can be located at or near the lower part of the U-shaped flow resistance path. This ensures that the orifice is submerged during use (preventing it from drying out) and that droplets do not form in the restricted areas of liquid flow. Avoiding droplet formation improves the reliability of the resulting flow meter device, as droplet volume or formation rate may be inconsistent.

[0047] Inserts can be formed using molding processes, such as injection molding. Specifically, inserts can be single-piece molded parts. Optionally or preferably, inserts can be formed using a unidirectional injection molding process. A unidirectional molding process refers to a mold for manufacturing the insert consisting of two parts that separate in a single direction (i.e., no side cores or complex tools are required). This reduces manufacturing time and cost. Furthermore, because flow resistance passages can be formed between the insert and the wall (inner surface) of the drip chamber, the critical geometry and dimensions of the flow resistance passages (e.g., orifices) can be achieved using conventional injection molding techniques and tolerances. For example, when the insert is arranged substantially vertically, the inlet passage can be formed at an angle to the vertical direction (or at an angle to the longitudinal axis) such that the outlet end of the inlet passage extends to the outer surface of the insert and / or communicates with one or more grooves or open channels in the outer surface of the insert. Optionally, inserts can be formed using 3D printing or machining processes.

[0048] Devices relying on the same principle that the liquid level or height in the indicator column is proportional to the flow rate through the flow resistance passage have historically been unreliable at low flow rates (below 50 mL / h) and / or require high tolerances and expensive manufacturing costs. The insert of this invention improves the accuracy and consistency of flow indication even at low flow rates, can be manufactured within standard injection molding tolerances, and can be used with standard drip chambers widely available and used in the art.

[0049] The insert may also include an outlet chamber for guiding liquid flow from the flow-resistance passage to the outlet. The outlet chamber may communicate with the outlet end and outlet of the flow-resistance passage. The outlet chamber may include an outlet. The outlet chamber may include an opening in its sidewall that communicates with the outlet end of the flow-resistance passage. When the insert is arranged vertically, the sidewall opening and / or outlet end of the flow-resistance passage may be located at a horizontal position or height above the outlet level / height. The outlet chamber may include a base plate, bottom, or bottom wall, with the outlet located within the base plate, bottom, or bottom wall.

[0050] The outlet chamber may include a channel extending from a sidewall opening of the flow-resistance passage and / or an outlet end to guide liquid from the flow-resistance passage and / or direct it to the outlet without forming droplets. This channel may be a secondary channel. The channel may be configured to draw liquid (e.g., substantially downwards) into the outlet chamber via capillary action. The channel may be or include at least a portion of an open channel or groove formed in the sidewall of the outlet chamber. The open channel may extend to the floor, bottom, or bottom wall of the outlet chamber.

[0051] The outlet chamber may be at least partially defined by an insert. The outlet chamber may be partially defined by the insert such that, when the insert is inserted into the drip chamber, the outlet chamber is formed between the insert and the wall (e.g., sidewall or outer wall) of the drip chamber. The outlet chamber may be formed by a groove in the insert. During assembly, at least a portion of the groove may be closed by the wall (e.g., sidewall or outer wall) of the drip chamber. The wall of the drip chamber may form at least a portion of the sidewall of the outlet chamber.

[0052] The outlet chamber may also include an overflow opening located at a level or height between the outlet level / height and the sidewall opening of the flow resistance passage and / or the outlet end level / height. When inserted into the drip chamber, the overflow opening may communicate with the lower part of the drip chamber below the insert, allowing liquid overflowing from the outlet chamber to drain into the lower part of the drip chamber. This prevents liquid from accumulating in the outlet chamber, which would otherwise introduce errors in flow rate measurements (particularly the "zero line") from the flow indicator channel. The overflow opening also allows air to flow between the outlet chamber and the lower part of the drip chamber. Furthermore, the outlet chamber may include one or more vent openings located above the overflow outlet level / height, communicating with the interior of the drip chamber to allow air to flow between the outlet chamber and the rest of the drip chamber. Thus, the outlet chamber can be an open chamber.

[0053] The insert can also be shaped and constructed to provide a gap between the insert and the wall of the drip chamber. This gap can extend along the length of the insert. The gap can be located on a chamfered side of the insert, or in a channel or recess. Overflow openings, gaps, and / or venting openings prevent airlocks from forming in any / all non-liquid-filled passages / channels / chambers and allow the resulting flowmeter device to be “pre-charged” in the same manner as existing dripping devices, which involves squeezing and releasing the flexible portion (lower part) of the drip chamber to draw liquid downwards from the liquid source through the main liquid flow channel and expel air upwards into the liquid source.

[0054] The insert may also include one or more side ribs, panels, and / or protrusions extending from the insert toward the outer wall of the drip chamber. One or more side ribs and / or protrusions may facilitate a tight interference fit within the drip chamber and increase the structural strength / stiffness of the insert, for example, resisting bending, deflection, and / or torsion of the insert. One or more side ribs and / or protrusions may extend in a substantially longitudinal and / or transverse direction. Side ribs or protrusions may include one or more openings or notches configured to prevent trapping of air or liquid.

[0055] The insert may also include a filter element located upstream of the flow resistance passage to prevent particles in the liquid from depositing in the flow resistance passage, which would otherwise adversely affect the reliability of the resulting flow meter device. The filter element may be located at or near the inlet end of the inlet passage. The filter element may be molded into / within the inlet passage.

[0056] The indicating chamber may include a restricted inlet with a size less than 1 mm, less than 0.75 mm, less than 0.5 mm, or less than 0.25 mm. The indicating chamber may additionally have a cross-sectional diameter of substantially 2.5 mm (or in the range of 2.0 mm to 3.0 mm) and a length of substantially 46 mm (or in the range of 41 mm to 51 mm).

[0057] In use, the restricted inlet of the indicator chamber may be located at: (i) the lower end of the orifice of the flow resistance passage; and / or (ii) the lower end of the exhaust passage.

[0058] According to a second aspect of the invention, a flow meter device is provided, comprising an insert as described in the first aspect and a flow chamber or housing for receiving the insert.

[0059] The flow chamber or housing may include an opening through which an insert can be inserted, and an outlet for receiving liquid flow from the insert outlet. The outlet of the flow chamber may be located downstream of the insert outlet for connection to other downstream components of the device, such as piping, fittings, and / or flow controllers. The flow chamber may include one or more walls (e.g., sidewalls or an outer wall). Features of the insert defined by the walls of the drip chamber in the first aspect can also be defined by reference to the walls of the flow chamber. The walls may define an internal volume, cavity, or space sized to accommodate the insert. The walls may extend from the opening in the insertion direction. At least one of the one or more walls may include a substantially transparent portion for observing the liquid level / height in the flow indication channel.

[0060] The internal volume, cavity, or space of the flow observation chamber can have a substantially circular cross-section (e.g., the interior of the flow chamber can be substantially cylindrical) or have a non-circular and / or arbitrary cross-section. The flow chamber or housing can be or includes a tube or tubular member. The flow chamber can be or includes a container or bag with openings, portions, and / or tubular sections configured to receive and / or accommodate an insert, such that the insert can provide a visual indication of the flow rate entering and / or passing through the container / bag / chamber. The inner surface of the wall can be tapered (inward) or non-tapered in the insertion direction. The wall of the drip chamber can be substantially rigid or flexible / deformable, or include substantially rigid portions and substantially flexible / deformable portions. The flow chamber or housing can be substantially tubular. The exterior of the flow chamber or housing can have a regular or irregular shape.

[0061] The flow chamber may be or include a drip chamber, such as a standard (at least partially) transparent drip chamber known in the art for IV dosing / drip devices. However, it should be understood that any flow chamber of suitable size may be used, particularly for non-IV applications.

[0062] The length of the flow chamber can be greater than the length of the insert. In the case that the flow chamber is a drip chamber for IV administration, it can have a length at least 40 mm longer than the length of the insert, and the outlet of the insert can be located at a position at least 5 mm away from the wall (inner surface) of the drip chamber to comply with ISO-8536-4.

[0063] The drip chamber can be approximately 100 mm long. The insert can be approximately 60 mm long. This leaves approximately 40 mm of usable reading scale for the flow indication channel.

[0064] The flow chamber can be a single component or comprise two or more independent parts that can be attached to each other. An opening for receiving an insert can be formed at the upper end of the flow chamber. The device may also include a cap or lid connectable to the flow chamber, having means for connecting the device to a liquid source (e.g., an intravenous bag or container). The cap or lid can connect to the opening of the flow chamber. The cap or lid can close and seal the flow chamber and define an inlet passage for liquid flow from the liquid source to the insert inlet passage. The cap or lid may include an inlet passage having an outlet end for connection to the insert inlet passage and an inlet end for connection to the liquid source.

[0065] Optionally, the cap or lid may be integral with the flow chamber. The flow chamber may include an inlet passage having an outlet end for connection to an insert and an inlet end for connection to a liquid source. In this case, the opening for receiving the insert may be the lower end of the flow chamber. The flow chamber may include separable upper and lower portions that can be attached to each other. The upper portion may include an inlet passage. The lower portion may include an outlet. The opening for receiving the insert may be formed at the lower end of the upper portion.

[0066] The outlet end of the inlet passage of the cap or lid or flow chamber can be connected to and / or sealed to the inlet passage (upper / inlet end) of the insert, for example, to prevent leakage and / or air ingress into the inlet passage. The outlet end of the inlet passage of the cap or lid or flow chamber can be configured to seal the inlet passage of the insert, and vice versa. For example, the outlet end of the inlet passage of the cap or lid or flow chamber can be configured to provide an interference fit with the inlet end, around the inlet end, or within the inlet end of the inlet passage of the insert, and vice versa. Optionally, the outlet end of the inlet passage of the cap / lid or flow chamber can be connected to the inlet passage of the insert via a sealing element. The device may include a sealing element that seals the outlet end of the inlet passage of the cap / lid or flow chamber to the inlet passage of the insert when the cap / lid is connected to the drip chamber or when the insert is inserted into the flow chamber. The sealing element may be or include a sealing ring that can be installed between the insert and the cap / lid or flow chamber. The cap / lid of the flow chamber may include a sealing element. For intravenous administration, the cap / lid may be or include a standard ventilated or non-ventilated puncture / perforation device for insertion or puncture of the fluid container, as known in the art. The inlet passage of the cap / lid may extend through the puncture / perforation device. Alternatively, where the drip chamber does not include a cap / lid, the drip chamber may include a puncture or perforation device.

[0067] The cap or lid can be configured to close and seal the opening of the flow chamber via an interference fit. Optionally or additionally, a sealing element, such as a sealing ring, can be used that can be fitted between the drip chamber and the cap / lid. The sealing element for sealing the inlet passage of the cap / lid to the inlet passage of the insert and the sealing element for sealing the cap / lid to the drip chamber can be an integral sealing element or a separate sealing element.

[0068] The device may also include one or more filter elements for filtering liquid upstream of the insert. The filter element may be configured to be fitted between the insert and the cap / lid, and at least cover the inlet end of the inlet passage of the insert. The filter element may also be configured to provide a seal between the inlet passage of the insert and the inlet passage of the cap / lid. A sealing element may include the filter element, or vice versa. Where the insert includes a filter element, a separate filter element may not be necessary. The cap / lid may be separate from the insert. Optionally, the insert may include a cap / lid.

[0069] According to a third aspect of the invention, an IV administration kit is provided, comprising one or more inserts according to a first aspect. The kit may include one or more flow meter devices according to a second aspect. The kit may also include one or more at least partially transparent drip chambers for receiving the inserts. The drip chambers may be standard drip chambers for IV administration, as known in the art. The drip chambers may include an outlet for receiving a flow of fluid from an insert outlet, for example, located downstream of the insert outlet. The kit may also include one or more caps or lids for the drip chambers. The caps or lids may include means for connecting an inlet passage of the insert to a fluid source. The caps or lids may include an inlet passage having an outlet end for connection to the inlet passage of the insert and an inlet end for connection to the fluid source. As known in the art, the caps or lids may be or include a standard ventilated or non-ventilated puncture device for puncturing a fluid source (e.g., an intravenous bag or rigid container).

[0070] Optionally, the drip chamber may include a cap / lid. The drip chamber may include an inlet passage having an outlet end for connection to an insert and an inlet end for connection to a liquid source. The drip chamber may also include means for connecting the insert's inlet passage to a liquid source, such as a puncture needle or puncture device. The drip chamber may be a single-piece drip chamber or a multi-piece drip chamber, for example, including an upper and lower section that can be interconnected.

[0071] The kit may also include tubing for connecting the outlet of the drip chamber to the point of administration. The kit may also include one or more flow control devices. The flow control device may be or include a clamping device for clamping the tubing, such as a roller clamp valve or clamp valve known in the art. Alternatively, the flow control device may be used for connection in series with the tubing. The IV administration kit may be used with or include other standard accessories known in the art, including but not limited to three-way stopcocks, injection ports, cannulas, Luer locks, and / or shut-off clamps.

[0072] The outlet end of the inlet passage of the cap / lid can be connected to the inlet passage of the insert via an interference fit. Alternatively, the outlet end of the inlet passage of the cap / lid can be connected to the inlet passage of the insert via a sealing element.

[0073] The kit may also include one or more filter elements for filtering the liquid flow upstream of the insert. The filter element may be configured to fit between the insert and the cap / lid, and at least cover the inlet end of the insert's inlet passage. Optionally or preferably, the sealing element may include the filter element.

[0074] According to a fourth aspect of the invention, a method of using an insert according to the first aspect, a method of using a flow meter device according to the second aspect, and / or a method of using an IV delivery kit according to the third aspect is provided.

[0075] The method may include inserting an insert into an opening of a drip chamber or flow chamber. The method may also include attaching a cap or lid to the opening of the drip chamber or flow chamber to close and / or seal the drip / flow chamber. Attaching the cap / lid may further include positioning a filter element between the inlet end of the insert's inlet passage and the outlet end of the cap / lid's inlet passage. Attaching the cap / lid may further include connecting and / or sealing the inlet end of the insert's inlet passage to the outlet end of the cap / lid's inlet passage. The method may further include connecting the inlet end of the cap / lid's inlet passage to a liquid source. Connecting to the liquid source may include puncturing the liquid container with a puncture needle or puncture device of the cap / lid. The method may also include connecting a tubing to the outlet of the drip / flow chamber to direct the liquid flow to the point of use / administration. The method may also include allowing the liquid to flow through a flow meter device. The method may also include reading the flow rate from a flow indication channel.

[0076] The step of inserting an insert into a dripping chamber or a flow chamber may include inserting the insert to form a flow resistance passage and / or a flow indication passage between the insert and the wall of the dripping chamber or flow chamber. The insertion step may include inserting the insert to close and / or seal one or more recesses or open channels in the mating surface of the insert, such that the recesses or open channels abut against the wall of the dripping chamber or flow chamber.

[0077] Features described in the context of independent aspects and / or embodiments of the invention may be used together and / or interchanged. Similarly, features described in the context of a single embodiment for the sake of brevity may also be provided individually or in any suitable sub-combination. Features described in connection with the apparatus may have corresponding features that are method-definable, and these embodiments are specifically contemplated. Attached Figure Description

[0078] To better understand the present invention, embodiments will now be discussed by way of example only with reference to the accompanying drawings, in which: Figure 1a and Figure 1b An exploded side view and a perspective view of the flow meter device according to the present invention are shown respectively; Figure 2 A side view of the assembled flow meter assembly shown in Figure 1 is illustrated, in which the insert is visible; Figure 3a and Figure 3b The other side view (where the insert is visible) and cross-sectional view of the assembled flow meter device in Figure 1 are shown respectively; Figure 4a Detailed perspective views of the insert shown in Figures 1 to 3 are displayed; Figure 4b It shows Figure 4a The outline of one or more recesses or open channels in the insert; Figure 4c and Figure 4d They are shown respectively Figure 4a Schematic horizontal and vertical cross-sections of the orifice of the flow resistance passage; Figure 4e Figure 4f shows a schematic vertical cross-section of the alternative orifice geometry; Figure 5a and Figure 5b The perspective views of the insert shown in Figures 1 to 4 from different angles are shown, indicating the liquid flow path; Figure 6 Enlarged views of the inserts shown in Figures 1 to 5 are displayed, indicating the liquid flow path; Figure 7 Figures 1 to 10 are shown from different angles. Figure 6 Another perspective view of the insert shows the oral cavity; Figure 8 A side view of the insert according to another embodiment of the present invention is shown; Figure 9 It shows Figure 8 A side view of the insert, with the direction of liquid flow indicated by arrows; Figure 11 It shows Figure 8 A magnified view of the insert; Figure 12 It shows Figure 8 A magnified view of the insert; Figure 13 It shows Figure 8 A magnified view of the insert; and Figure 14 It shows Figure 8 The rear view of the insert.

[0079] It should be noted that the accompanying drawings are schematic and may not be drawn to scale. For clarity and convenience in the drawings, the relative dimensions and scales of the parts may have been enlarged or reduced. In modified and / or different embodiments, the same reference numerals are generally used to refer to corresponding or similar features. Detailed Implementation

[0080] Figures 1a to 3bA flow meter device 100 according to aspects and / or embodiments of the present invention is illustrated. The device 100 includes a flow metering insert 10, a flow chamber or housing 50 for receiving the insert 10, and a cap or cover 30 for closing / sealing the flow chamber 50 and connecting the device 100 to a liquid source (not shown). The device 100 is assembled by inserting the insert 10 into the flow chamber 50 and attaching the cap or cover 30 to the flow chamber 50 to close and / or seal the flow chamber 50. The device 100 is configured to be arranged substantially vertically in use, such that liquid can flow downward through the device 100 under gravity. The terms "upper" and "lower" as used below refer to this direction, but it should be understood that aspects and embodiments of the invention are not limited to a particular direction.

[0081] In the illustrated embodiment, the flow chamber 50 is a generally tubular component including an opening, recess, or orifice 51 at an upper end to receive the insert 10, and an outlet 52 at a lower end for connection to other components downstream of the device 100, such as tubing and / or flow control devices (not shown). The opening, recess, or orifice 51 defines the internal volume or space of the chamber defined by the sidewalls 50w. It should be understood that the flow chamber 50 is not limited to the geometry shown; for example, the exterior of the walls 50w may have a regular or irregular shape, and the internal volume of the drip chamber 50 may be substantially cylindrical or non-cylindrical as shown, provided that at least a portion can receive and mate with the insert 10, as described below. The cap or lid 30 includes an inlet passage 32 for receiving a flow of liquid from a liquid source. In the illustrated example, the inlet passage 32 is formed in a protrusion or puncture device 31 for connecting the device 100 to a liquid source, for example, by inserting the puncture device 31 into the outlet of the liquid source or puncturing the liquid source. However, it should be understood that other means for fluidly connecting device 100 to a liquid source may be used, such as push-fit, threaded fit, or Lurul lock fittings known in the art. When connected to a liquid source, liquid enters device 100 through inlet passage 32 of cap / cover 30, flows through insert 10, enters flow chamber 50, and exits device 100 through outlet 52. Insert 10 provides a direct visual indication of the liquid flow rate through device 100, as explained further below. Therefore, at least a portion of flow chamber 50 must be formed of or comprise a substantially or at least partially transparent material such that at least a portion of insert 10 is visible through sidewall 50w of flow chamber 50.

[0082] In the illustrated embodiment, the flow chamber 50 is a standard drip chamber, and the cap / lid 30 is a standard ventilated or non-ventilated puncture / puncture device used in intravenous (IV) administration kits, as known in the art. The drip chamber 50 is constructed of a substantially transparent plastic material, wherein at least a portion of the sidewall 50w (i.e., the lower portion below the insert) is substantially flexible / deformable, allowing observation of fluid flow within the drip chamber 50, and pre-filling the IV kit in a conventional manner by squeezing and releasing the flexible / deformable portion of the drip chamber to draw fluid from the fluid source and expel air upwards into the fluid source (e.g., an intravenous bag or container). The outlet end 32b of the cap / lid's inlet passage 32 is configured to conform to ISO 8536-4 (i.e., located 5 mm from the inner surface of the sidewall 50w) and typically includes a drip-forming orifice, as conventionally used to form a drip to indicate the flow rate observed in the drip chamber 50. For example, depending on the desired droplet size / volume, the droplet forming orifice can be approximately 3 mm wide, or narrower or wider. However, it should be understood that the invention is not limited to IV administration, and therefore any suitable flow chamber 50 sized to accommodate the insert 10 (with substantially transparent sidewalls 50w) and any suitable cap / lid 30 having a means of connecting the device 100 to a liquid source can generally be used, particularly in non-IV applications.

[0083] Figure 4a , Figure 5a and Figure 5b Insert 10 is shown in more detail. Insert 10 includes an inlet passage 11, an outlet 13, and a flow resistance passage 12 between the inlet passage and the outlet 13. This defines a main liquid flow path through insert 10. Insert 10 also includes a flow indication passage 14, the lower end / inlet 14a of which is connected between inlet passage 11 and flow resistance passage 12. Figure 3b As shown, attaching the cap / lid 30 to the drip chamber 50 connects the inlet passage 32 to the inlet end 11a (upper end) of the inlet passage 11, thereby providing a liquid flow path from the liquid source to the inlet passage 11 of the insert 10. An interference fit or a separate sealing element can be used to provide a liquid-tight seal between the inlet passage 32 of the cap / lid 30 and the inlet passage 11 of the insert 10, which will be discussed further below.

[0084] The length of the insert 10 along its longitudinal axis is less than the length of the drip chamber 50. For IV administration, the length of the drip chamber 50 may be at least 40 mm longer than the length of the insert 10, and the outlet 13 of the insert 10 may be located at least 5 mm from the sidewall 50w (inner surface) of the drip chamber 50, in accordance with ISO-8536-4. However, it should be understood that for non-IV applications that do not require compliance with ISO-8536-4, the insert 10 only needs to be equal to or shorter than the length of the drip chamber 50 for installation therein. In one example, the length of the drip chamber 50 may be approximately 100 mm, and the length of the insert 10 may be approximately 60 mm, in accordance with ISO-8536-4. Furthermore, the outlet 13 of the insert 10 may be or include a drip forming orifice (e.g., an orifice approximately 3 mm wide), such that, according to ISO-8536-4 (which requires continuous drip visibility in medical gravity infusion devices), a drip flow can still be seen in the drip chamber 50 when the liquid leaves the insert 10. In an insert approximately 60 mm long, the inlet passage 11 may be approximately 40 mm long, which can promote laminar flow.

[0085] In a standard trocar 30 used for IV injection, the outlet end 32b is typically chamfered. The shape of the inlet end 11a of the inlet passage 11 can accommodate this and provide an interference fit with the outlet end 32 to connect and seal the inlet passage 11 of the insert to the inlet passage 32 of the cap / lid 30. Alternatively, when the cap / lid 30 is attached, a separate sealing ring (not shown) can be provided to seal the interface (not shown) between the inlet passage 11 of the insert and the inlet passage 32 of the cap / lid 30.

[0086] The flow resistance passage 12 includes an inlet end 12a, an outlet end 12c, and a flow-limiting orifice 12b between the inlet end 12a and the outlet end 12c. The outlet end 11b (lower end) of the inlet passage 11 is connected to the inlet end 12a of the flow resistance passage 12. The lower end 11b of the inlet passage 11 is also connected to the flow indication channel 14. Specifically, as Figure 3a As shown, the flow indication channel 14 includes an inlet end (lower end) 14a communicating with the lower end 11b of the inlet passage 11 and the inlet end 12a of the flow resistance passage 12, and extends generally upward from its lower end 14a to an open outlet end 14b (upper end). The open upper end 14b of the flow resistance passage 14 communicates with the internal volume 51 of the drip chamber 50 (and the portion of the drip chamber 50 below the insert 10).

[0087] like Figure 4a , Figure 5a and Figure 5bAs shown, the flow resistance passage 12 and the flow indication channel 14 are partially defined by one or more grooves or open channels 10r in the surface 10m. For greater clarity, the contours of the one or more grooves or open channels 10r are defined by... Figure 4b The thick lines in the figure show the insert 10. The insert 10 is shaped and configured to have an interference fit within the drip chamber 50, such that when the insert 10 is inserted into the drip chamber 50, one or more recesses or open channels 10r are closed and sealed against the sidewall 50w of the drip chamber 50. The interference fit is provided by one or more mating surfaces 10m, 10m', which are configured to contact the inner surface of the sidewall 50w when the insert 10 is inserted into the drip chamber 50. One or more recesses or open channels 10r are formed in the mating surface 10m, which is configured to receive, conform to, and seal the inner surface of the sidewall 50w when the insert 10 is inserted into the drip chamber 50. Thus, when the insert 10 is inserted into the drip chamber 50, a flow resistance passage 12 and a flow indication passage 14 are formed between the insert 10 and the inner surface of the sidewall 50w. The mating surface 10m can be configured to at least partially deform the inner surface of the sidewall 50w, and / or be at least partially deformed by the inner surface of the sidewall 50w, to fit therebetween and form a liquid-tight seal. For example, if the insert 10 is formed of or includes a substantially rigid material, the sidewall 50w of the drip chamber 50 can be substantially flexible or less rigid than the insert, such that when the insert 10 is inserted into the drip chamber 50, the inner surface of the sidewall 50w is at least partially bent or deformed to fit against the mating surface 10m of the insert 10. Alternatively, if the insert 10 is formed of or includes a substantially deformable material, the sidewall 50w of the drip chamber 50 can be substantially rigid, such that the mating surface 10m is at least partially deformed to fit against the inner surface of the sidewall 50w. In either case, the mating surface 10m is configured such that when the insert 10 is inserted into the drip chamber 50, the mating surface 10m can conform to (after deformation or no deformation) the final inner surface of the sidewall 50w.

[0088] The mating surface 10m may extend at least partially around the side of the insert 10, and / or additional mating surfaces 10m' may be provided at different locations around the side of the insert 10 to facilitate a tight interference fit within the drip chamber 50. In the illustrated embodiment, as Figure 5a , Figure 5b and Figure 7As shown, an additional mating surface 10m' is provided on ribs or panels 16, 17 extending toward and / or between sidewalls 50w. The mating surfaces 10m, in which the flow resistance passage 12 and flow indication passage 14 are partially defined, are continuous and substantially smooth surfaces to provide uniform sealing contact with the sidewalls 50w and prevent leakage. Optionally or additionally, the mating surfaces 10m, 10m' may be or include one or more sealing ribs that reduce the contact area and facilitate a liquid-tight seal (not shown) against the inner surface of the sidewalls 50w of the drip chamber 50. For example, the mating surface 10m may include one or more sealing ribs extending around the periphery of one or more recesses or open channels (not shown). The sealing ribs may have a generally circular or triangular profile and may be configured to deform, or be deformed by, the inner surface of the sidewalls 50w to form a liquid-tight seal therebetween.

[0089] Insert 10 may be formed of or comprise a substantially rigid material, such as acrylonitrile-butadiene-styrene (ABS) or any other substantially rigid plastic permitted for use in IV applications. In this case, insert 10 may be provided with an interference fit within a substantially flexible / deformable portion of the drip chamber 50 to provide a liquid-tight seal therebetween. Alternatively, insert 10 may be formed of or comprise a substantially flexible, deformable, and / or compressible material, such as polyvinyl chloride (PVC) or any non-PVC equivalent plastic permitted for use in IV applications. In this case, insert 10 may be provided with an interference fit within a substantially rigid portion of the drip chamber 50 to provide a liquid-tight seal therebetween.

[0090] During use, the liquid flowing through the inlet passage 11 encounters the side wall 50w of the drip chamber 50 and is forced to flow into the flow resistance passage 12. The flow resistance provided by the orifice 12b causes the liquid to enter the adjacent flow indication channel 14, such as... Figure 5a and 5b As shown by the arrow in the image. Figure 6 The arrows further illustrate the liquid flow through insert 10. The liquid level or height in flow indication channel 14 will rise to a height proportional to the liquid flow rate through flow resistance passage 12 (explained further below), which can be adjusted by an external flow control device (not shown). Figure 8 As shown in Figure a, a scale 60 with calibration graduations 60i can be placed on, beside, or near the flow indication channel 14 to provide a clear reading of the liquid flow rate. A visible float can also be provided in the flow indication channel 14 to facilitate reading the liquid level / scale 60. The scale 60 may be included in the insert 10 or the drip chamber 50 if desired.

[0091] The operating principle of device 100 is as follows: Based on the width of orifice 12b and the liquid flow velocity, the flow resistance liquid passage 12 provides resistance to liquid flow and the associated pressure drop. As liquid flows through orifice 12b, its pressure increases slightly upstream of orifice 12b before decreasing downstream, and eventually rises again further downstream as the flow expands. The pressure P at the bottom of the liquid column in flow indication channel 14 is given by P = ρgh, where ρ is the liquid density, g is the gravitational constant, and h is the liquid height. Therefore, the flow resistance caused by orifice 12b causes upstream liquid to flow back into flow indication channel 14 and reach height h according to the pressure drop. The flow velocity through orifice 12b is essentially the same as the flow velocity in the rest of the main liquid flow passage 12. Therefore, the liquid flow rate through device 100 can be read directly from the liquid level / height in flow indication channel 14 via scale 60 (unless the flow velocity is high enough to overflow indication channel 14, as described below).

[0092] In this embodiment, orifice 12b has a width approximately between 0.1 mm and 0.2 mm. This provides suitable flow resistance, thus providing discernible level / height changes in the flow indication channel 14 for flow rates in the range of approximately 0-250 mL / h, covering a scale 60 of approximately 40 mm. However, it should be understood that other orifice widths may be used depending on the application of device 100 (e.g., the required scale size and / or the flow rate to be measured). Using a throttling orifice (rather than a long, narrow conduit / pipe section) makes the flow meter device 100 less sensitive to changes in liquid viscosity. Therefore, preferably, orifice 12b is as close to having no length (in the flow direction) as possible (within the constraints of the manufacturing process). Figure 4a and Figure 4b As shown, the orifice 12b is formed by a generally V-shaped protrusion 10p that extends from the wall of the groove 10r or the flow-resistance passage 12, narrowing the width of the passage. Figure 4c As shown, in the horizontal cross-section, the protrusion 10p extends from the bottom of the groove 10r and faces the wall 50w of the drip chamber 50. Furthermore, as... Figure 4d As shown, the protrusion 10p can extend in a vertical section from the sidewall of the groove 10r or the flow resistance passage 12 to the substantially straight portion of the opposite groove sidewall.

[0093] Figure 4e An embodiment is shown, wherein the orifice 12b is formed by two protrusions 10p-1 and 10p-2. Similar to... Figure 4d , Figure 4e The orifice 12b is shown in a vertical section. Protrusions 10p-1 and 10p-2 are asymmetrical (in...). Figure 4eIn these embodiments, they are triangular (but in other embodiments they may take any other shape), and define a first face 12b-1 and a second face 12b-2 of the orifice 12b. For clarity, in use, when liquid passes through the orifice 12b, the liquid flows from the first face 12b-1 to the second face 12b-2 (in... Figure 4e (From right to left).

[0094] When the insert 10 is in the upright position, the first surface 12b-1 is substantially vertical. The first surface 12b-1 is substantially perpendicular to the bottom surface of the groove 10r. The first surface 12b-1 is substantially parallel to the plane 12b-A defined by the orifice 12b. The second surface 12b-2 is at an angle relative to the plane 12b-A defined by the orifice 12b.

[0095] The angle of the second face 12b-2 relative to the orifice plane 12b-A is defined by the angle θ1 of the first protrusion 10p-1 and the angle θ2 of the second protrusion 10p-2. Figure 4e In the first projection 10p-1, the angle θ1 is equal to the angle θ2 of the second projection 10p-2. However, in other embodiments, the angles θ1 and θ2 may be different.

[0096] Having a first surface 12b-1 substantially parallel to the plane 12b-A of the orifice 12b and a second surface 12b-2 angled relative to the plane 12b-A of the orifice 12b reduces the influence of liquid viscosity, while simplifying manufacturing and allowing for larger manufacturing tolerances. In some embodiments of the invention, the second surface 12b-2 forms an angle between 20° and 55° relative to the plane 12b-A of the orifice 12b. In some embodiments of the invention, the second surface 12b-2 forms an angle between 25° and 50° relative to the plane 12b-A of the orifice 12b. In some embodiments of the invention, the second surface 12b-2 forms an angle between 30° and 45° relative to the plane 12b-A of the orifice 12b.

[0097] The flow-resistance liquid passage 12 is substantially U-shaped (when the insert 10 and device 100 are arranged substantially perpendicularly), such that the direction of liquid flow is substantially reversed as it passes through the flow-resistance liquid passage 12. The orifice 12b is positioned towards the bottom of the U-shaped flow-resistance liquid passage 12. The U-shaped flow-resistance liquid passage 12 is configured such that liquid remains in the flow-resistance liquid passage 12 when the operator stops the flow. This prevents the orifice 12 from drying out, which would lead to the accumulation of solid deposits or crystals, altering the size of the orifice 12b and adversely affecting its function. For example, a reduction in the width of the orifice 12b would introduce errors in the liquid flow reading in the flow indication channel 14, and eventually, blockage of the orifice 12b would completely stop the flow of liquid in the insert 10.

[0098] like Figure 7As shown, after passing through orifice 12b, the liquid flows substantially upward to the outlet end 12c of the flow-resistance passage 12 and enters the outlet chamber 15 through opening 15a. This flow, by submerging orifice 12b, prevents droplet formation in the restricted flow portion. The purpose of the outlet chamber 15 is to guide the liquid flow towards the outlet 13, which is formed at the bottom of the outlet chamber 15. When the insert 10 is arranged substantially vertically, opening 15a is located above the level / height of outlet 13, allowing the liquid to drain downwards into outlet 13. The outlet chamber 15 includes a narrow channel 15b extending from opening 15a to the bottom of the outlet chamber 15. The narrow channel 15a draws the liquid downwards into the outlet chamber via capillary action. Therefore, as the liquid flows from opening 15a to outlet 13, the formation of irregular droplets, which would render flow rate measurements unreliable, is prevented. The narrow channel 15b can be a closed channel or an open channel. In the illustrated embodiment, the narrow channel 15b is an open channel. The narrow open channel 15b can be formed by a groove in the sidewall of the outlet chamber 15, and therefore can be easily formed by conventional molding processes. The cross-section of the narrow open channel 15b is ideally semi-circular, with a width of less than 1 mm (approximately 0.5 mm).

[0099] The outlet chamber 15 includes an overflow opening 15c communicating with the internal volume 51 of the drip chamber 50 (particularly the portion of the drip chamber 50 below the insert 10). The overflow outlet 15c is located between the outlet 13 and the opening 15a at a horizontal / height level to prevent liquid from filling the outlet chamber 15, which would otherwise introduce errors to the flow rate measurement (particularly the "zero line") of the flow indication channel 14. In the illustrated embodiment, the overflow opening 15c is formed by a recess in the panel 16, and the outlet chamber 15 opens to the internal volume 51 of the drip chamber 50, so that it does not enclose the space. The open outlet chamber 15 and / or overflow opening 15c allow air to flow between the outlet chamber 15 and the lower portion of the drip chamber 50. This prevents airlock and allows the device 100 to be "pre-charged" in the same manner as existing drip kits, which involves squeezing and releasing the lower portion of the drip chamber 50 to draw liquid downwards from the liquid source through the main liquid passage and expel air upwards into the liquid source.

[0100] The insert 10 can also be shaped and configured to provide a gap G between the insert 10 and the sidewall 50w of the drip chamber 50, the gap extending along the length of the insert 10. The gap G can further facilitate airflow (and "pre-filling" as described above) between the outlet chamber 15 and the internal space 51 of the drip chamber 50. Figure 7 As shown, in the illustrated embodiment, the gap G is provided by a panel 16 that forms the chamfered side 16 of the insert 10. Figure 7 The dashed line in the figure represents the position of the side wall 50w when the insert 10 is inserted into the drip chamber 50, and the gap G formed between the side wall 50w and the panel 16.

[0101] The inlet passage 11 may include a filter element (not shown) to filter the liquid before it reaches the flow resistance passage 12 and prevent any blockage caused by particles contained in the liquid. The filter element may be located at or near the upper end 11a of the inlet passage 11. The filter element may be integrated with the insert 10. Optionally or additionally, the device 100 may include a separate filter element that may be installed between the insert 10 and the cap / lid 30 and / or between the drip chamber 50 and the cap / lid 30. Such a filter element may be integrated with a sealing ring (if present) to seal the interface between the inlet passage 32 of the cap / lid 30 and the inlet passage 11 of the insert 10 and / or to seal the interface between the cap / lid 30 and the upper end of the drip chamber 50. For example, the device 100 may include a flexible insert ring that contains the filter element (not shown).

[0102] Figure 8 An embodiment of insert 10 is shown, which also includes an exhaust channel 18. Insert 18 also includes a second orifice 12d, which will be described below. Figure 11 and Figure 12 To provide a more detailed description.

[0103] As shown in the figure, the vent passage 18 is a substantially vertical column extending parallel to the flow indicator passage 14, with its lower end 18a in fluid communication with the lower end / outlet end 11b of the inlet passage 11 and having an open upper end 18b. The vent passage 18 is configured to allow any air bubbles in the liquid flowing out of the inlet passage 11 to rise upwards in the vent passage 18, rather than entering the flow indicator passage 14, which would otherwise adversely affect flow rate measurement / readings. It should be understood that the liquid, along with any air bubbles, can flow upwards along the vent passage 18. If there are no air bubbles in the liquid flow leaving the inlet passage 11, the liquid will rise and fall to the same level in both the flow indicator passage 14 and the vent passage 18. The vent passage 18 ensures that the liquid level in the flow indicator passage 14 is substantially free of air bubbles and provides accurate flow rate readings.

[0104] In use, the liquid (and any trapped air bubbles) travels from the lower end / outlet end 11b of the inlet passage 11 and enters the exhaust passage 18 via the lower end (inlet) 18a. This flow of liquid (and trapped air) is achieved through... Figure 9 The arrows indicate this. During use, when the rate at which liquid enters the insert 10 slows down or temporarily stops, the liquid remains within the insert 10. The liquid remains... Figure 9The liquid level indicated by line 19 (referred to as the "minimum liquid level") is shown. The lower end 18a of the vent passage 18 is positioned below the minimum liquid level 19 to ensure that the lower end 18a of the vent passage 18 is always submerged during use. Positioning the lower end 18a of the vent passage 18 below the minimum liquid level 19 ensures that air bubbles are not introduced into the flow indication chamber 11 through the vent passage 18.

[0105] The exhaust passage 18 includes an orifice 18c. The orifice 18c provides an additional flow path for the liquid in the exhaust passage 18 to flow towards the outlet 13 (e.g., Figure 14 (As shown). Because liquid can flow out of the venting channel 18 through orifice 18c, the flow rate must be high enough to overcome the loss rate of liquid through orifice 18c so that the liquid level is above the height of orifice 18c. Therefore, the ratio between flow rate and liquid level changes for liquid levels above and below orifice 18c.

[0106] Figure 10a and Figure 10b Exemplary scales 60 and 62 are shown respectively, which can be used to indicate flow rate based on the liquid level / height in the flow indication channel 14. A visible float (not shown) can also be provided in the flow indication channel 14 to improve the readability of the scales.

[0107] In the embodiment shown in Figures 1-7, the flow indication channel 14 has a substantially constant horizontal cross-section, is substantially straight, and extends substantially vertically from its lower end 14a when the insert 10 is arranged substantially vertically. In this case, as Figure 10a As shown, a linear scale 60 with regularly spaced graduations 60i can be used to indicate flow rate based on liquid level / height. However, it is understood that the flow indication channel 14 is not necessarily straight, vertical, and / or has a constant horizontal cross-section that varies with liquid level / height.

[0108] exist Figure 8 In the embodiment shown, an exhaust passage 18 with an orifice 18c is included, and a flow indication passage 14 extends substantially vertically from its lower end 14a. A scale 62 can be used instead. Figure 10aThe scale 60. The scale 62 includes regularly spaced graduations 62i, which can be used to indicate flow rate. The scale 62 is divided into a first section 62-1 and a second section 62-2. In the first section 62-1, graduations 62i represent flow rate increments of 25 ml / h. In the second section 62-2, graduations 62i represent flow rates of 50 ml / h. The flow rate increments of each graduation 62i are increased in the second section 62-2 to account for liquid loss through the vent orifice 18c. The level of liquid in the vent passage 18 reaching the orifice 18c corresponds to the level in the indicating chamber 14, at which point the scale 62 transitions from the first section 62-1 to the second section 62-2. The second section 62-2, with its increasing flow rate increments between graduations 62i, allows for monitoring of larger liquid flow rates, such as when administering a liquid bolus.

[0109] The flow rate values ​​shown on scales 60 and 62 are for illustrative purposes only, and those skilled in the art will recognize that other flow rate values ​​and increments may be used.

[0110] Figure 11 and Figure 12 An enlarged perspective view of the insert 10 is shown, revealing a second orifice 12d arranged in series with the first orifice 12b of the flow resistance passage 12. In use, liquid flows through the first orifice 12b into the recess 12e. The liquid then flows from the recess 12e through the orifice 12d to the outlet end 12c of the flow resistance passage 12. The second orifice 12d, arranged in series with the first orifice, enables a higher level of fluid resistance without requiring high-precision molding to form a narrower orifice.

[0111] The second orifice 12d can be identical to the first orifice 12b. The second orifice 12d can have any form as described with respect to the first orifice 12b, for example... Figure 14 c to Figure 14 The form shown in e. In one embodiment, the first orifice 12b and the second orifice 12d include a first surface substantially parallel to the orifice plane and a second surface angled relative to the orifice plane to reduce the influence of liquid viscosity, while simplifying manufacturing and allowing for greater manufacturing tolerances. In some embodiments of the invention, the second surface of each orifice forms an angle between 30° and 45° relative to the orifice plane.

[0112] Figure 12 The limiting part 14c at the inlet 14a of the flow indication channel 14 is also shown. Figure 13 The diagram also shows a limiting part 14c. The limiting part 14c reduces the size of the inlet 14a of the flow indicator channel 14, thereby reducing the possibility of air bubbles entering the flow indicator channel 14.

[0113] The size of inlet 14a can be reduced by the limiting part 14c, such that the maximum size of inlet 14a is equal to or less than the maximum size of the first orifice 12b. In some embodiments, the maximum size of the first orifice is 0.5 mm. The size of inlet 14a can be reduced by the limiting part 14c, such that the maximum size of inlet 14a is less than or equal to 1 mm. The size of inlet 14a can be reduced by the limiting part 14c, such that the maximum size of inlet 14a is less than or equal to 0.75 mm. The size of inlet 14a can be reduced by the limiting part 14c, such that the maximum size of inlet 14a is less than or equal to 0.5 mm. The size of inlet 14a can be reduced by the limiting part 14c, such that the maximum size of inlet 14a is less than or equal to 0.25 mm.

[0114] Inlet 14a is positioned such that, in use, inlet 14a is lower than the first orifice 12b. Inlet 14a is positioned such that, in use, inlet 14a is lower than the lower end (inlet) 18a of exhaust passage 18. Inlet 14a is positioned below the first orifice 12b, and the inlet 18a of exhaust passage 18 reduces the possibility of air bubbles entering the indicator chamber 14 or exhaust passage 18.

[0115] Figure 14 A perspective rear view of the insert 10 is shown. The vent 18c is visible, and from... Figure 14 It can be clearly seen that fluid can flow from orifice 18c to outlet 13.

[0116] Insert 10 includes multiple ribs 20. Figure 14 In one embodiment, there are three ribs, but in other embodiments, there may be any number of ribs, such as five ribs, or alternatively, two, four, six, seven or more. Ribs 20 are configured to trap fluid between them and retain the fluid near the rear of the outlet end 12c of the flow-resisting passage 12. In such an embodiment, fluid flowing out of the flow-resisting passage 12 contacts the fluid trapped between the ribs and is drawn downwards toward the outlet 13 to prevent accumulation.

[0117] Other variations and modifications will be apparent to those skilled in the art upon reading this disclosure. Such variations and modifications may involve equivalent and other features known in the art and may be used to replace or supplement the features already described herein.

[0118] Although the appended claims address specific combinations of features, it should be understood that the scope of the invention also includes any novel feature or any novel combination of features or any generalization thereof explicitly or implicitly disclosed herein, whether or not it relates to the same invention currently claimed in any of the claims, and whether or not it alleviates any or all of the same technical problems as the present invention.

[0119] Features described in the context of a single embodiment may also be provided in combination in a single embodiment. Conversely, for the sake of brevity, the various features described in the context of a single embodiment may also be provided individually or in any suitable sub-combination.

[0120] For completeness, it is also stated that the term "comprising" does not exclude other elements or steps, the term "a" or "an" does not exclude multiple, and any reference numerals in the claims should not be construed as limiting the scope of the claims.

Claims

1. A flow metering insert for a drip chamber, suitable for intravenous drug administration, said insert comprising: The main liquid flow channel includes: entrance access; Exports; and A flow resistance passage located between the inlet passage and the outlet passage, the flow resistance passage including an orifice; and A flow indicator channel, which communicates with the main liquid flow channel between the inlet passage and the flow resistance passage; The flow resistance passage and flow indication channel are at least partially defined by one or more first grooves and / or channels in the insert, and the flow resistance passage and flow indication channel are formed or located between the insert and the wall of the drop chamber when the insert is inserted into the drop chamber. The orifice of the flow resistance passage provides resistance to the liquid flow through the main liquid flow channel, forcing the liquid to enter the flow indicator channel and reach a level or height in the flow indicator channel that is proportional to the liquid flow velocity through the main liquid flow channel. The orifice is defined by a first surface and a second surface, the first surface being parallel to the plane defined by the orifice, and the second surface forming an angle between 20° and 55° with respect to the plane of the orifice.

2. The flow metering insert according to claim 1, wherein, The orifice is a first orifice, and the flow resistance passage includes a second orifice arranged in series with the first orifice.

3. The flow metering insert according to claim 2, wherein, The second opening is defined by a first surface and a second surface, the first surface being parallel to the plane defined by the opening, and the second surface forming an angle between 20° and 55° with respect to the plane of the opening.

4. The flow metering insert according to any one of the preceding claims, wherein, When the insert is arranged substantially vertically, the flow resistance path is substantially U-shaped, such that when the insert is inserted into the dripping chamber and is set substantially vertically, the liquid remains in the flow resistance path when the liquid flow stops.

5. The flow metering insert according to claim 4, wherein, The flow metering insert also includes an exhaust channel configured to release air bubbles from the insert, wherein the exhaust channel includes a lower end connected to the inlet passage and located upstream of the flow resistance passage, such that in use, the lower end of the exhaust channel is below a minimum liquid level defined by the liquid retained in the main liquid flow passage.

6. The flow metering insert according to claim 5, wherein, The venting passage is configured such that, during use, liquid is forced into the venting passage and the indicating chamber, such that the liquid in the venting passage reaches a level or height within the venting passage; and The relationship between the liquid level or height in the indicator chamber and the liquid level or height in the exhaust channel is linear.

7. The flow metering insert according to claim 6, wherein, The exhaust passage includes an orifice configured to allow liquid to flow out of the exhaust passage and into the outlet when the liquid level or height in the exhaust passage reaches the orifice.

8. The flow metering insert according to claim 7, wherein, When the liquid level or height in the exhaust channel reaches or exceeds the orifice, the ratio between the liquid level or height in the flow indicator channel and the liquid flow velocity through the main liquid flow channel decreases.

9. The flow metering insert according to any one of the preceding claims, wherein, The flow indication channel includes a scale to provide a visual measurement of the liquid level or height in the flow indication channel, thereby providing a measurement of the liquid flow rate through the main liquid flow channel; and optionally or preferably, includes a visual float for easy reading of the liquid level.

10. The flow metering insert according to claim 9, wherein, The flow rate increment, indicated by the markings on the scale, changes when it is above the liquid level or height in the flow indication channel corresponding to the height of the orifice in the exhaust channel.

11. The flow metering insert according to any one of the preceding claims, wherein, The indicating chamber includes a restricted inlet such that the maximum size of the inlet is less than 0.5 mm.

12. The flow metering insert according to claim 11, wherein, The restricted inlet of the indicating chamber is positioned in use below (i) the orifice of the flow resistance passage; and (ii) the lower end of the exhaust passage.

13. The flow metering insert according to any one of the preceding claims, wherein, The outlet of the main liquid flow channel includes multiple ribs.

14. The flow metering insert according to any one of the preceding claims, wherein, The flow resistance passage and / or flow indication passage and / or venting passage are partially defined by one or more first grooves and / or open channels in the surface of the insert, such that when the insert is inserted into the dripping chamber, the flow resistance passage and / or flow indication passage and / or venting passage are formed between the insert and the wall of the dripping chamber.

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