Controlled dosing of cryogenic fluid

Abstract

Aseptic dosing head (2, 60) for cryogenic fluid, comprising a reservoir (10) for cryogenic fluid connected to a metering outlet (24); a metering valve stem (30) extending through the cryogenic fluid reservoir and having a lower distal end designed to selectively open and close the metering outlet; an actuator (40) which is attached to an upper end of the metering valve stem (30) and is operable to move the metering valve stem to open and close the metering outlet (24); a seal (42) extending around the metering valve stem and separating the cryogenic fluid reservoir (10) from a cavity (44) between the seal and the actuator, the seal providing an airtight seal during operation; and a controller (50) that can be actuated to perform a head tightness test, including pressurizing the cavity (44) with a pressure higher than a pressure inside the reservoir (10) to check for leaks past the seal (42); and pressurizing the reservoir (10) to check for leaks from the cryogenic fluid reservoir.

Description

PRIORITY CLAIM

[0001] This application claims priority under 35 USC § 119(e) over US patent application serial no. 18 / 425,621, filed on January 29, 2024, and US patent application serial no. 63 / 623,393, filed on January 22, 2024, the entire contents of which are hereby incorporated by reference. TECHNICAL AREA

[0002] This invention relates to systems and methods for delivering controlled doses of a cryogenic liquid, such as liquid nitrogen. BACKGROUND

[0003] In some processes, it is important to dispense a known quantity of a cryogenic liquid. For example, liquid nitrogen canisters are dispensed into containers that are then immediately sealed in a beverage packaging line, so that after sealing, evaporating nitrogen pressurizes the container. In this process, the quantity of liquid dispensed must be carefully controlled. If too little cryogenic liquid is dispensed, the container may collapse under significant force. If too much liquid nitrogen is dispensed, excessive pressure will build up in the container, causing it to deform or rupture. Even when cryogenic liquid (usually nitrogen) is supplied to the container as an inert gas source, rather than to pressurize it, the dispensing of the cryogen must be reliable and consistent, without gaps or fluctuations.

[0004] Controlling the dispensed quantity or dose of liquid nitrogen can be challenging, especially when doses need to be administered rapidly, as is the case in a high-speed can or bottle filling line. The significant density change resulting from liquid evaporation means that devices dispensing a predetermined volume of liquid, such as valves, will not provide consistent amounts of cryogen unless the vapor / liquid state of the liquid is controlled.

[0005] Providing controlled doses of a cryogenic fluid under aseptic conditions involves other considerations, such as how to ensure that the dispensing equipment and the cryogen itself are as free from contamination or sterile as possible. Sterilizing the dispensing equipment can be challenging. SUMMARY

[0006] According to one aspect of the invention, an aseptic dosing head for cryogenic fluid comprises a cryogenic fluid reservoir connected to a dosing outlet, a dosing valve stem extending through the cryogenic fluid reservoir and having a lower distal end designed to selectively open and close the dosing outlet, and an actuator attached to an upper end of the dosing valve stem and actuated to move the dosing valve stem to open and close the dosing outlet.

[0007] In some embodiments, the actuator is electromagnetic.

[0008] In some embodiments, the dispensing button also features a seal that extends around the dispensing valve stem and separates the cryogenic fluid reservoir from a cavity between the seal and the electromagnetic actuator. The seal provides an airtight seal during operation.

[0009] In many examples, the head features a controller which may be located at some distance from the head but is nevertheless operable to perform a head tightness test, including pressurizing the cavity with a pressure higher than the pressure inside the reservoir to check for leaks past the seal, and pressurizing the reservoir to check for leaks from the cryogenic fluid reservoir.

[0010] In some cases, the controller can also be operated to sterilize the head by means of a process, including the introduction of a pressurized sterilization fluid into the reservoir while a gas is introduced into the cavity at a counter-pressure, thereby keeping the dosing outlet in a closed state during sterilization.

[0011] In some cases, the controller sequences valves to sterilize the head and introduces a pressurized liquid into the reservoir, while simultaneously pressurizing the non-aseptic cavity of the dosing head, thus keeping the dosing outlet in a closed state during sterilization.

[0012] The pressurized sterilization fluid can be, for example, steam.

[0013] In some cases, the controller is designed to perform the head tightness test both before and after sterilization of the head.

[0014] In some embodiments, the seal comprises a diaphragm attached to the metering valve stem. In some examples, the metering valve stem has both a lower valve stem section located below the diaphragm and an upper valve stem section located above the diaphragm and connected to the lower valve stem section by a threaded connection.

[0015] In some embodiments, the reservoir has a tube that extends from above a cryogenic liquid level to below the cryogenic liquid level and surrounds the metering valve stem.

[0016] In some cases, the cryogenic fluid reservoir is contained within a housing that connects the metering outlet to the electromagnetic actuator. The housing and metering valve stem are preferably made primarily of materials with coefficients of thermal expansion that differ by less than one percent. In some examples, both the housing and the metering valve stem are made of stainless steel.

[0017] In some embodiments, the reservoir includes a supply line for cryogenic fluid, which is filled with cryogenic fluid during operation and extends from a primary cavity of the reservoir to the metering outlet.

[0018] In some examples, the electromagnetic actuator is a servo motor. The servo motor may, for example, have an encoder that provides feedback to the controller regarding the position of the valve stem.

[0019] In some cases, the electromagnetic actuator can be controlled to change the distance and duration of the metering valve stem's displacement. This control can be achieved by modifying the desired target displacement and the timing values ​​of the actuator control signal. The electromagnetic actuator can also be controlled to change the metering valve stem's rest position relative to the metering outlet, for example, by changing the zero position of the valve stem displacement control.

[0020] Some embodiments also include a metering outlet gas flow valve that is controllable to introduce a flow of sterile gas from a pressurized source to the metering outlet to suppress frost accumulation. The metering outlet gas flow valve may be controllable to open when the electromagnetic actuator is not operating, for example, to deliver a dose of cryogenic fluid. The metering outlet gas flow valve may have a fixed bypass opening that allows a continuous flow of sterile gas to the metering outlet when the electromagnetic actuator is operating to deliver a dose of cryogenic fluid, and it may be arranged to introduce the flow of sterile gas to a portion of the metering outlet that is open to atmospheric pressure.

[0021] In some cases, the lower distal end of the metering valve stem has a thermoplastic cap that engages in a seat of the metering outlet.

[0022] Another aspect of the invention relates to a method for sterilizing a dosing head for cryogenic liquid, wherein the method comprises performing a system leak test by pressurizing a first cavity between a dosing valve stem seal and an electromagnetic dosing actuator and a second cavity on an opposite side of the dosing valve stem seal to check for system leaks, then checking for leaks past the seal by reducing the pressure in the second cavity and, with the pressure reduced in the second cavity, monitoring the pressure in the first cavity over a predetermined period of time.In response to a successful seal leak test, a sterilizing fluid is introduced into the second cavity and maintained in the second cavity under conditions that cause sterilization of the second cavity and a metering valve stem extending from the metering valve stem seal to a metering outlet for cryogenic fluid, while maintaining sufficient pressure in the first cavity to keep the metering valve stem seated at the metering outlet for cryogenic fluid.

[0023] In some cases, the seal leak test and the second cavity leak test are both performed before and after the introduction and maintenance of the sterilization fluid in the second cavity.

[0024] At least some embodiments of the invention can provide a particularly high aseptic dispensing rate. This can be achieved at least partially by enabling the use of a high-speed electromagnetic actuator under conditions that protect the actuator during sterilization.

[0025] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the following description. Other features, subject matter, and advantages of the invention will become apparent from the description, the drawings, and the claims. DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic diagram of a first embodiment of a dispensing system for cryogenic fluid for controlled dosing of cryogenic fluid. Fig. Figure 2 is a schematic diagram of a second embodiment of a cryogenic fluid delivery system for controlled dosing of cryogenic fluid. Fig. Figure 3 is a flowchart of a pressure test sequence. Fig. Figure 4 is a flowchart of a sterilization procedure including pressure test sequences.

[0026] Identical reference symbols in the different drawings indicate identical elements. DETAILED DESCRIPTION

[0027] Firstly, referring to Fig. Cryogen is supplied from a pressurized source to the aseptic dosing head 2 for cryogenic liquid and travels through a vacuum-jacketed pipeline 3, through a controllable inlet valve 4, and into a phase separation reservoir 10. The filling valve 4 can be controlled to ensure that the incoming cryogen is substantially liquefied. A sterile filter is located in the pipeline 3 upstream of the inlet valve 4, preventing unwanted particles from entering the reservoir. As the cryogen two-phase mixture flows into the reservoir 10, the gas phase is vented to the atmosphere through the vent line 6. The liquid phase collects in the reservoir 10 and is maintained at a constant level by controlling the valve 4 in response to a level sensor 14.Liquid flows freely by gravity down the feed line 16, which is an extension of the reservoir 10, to a metering valve 20. The pressure head at the bottom of the metering valve is controlled by regulating the cryogenic liquid level in the reservoir. The entire reservoir, including the feed line 16, is enclosed in a vacuum insulation chamber 22 to minimize heating.

[0028] The metering valve 20 is controlled to dispense discrete doses 22 of a cryogenic liquid, such as liquid nitrogen, from the metering outlet 24, which is arranged such that each dispensed dose 22 falls into a container 26 passing beneath the outlet. The valve 20 can be cycled at a high speed to dispense discrete doses 22 at a rate of, for example, up to 2,000 doses per minute, with each dose falling into its respective container. Each dose can be, for example, between 0.01 and 1.0 ml of cryogenic liquid. Each container moves to a sealing station immediately after dispensing.

[0029] The metering valve 20 has a valve stem 30 that cycles vertically to seat against and lift from a valve seat 32 at the metering outlet, thereby closing and opening the outlet. The stem is made of stainless steel with a thermoplastic tip to provide a sealing surface. When the outlet is open, cryogenic fluid is forced through the outlet by static pressure in the reservoir, determined by the fluid level. The valve seat is a surface of the outlet nozzle that can define a fixed dispensing orifice with a diameter of, for example, 0.065 inches (in some cases, with a diameter of 0.015 to 0.12 inches). The valve stem 30 is cycled by an electromagnetic linear actuator 40, which pushes and pulls the valve stem in response to a controlled electromagnetic force.A diaphragm 42 forms a seal that extends around the metering valve stem and separates the cryogenic fluid reservoir from a cavity 44 located between the diaphragm and the electromagnetic actuator 40. The diaphragm provides an airtight, annular seal, with an inner section of the diaphragm attached to the valve stem and an outer section of the seal attached to the surrounding structure, for example, by being captured at the inner end of a fitting that holds the actuator. In this example, the valve stem has an upper section attached to the actuator and a lower section extending to the valve seat. The two sections are threaded together on the diaphragm. The diaphragm flexes during each actuation cycle of the valve stem, allowing the stem to move vertically up to approximately 0.1 in (2.5 mm) for a full stroke.The diaphragm 42 can, for example, be EPDM-molded over a core of text material. During operation, the actuator 40 can be controlled to modulate the amount of lift of the valve stem and to change the opening and closing rate of the metering outlet, thereby modifying the metering volume and dispensing parameters as needed for optimal dosing. The metering volume can be controlled, for example, based on a measured tank pressure downstream of the capping station. Changing the metering parameters by controlling the linear actuator eliminates the need to shut down the line to change nozzle sizes.

[0030] In this example, the linear actuator 40 is a linear servo motor (electric cylinder) with an integrated encoder, a resolution of 5 µm, an operating voltage of 48 VDC, a maximum stroke of 10 mm, and a peak output force of 100 N. Suitable actuators are commercially available. Such an actuator is precisely controlled by pulse width modulation.

[0031] A metering outlet gas flow valve 34 can be controlled to introduce a flow of sterile dry gas from a pressurized source (not shown) to the metering outlet to aid in suppressing frost buildup at the metering outlet. The metering outlet gas flow valve is preferably controlled to open when the electromagnetic actuator is not operating to dispense a dose of cryogenic fluid and to close during metering. The metering outlet gas flow valve 34 has a fixed bypass orifice that allows a continuous flow of sterile gas to the metering outlet when the electromagnetic actuator is operating to dispense a dose of cryogenic fluid. In this way, a small flow of sterile gas always flows from the outlet to keep it clean and frost-free, and a high flow of sterile gas flows during periods without metering.As can be seen, the metering outlet gas flow valve is arranged to introduce the flow of sterile gas to a section of the metering outlet that is open to atmospheric pressure. A heated enclosure plate 36 at the outlet works in combination with the purge gas from valve 34 to maintain warm, ice-free surfaces during the metering of the cryogenic liquid.

[0032] Aseptic dispensing necessitates that the dispensing system be sterilized at regular intervals. This sterilization typically involves introducing high-temperature steam (e.g., 250°F) onto all internal surfaces normally exposed to the cryogen (either liquid or gas) downstream of the filling valve, at a pressure of approximately 30 psi, and maintaining these temperatures and pressures for a sufficient period to kill any bacteria and pathogens on the surfaces. One sterilization cycle is described below. To protect the membrane 42 during sterilization, a non-aseptic gas is introduced into the cavity 44 by controlling the counter-pressure valve 46, thereby equalizing at least most of the steam pressure in the reservoir to prevent the valve stem from disengaging from the valve seat until desired.In pneumatic systems, the pneumatic metering valve actuator will generally be able to develop sufficient downward force to maintain the valve seat during sterilization. Pressurizing the cavity 44 allows the use of electromagnetic actuators, which generally do not provide sufficient axial force to compensate for steam pressures.

[0033] Before performing a sterilization cycle, the integrity of the membrane 42 must be checked. Otherwise, high-temperature steam could damage the linear actuator. To check the membrane integrity, the cavity 44 can be pressurized to a test pressure above any pressure in the reservoir, and the cavity pressure can be monitored over a predetermined time interval to confirm that any leaks past the membrane are negligible. This membrane test can be part of a comprehensive head leak test in which both the cavity 44 and the reservoir are pressurized to check for leaks through any part of the aseptic section, and the reservoir pressure is then released while maintaining pressure in the cavity 44 to perform the membrane integrity test.

[0034] Aseptic dispensing also requires the mechanical components of the system to withstand extreme temperature changes, ranging from -320°F liquid nitrogen temperatures during operation to +250°F steam temperatures during sterilization. Such large temperature changes can cause significant problems due to thermal expansion. Given that the dispensing valve stem in an aseptic system can be up to 30 inches long, careful attention must be paid to avoiding problems caused by changes in the overall length of the valve stem due to thermal expansion. For example, the structure connecting the dispensing outlet to the linear actuator should be made of materials with a net coefficient of thermal expansion that is the same as, or substantially the same as, that of the valve stem.Preferably, the housing and the metering valve stem are primarily made of materials with coefficients of thermal expansion that differ by less than one percent. In this example, such a structure is also made of stainless steel. Additionally, a locating signal can be sent to the linear actuator after the valve stem has been immersed in cryogenic liquid for a period of time.

[0035] A controller 50 controls the various valves for performing pressure tests and running a sterilization cycle. This can be the same controller that also controls the linear actuator during operation. At the start of a diaphragm pressure test, the controller opens the backpressure valve 46 until the pressure in the cavity 44, measured by the cavity pressure sensor 52, exceeds the pressure in the reservoir 10 below the diaphragm, measured by the valve pressure sensor 54, by a fixed amount, such as 10 psi. The valve 46 is then closed, and the cavity pressure is monitored for a fixed time interval, such as two minutes. If the cavity pressure drops by more than a predetermined amount, such as 3 psi, over the time interval, the controller sends a warning message indicating that the diaphragm pressure test has failed, and the system undergoes maintenance.

[0036] Once the membrane test is complete, the controller 50 can also perform a full system leak test. With the vapor separator outlet valve 56 closed, the valve stem seated, and the reservoir vent line 6 closed (by a vent valve not shown), the controller pressurizes both the reservoir 10 and the cavity 44 by controlling valves 4 and 46 until the pressures at sensors 52 and 54 are both within a predetermined pressure range. Valves 4 and 46 are then closed, and the pressure at sensor 54 is monitored over a set time interval. If the reservoir pressure drops by more than a predetermined amount, such as 3 psi, over the time interval, the controller sends a warning message that the system leak test has failed, and the system is serviced. The membrane pressure test and the system leak test are normally both performed before and after system sterilization.

[0037] This sequence of these two tests is shown in the flowchart of Fig. Figure 3 shows the process. At the initiation of the pressure test sequence, the controller first closes open valves 102, then opens the backpressure valve 46 and the inlet valve 104, and starts a 30-second timer 106 while the main reservoir is pressurized in parallel with the cavity 44. When the timer reaches 30 seconds, the backpressure valve 46 and the inlet valve 4 are closed 108, and a 2-minute timer 110 is started. At the end of the two minutes, the reservoir pressure is checked at pressure sensor 54 112. If the pressure has dropped by more than 3.0 psi during the two minutes, a signal 114 is sent indicating a failure of the pressure test. Otherwise, valves 56 and 64 are opened to release the pressure from the reservoir 116, while the cavity 44 remains pressurized, and a third timer 118 is started.After two minutes, the pressure in cavity 44 is checked (120), and if the cavity pressure has fallen below a predetermined setpoint, a signal is sent (122) indicating a failure of the membrane integrity test. Otherwise, the pressure test is successfully completed (124).

[0038] For sterilization of the system, the controller 50 controls the inlet valve 4, through which pressurized steam (or another sterilizing medium) is introduced into the reservoir for sterilization, and the outlet valve 56, through which the steam is removed via a steam separator 58 after sterilization. As described above, the controller simultaneously pressurizes the cavity 44 with inert gas during sterilization by controlling the valve 46 to help equalize stresses on the diaphragm and to hold the valve stem in its seat. The reservoir vent valve (not shown) is also kept closed during sterilization. The outlet valve 56 may remain at least partially open during the filling of the reservoir with steam to ensure a flow of sterilizing steam into the metering valve and to the diaphragm.The controller can monitor the temperature at various points in the system to confirm that sterilization temperatures and times have been achieved before venting through the outlet valve. Sterilization of the dosing outlet can be performed by lifting the valve stem under steam conditions and allowing pressurized steam to be vented through the outlet.

[0039] The sterilization sequence is shown schematically in Fig. 4. At initiation 200, approximately at the end of a dosing run, cryogen is emptied from the system 202 by opening the dosing outlet 24 with the fill valve 4 closed, and maintaining this configuration until the level sensor 14 indicates an empty reservoir for a predetermined period, such as 5 minutes. Next, the fill valve 4 is opened to allow a flow of dry gas, and the reservoir is heated to a temperature above -100°F 204. Once an elevated reservoir temperature has been confirmed, the pressure test discussed above 100 is initiated. Upon successful completion 124 of the pressure test, the valve 4 is opened to allow a flow of heated sterilizing fluid, such as steam 206.The various valves leading from the reservoir are cycled to ensure that the entire reservoir is exposed to sufficiently heated steam, while the cavity 44 is adequately pressurized via valve 46 to prevent a high pressure differential across the membrane 42. During this sterilization step, the dispensing outlet 24 can be cleaned, either by introducing a sterilizing fluid through valve 34 or by sterilizing the outlet from below. The reservoir temperature is monitored until it exceeds a predetermined threshold, approximately 250°F, for a minimum period of time, approximately 30 minutes, to ensure sterilization of all internal surfaces.Following sterilization, the sterilization fluid is flushed from the system 210 using a dry stream of sterile gas through inlet valve 4, with the other valves in the system being cycled as needed to ensure the entire system is flushed. After flushing, the pressure test sequence is restarted 100 to confirm that the system is sealed and ready for further dispensing. A dry gas stream is also provided through the dispensing outlet valve 34. Once the pressure tests have been successfully completed 124, the reservoir is filled with cryogenic fluid to a desired level 126, and dispensing can resume.

[0040] The controller 50 is connected to a user interface (not shown) that allows the operator to set parameters such as dosing duration and valve stem stroke, and to switch the dosing on and off. The controller 50 also receives input from various sensors, such as the level sensor 14, the pressure sensors 52 and 54, and various temperature sensors. To control the electromagnetic actuator 40, the controller 50 also receives a signal indicating the presence of a container to be dosed, such as a single pulse from a container sensor (not shown), and a signal from an encoder embedded in the electromagnetic actuator that responds to a displacement of the valve stem. For example, there can be 300 to 1500 encoder pulses per container dosing cycle.The controller 50 also has outputs for controlling the various valves, such as the inlet valve 4, the purge gas valve 34, the back pressure valve 46, the outlet valve 56 and the vent valve 64.

[0041] Referring to Fig. 2. The aseptic dosing head 60 for cryogenic liquid has a similar function to the one in Fig. The system shown in Figure 1 is based on the system shown in Figure 1, but the cryogen reservoir is concentric around the valve stem 30, which extends from the diaphragm 42 into the reservoir. The reservoir is surrounded by a tube 62 that extends below the free surface of the cryogenic fluid 70 in the reservoir. In this example, the reservoir vent valve 64 is shown. As in the example of Fig.1. All valves are controlled by the controller 50 to perform the membrane and leak tests discussed above, as well as to sterilize the aseptic space and surfaces. This example also shows a cover 66, which is controlled to pivot to cover the dosing outlet during sterilization and when the system is not in use. The cover defines a small hole through which condensate can drip from the dosing outlet cavity during sterilization. Some system components, such as a level switch or a sensor coupled to the filling valve 4, as well as various pressure and temperature sensors (except for a temperature sensor 68 in the steam vent line), are not shown for clarity.

[0042] While several examples have been described for illustrative purposes, the above description is not intended to limit the scope of the invention, which is defined by the scope of the appended claims. There are and will be other examples and modifications within the scope of the following claims. For example, although a diaphragm with a fixed edge is described as a seal along the metering valve stem, a sliding seal (such as an O-ring or a lip seal that slides along the stem surface) may be used, but additional precautions should be taken to ensure that the entire valve stem surface exposed to the aseptic cavity during use is properly sterilized. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 18 / 425,621

[0001] US 63 / 623,393

[0001]

Claims

[1] Aseptic dosing head (2, 60) for cryogenic liquid, comprising a reservoir (10) for cryogenic liquid communicating with a metering outlet (24); a metering valve stem (30) extending through the cryogenic liquid reservoir and having a lower distal end configured to selectively open and close the metering outlet; an actuator (40) attached to an upper end of the metering valve stem (30) and operable to move the metering valve stem to open and close the metering outlet (24); a seal (42) extending around the metering valve stem and separating the cryogenic liquid reservoir (10) from a cavity (44) between the seal and the actuator, the seal providing an airtight seal during operation; and a controller (50) operable to perform a head leak test, including pressurizing the cavity (44) to a pressure greater than a pressure within the reservoir (10) to test for leaks past the seal (42); and pressurizing the reservoir (10) to test for leaks from the cryogenic fluid reservoir. [2] The aseptic cryogenic liquid dosing head of claim 1, wherein the controller (50) is also operable to perform a sterilization cycle of the head (2, 60) comprising introducing a pressurized sterilizing liquid into the reservoir while introducing a gas at a counter pressure into the cavity, thereby maintaining the dosing outlet (24) in a closed state during sterilization. [3] The aseptic cryogenic liquid dispensing head of claim 2, wherein the pressurized sterilizing liquid comprises steam. [4] The aseptic cryogenic liquid dispensing head of claim 2, wherein the controller (50) is configured to perform the head leak test both before and after performing the sterilization cycle. [5] The aseptic cryogenic liquid dosing head of claim 1, wherein the seal comprises a membrane (42). [6] The aseptic cryogenic liquid dosing head of claim 5, wherein the dosing valve stem (30) comprises a lower valve stem portion disposed below the diaphragm (42) and an upper valve stem portion disposed above the diaphragm and connected to the lower valve stem portion by a threaded connection. [7] The aseptic cryogenic liquid dosing head (60) of claim 1, wherein the cryogenic liquid reservoir (10) is contained within a housing connecting the dosing outlet (24) to the actuator (40), and wherein the housing and the dosing valve stem (30) are primarily made of materials having coefficients of thermal expansion that differ by less than one percent. [8] Aseptic dosing head for cryogenic liquid according to claim 7, wherein both the housing and the dosing valve stem (30) are made of stainless steel. [9] The aseptic cryogenic liquid dosing head of claim 1, wherein the reservoir (10) comprises a tube (62) extending from above a cryogenic liquid level to below the cryogenic liquid level and surrounding the dosing valve stem (30). [10] An aseptic cryogenic liquid dosing head according to claim 1, wherein the reservoir comprises a cryogenic liquid supply line (16) which, in use, is filled with cryogenic liquid and extends from a primary cavity of the reservoir (10) to the dosing outlet (24). [11] The aseptic cryogenic liquid dosing head of claim 1, wherein the actuator (40) comprises a servo motor. [12] The aseptic cryogenic liquid dosing head of claim 1, wherein the actuator (40) is controllable to change a distance and duration of displacement of the dosing valve stem. [13] The aseptic cryogenic liquid dosing head of claim 1, wherein the actuator is controllable to change a rest position of the dosing valve stem (30) relative to the dosing outlet (24). [14] The aseptic cryogenic liquid dosing head of claim 1, further comprising a dosing outlet gas flow valve (34) controllable to introduce a flow of sterile gas from a pressurized source to the dosing outlet (24) to suppress frost accumulation. [15] The aseptic cryogenic liquid dosing head of claim 14, wherein the dosing outlet gas flow valve (34) is controllable to open when the actuator is not operating to dispense a dose of cryogenic liquid. [16] The aseptic cryogenic liquid dosing head of claim 14, wherein the dosing outlet gas flow valve (34) includes a fixed bypass orifice allowing continuous flow of sterile gas to the dosing outlet (24) when the actuator (40) is operating to dispense a dose of cryogenic liquid. [17] The aseptic cryogenic liquid dosing head of claim 14, wherein the dosing outlet gas flow valve (34) is arranged to introduce the flow of sterile gas to a portion of the dosing outlet open to atmospheric pressure. [18] The aseptic cryogenic liquid dosing head of claim 1, wherein the lower distal end of the dosing valve stem (30) includes a thermoplastic cap engaging a seat of the dosing outlet.

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