Fluid control system

Abstract

A fluid control system (10) for a pilot-operated pressure regulating valve (4) comprises a first conduit (12), defining a first flow path, and a second conduit (14), defining a second flow path. The second conduit (14) is parallel to the first conduit (12) and comprises a restriction aperture (70). A variable flow restrictor (20) within the second conduit (14) is arranged to selectively vary a cross-sectional area of the restriction aperture (70). The first conduit (12) comprises a converging portion (48), for reducing the pressure of fluid flowing through the converging portion (48) to an intermediate pressure, and a diverging portion (54). The system (10) also includes a control fluid port (22) for connecting to a control volume (34) of the pressure regulating valve (4), the control fluid port (22) being configured to receive fluid at the intermediate pressure from the first conduit (12).

Description

[0001] 174699 / 01

[0002] Fluid Control System

[0003] The present invention relates to a fluid control system for a pilot-operated pressure regulating valve.

[0004] In fluid flow systems such as pipes and conduits, which can be found in many different fluid regulation and distribution networks across various industries, there is a need to regulate the pressure or flow rate in a fluid flow stream. Pressure regulating valves often comprise a valve member that opens and closes a valve aperture in dependence on the difference between a control pressure applied to the valve member and an upstream or downstream pressure.

[0005] Pilot valves may be used to regulate the control pressure provided to pressure regulating valves. A pilot valve may include a pressure sensing component (e.g. a piston or diaphragm) and a poppet assembly which is moved between an open position, in which fluid may flow through the pilot valve, and a closed position, in which the flow of fluid is restricted. The pressure upstream or downstream of the pressure regulating valve acts on the pressure sensing component of the pilot valve against the force of a loading spring. The force exerted by the loading spring on the pressure sensing component may be adjusted by compressing or decompressing the loading spring. This determines the set target pressure, or setpoint, of fluid flowing out of the pilot valve.

[0006] The pressure of the control fluid applied to the valve member of the pressure regulating valve (i.e. the control pressure) may be derived from the pressure upstream of the pressure regulating valve. Conventional fluid control systems are used to provide pressure to the control volume of the pressure regulating valve, and they may comprise a component for reducing the pressure of the control fluid before it is provided to the pressure regulating valve, e.g, an orifice.

[0007] The configuration of the fluid control system may influence the stability and accuracy of the pressure regulating valve, and it is typically desirable for a fluid control system to be suitably tuned for a particular application in order to enable reliable operation of the pressure regulating valve. However, conventional fluid control systems either require entire components to be replaced in order to tune the system for a particular application, or rely on adjustable components that are complex and difficult to manufacture, particularly for use in small scale systems.

[0008] The present invention seeks to provide an improved fluid control system.

[0009] When viewed from a first aspect, the present invention provides a fluid control system for a pilot-operated pressure regulating valve, the fluid control system comprising: an inlet port for receiving fluid at an upstream pressure from an upstream side of the pressure regulating valve; an outlet port for connecting to an inlet of a pilot valve for operating the pressure regulating valve; a first conduit defining a first flow path connecting the inlet port and the outlet port; and a second conduit defining a second flow path connecting the inlet port and the outlet port, the second flow path comprising a restriction aperture, wherein the second conduit is arranged in parallel with the first conduit; wherein the first conduit comprises: a converging portion for reducing the pressure of fluid flowing through the converging portion from the upstream pressure to an intermediate pressure, wherein the cross-sectional area of the first flow path through the converging portion decreases in a downstream direction; and a diverging portion for increasing the pressure of fluid flowing through the diverging portion from the intermediate pressure to an outlet pressure, wherein the cross-sectional area of the first flow path through the diverging portion increases in the downstream direction; wherein the system further comprises: a control fluid port for connecting to a control volume of the pressure regulating valve, wherein the control fluid port is configured to receive fluid at the intermediate pressure from the first conduit; and a variable flow restrictor within the second conduit, wherein the variable flow restrictor is arranged to selectively vary a cross-sectional area of the restriction aperture of the second flow path.

[0010] When viewed from a second aspect, the present invention provides a pressure regulating system comprising: a pressure regulating valve comprising: a housing defining a control volume and a valve aperture; and a valve member movably mounted on the housing and arranged to move reciprocally to selectively open and close the valve aperture, thereby controlling a flow of fluid through the valve aperture, wherein the valve member is acted on by a control pressure in the control volume to control the position of the valve member; a pilot valve for operating the pressure regulating valve; and a fluid control system; wherein the fluid control system comprises: an inlet port connected to an upstream side of the pressure regulating valve so as to receive fluid at an upstream pressure; an outlet port connected to an inlet of the pilot valve; a first conduit defining a first flow path connecting the inlet port and the outlet port; and a second conduit defining a second flow path connecting the inlet port and the outlet port, the second flow path comprising a restriction aperture, wherein the second conduit is arranged in parallel with the first conduit; wherein the first conduit comprises: a converging portion for reducing the pressure of fluid flowing through the converging portion from the upstream pressure to an intermediate pressure, wherein the cross-sectional area of the first flow path through the converging portion decreases in a downstream direction; a diverging portion for increasing the pressure of fluid flowing through the diverging portion from the intermediate pressure to an outlet pressure, wherein the cross-sectional area of the first flow path through the diverging portion increases in the downstream direction; wherein the fluid control system further comprises: a control fluid port connected to the control volume of the pressure regulating valve, wherein the control fluid port is configured to receive fluid at the intermediate pressure from the first conduit; and a variable flow restrictor within the second conduit, wherein the variable flow restrictor is arranged to selectively vary a cross-sectional area of the restriction aperture of the second flow path.

[0011] Thus, the present invention provides a flow control system that includes a first conduit, comprising a converging portion and a diverging portion, and a second conduit in parallel with the first conduit that includes a variable flow restrictor.

[0012] The converging portion of the first conduit acts to reduce the pressure of the fluid provided to the control volume, relative to the upstream pressure. Thus, the converging portion may help to ensure that there is a pressure differential across the valve member of the pressure regulating valve when there is a flow of fluid through the fluid control system (which will occur when the pilot valve is not fully closed).

[0013] The magnitude of the maximum attainable pressure differential that the fluid control system can generate (i.e. the maximum attainable difference between the upstream pressure and the pressure within the control volume) may influence the accuracy and stability of the pressure regulating valve. A small pressure differential may increase the stability of the pressure regulating valve at the expense of accuracy, as the actuating force provided by the pressure differential may be insufficient to move the valve member. In contrast, a large pressure differential may increase the accuracy of the pressure regulating valve at the expense of stability.

[0014] The diverging portion of the first conduit acts to increase the pressure from the intermediate pressure to the outlet pressure, meaning that the converging portion and the diverging portion in combination may provide a pressure amplifier function.

[0015] The pressure regulating valve may be configured to reduce the pressure of fluid flowing through the pressure regulating valve from the upstream pressure to a downstream pressure. The provision of a diverging portion and a converging portion as described above may allow the intermediate pressure (and thus the pressure provided to the control volume of the pressure regulating valve) to be less than or equal to the downstream pressure. Typically, the smaller the pressure drop from the upstream side to the downstream side of the pressure regulating valve, the greater the differential that may be required between the control pressure in the control volume and the downstream pressure in order for the pressure regulating valve to open fully. Thus, by providing diverging and converging portions that enable the control pressure to be reduced significantly relative to the downstream pressure, the minimum required differential pressure across the pressure regulating valve to open the pressure regulating valve fully may be substantially reduced, which may improve the reliability of the pressure regulating valve.

[0016] The accuracy and / or the stability of the pressure regulating valve may be adjusted by increasing or reducing the flow capacity of the flow control system relative to the flow capacity of the pilot valve.

[0017] It will be appreciated that the rate of flow of fluid along the second flow path may be varied by varying the cross-sectional area of the restriction aperture. By providing the first and second conduits in parallel, the total flow capacity of the flow control system can be varied using the variable flow restrictor, without requiring the timeconsuming and cumbersome replacement of components, whilst retaining the beneficial pressure drop and pressure recovery provided by the converging and diverging portions of the first conduit.

[0018] In some embodiments, the first conduit comprises a throat defined between the converging portion and the diverging portion, wherein the throat defines the narrowest cross-sectional area of the flow path through the first conduit. The diameter of the throat may be between 1 mm and 5mm, e.g. between 1.5 mm and 2.5 mm, e.g. approximately 1.7 mm. The control fluid port may be configured to receive fluid from the first conduit at or adjacent the throat. The control fluid port may be configured to receive fluid from the first conduit at the vena contracta of the fluid flow through the first conduit, during normal operation. The length of the throat may be between 0.5 mm and 1.5 mm, e.g. between 0.75 and 1.25 mm, e.g. approximately 1 mm. The fluid control system may comprise one or more pressure taps connecting the first conduit and the control fluid port. The one or more pressure taps may extend radially from the first conduit. In some embodiments, the total cross-sectional area of the one or more pressure taps (i.e. the sum of the cross-sectional areas of each pressure tap in a plane perpendicular to the direction of fluid flow through the pressure tap) is greater than or equal to the cross-sectional area of the throat (in a plane perpendicular to the direction of fluid flow through the throat).

[0019] The converging portion of the first conduit may comprise an orifice defining a stepchange reduction in cross-sectional area. In some embodiments, the converging portion of the first conduit comprises a converging nozzle defining at least a portion of the reduction in the cross-sectional area. The converging nozzle may define a uniform reduction in cross-sectional area along its length. The converging nozzle may converge at an angle of between 10° and 40°, e.g. between 15° and 30°, e.g. approximately 20° to the horizontal (i.e. the general direction of flow through the nozzle). The converging nozzle may define a reduction in cross-sectional area with an increasing or decreasing gradient along its length. A converging nozzle may have a higher discharge coefficient than an orifice defining a step-change reduction in cross-sectional area, meaning that the pressure loss through the nozzle may be lower.

[0020] The diverging portion of the first conduit may comprise a step-change increase in cross-sectional area. This may help to ensure, at sonic throat conditions, that supersonic expansion and pressure recovery in the diverging portion of the first conduit is limited, which may help to ensure that the point of minimum pressure is at or immediately adjacent the throat of the convergent portion of the first conduit at all conditions. As the location of the minimum pressure through the first conduit may thus be more reliably known (at or adjacent the throat), the connection between the control fluid port and the first conduit can be positioned (at or adjacent the throat) so as to tap off the minimum pressure as the intermediate pressure more reliably. The step-change increase in cross-sectional area may be positioned immediately upstream of the connection between the control fluid port and the first conduit.

[0021] In some embodiments, the diverging portion of the first conduit comprises a diverging nozzle defining at least a portion of the increase in cross-sectional area. The diverging nozzle may define a uniform increase in cross-sectional area along its length. The diverging nozzle may diverge at an angle that is shallower than that at which the converging nozzle converges. The diverging nozzle may diverge at an angle of between 1° and 20°, e.g. between 3° and 10°, e.g. approximately 5° to the horizontal (i.e. the general direction of flow through the nozzle). The diverging nozzle may define an increase in cross-sectional area with an increasing or decreasing gradient along its length. The diverging portion of the first conduit may comprise both a step-change increase in cross-sectional area and a diverging nozzle. The diverging nozzle may be located downstream of the step-change increase in cross-sectional area. The use of a diverging nozzle may allow a greater proportion of the upstream pressure to be recovered. This means that the intermediate pressure (and thus the pressure in the control volume) may be substantially lower than the downstream pressure, which may improve the reliability of the pressure regulating valve, as explained above.

[0022] The diverging portion may comprise a constant-area section, wherein the cross- sectional area of the constant-area section is constant along the length of the constant-area section. The constant-area section may be (e.g. immediately) downstream of the throat. The step-change increase in cross-sectional area may be defined between the throat and the constant-area section. The constant-area section may be located between the throat and the diverging nozzle. The diameter of the constant-area section may be between 2 mm and 10 mm, e.g. between 3 mm and 5 mm, e.g. approximately 3.4 mm. The diameter of the constant-area section may be approximately twice the diameter of the throat.

[0023] The length of the converging portion of the first conduit may be between 3mm and 15 mm, e.g. between 5 mm and 10 mm, e.g. approximately 6 mm. The length of the converging portion may be between 2.5 and 10 times the diameter of the throat, e.g. between 5 and 7 times, e.g. approximately 6 times the diameter of the throat.

[0024] The length of the diverging portion may be greater than the length of the converging portion. The length of the diverging portion of the first conduit may be between 10 mm and 40 mm, e.g. between 20 and 30 mm, e.g. approximately 25 mm. The length of the diverging portion may be between 5 and 25 times the diameter of the throat, e.g. between 10 and 20 times, e.g. approximately 15 times the diameter of the throat.

[0025] The control fluid port may be configured to receive fluid from the converging portion of the first conduit. In some embodiments, the control fluid port is configured to receive fluid from the diverging portion of the first conduit, e.g. from the constantarea section or the diverging nozzle.

[0026] The variable flow restrictor may comprise a needle valve. The variable flow restrictor may comprise a ball valve. In some embodiments, the variable flow restrictor is rotatably arranged within the second conduit such that the second flow path through the second conduit is defined between an outer surface of the variable flow restrictor and an inner wall of the second conduit. The restriction aperture may be defined between the outer surface of the variable flow restrictor and the inner wall of the second conduit. The second conduit may comprise a restrictor inlet and a restrictor outlet, wherein the restriction aperture is defined between the restrictor inlet and the restrictor outlet. The diameter of the restrictor inlet and / or the diameter of the restrictor outlet may be between 1 mm and 10 mm, e.g. between 2 mm and 5 mm, e.g. approximately 2.5 mm. The diameter of the restrictor inlet and / or the diameter of the restrictor outlet may be approximately twice the diameter of the throat of the first conduit.

[0027] The variable flow restrictor may be rotatable about its longitudinal axis. In some embodiments, the variable flow restrictor is freely rotatable, i.e. without being threadedly mounted. The variable flow restrictor may be axi-asymmetric about its axis of rotation such that the cross-sectional area of the restriction aperture in a plane parallel to the axis of rotation varies as the variable flow restrictor is rotated. It will be appreciated that the term axi-asymmetry is intended to exclude geometry that is completely invariant under rotation about a particular axis, but does include geometry having one or more orders of rotational symmetry about said axis.

[0028] The fluid control system may comprise a housing that defines one or more (e.g. all) of: the inlet port, the outlet port, the first conduit, the second conduit, and the control fluid port. The housing may comprise a monolithic component defining one or more (e.g. all) of the inlet port, the outlet port, the first conduit, the second conduit, and the control fluid port. The housing may define the one or more pressure taps. In some embodiments, the housing comprises one or more removable sections and a monolithic section, wherein the one or more removable sections are removably attachable to the monolithic section.

[0029] In some embodiments, the fluid control system comprises a filter between the inlet port and the first and second conduits. This may help to remove debris from the fluid flowing through the first and second conduits, which may help to avoid the system becoming clogged. The filter may be removably mounted within the housing. This may allow the filter to be cleaned and / or replaced with ease.

[0030] In some embodiments, the fluid control system comprises a removable insert defining at least the converging portion and the diverging portion of the first conduit. By providing the converging portion and the diverging portion in a removable insert, it will be appreciated that these portions may be more easily replaced (e.g. swapped for larger or smaller flow capacity components) if required.

[0031] The removable insert may be a monolithic component. This may help to improve the ease with which the converging portion and the diverging portion can be aligned within the housing, e.g. so as to align with the pressure tap(s) to the control fluid port. The removable insert may be made from any suitable material. In some embodiments, the removable insert is made from brass, stainless steel, or plastic. The removable insert may be receivable within the first conduit so that fluid flowing through the first conduit is directed through the converging portion and the diverging portion.

[0032] The variable flow restrictor may comprise a variable flow restrictor as described in WO 2022 / 043680. In some embodiments, the housing defines a bore that intersects the second conduit. The variable flow restrictor may be arranged within the bore. The variable flow restrictor may extend longitudinally along an axis that is coaxial with the longitudinal axis of the bore. The restriction aperture may be located at an intersection between the second conduit and the bore. The bore may extend into the housing to intersect the second conduit from an external surface of the housing. The bore may be a blind hole, e.g. extending into the housing to, or beyond, the depth of the second conduit. The bore may be a through hole extending through the whole depth of the housing. Arranging the variable flow restrictor within a through- bore may help to ensure that the variable flow restrictor is pressure balanced, which may improve the operation of the variable flow restrictor at higher pressures.

[0033] The variable flow restrictor may be axi-asym metric about its longitudinal axis. In some embodiments, the variable flow restrictor is axi-symmetric along the length of the variable flow restrictor apart from an axi-asym metric portion of the variable flow restrictor that is arranged to selectively vary the cross-sectional area of the restriction aperture. The restriction aperture may be defined between this axi- asymmetric portion of the variable flow restrictor and the housing.

[0034] The variable flow restrictor may comprise a restriction feature that is arranged to define the restriction aperture, e.g. such that movement of the restriction feature acts to vary the cross-sectional area of the restriction aperture. The restriction feature may provide the axi-asym metry of the variable flow restrictor.

[0035] The restriction feature may comprise a radial protrusion (e.g. a lobe) extending from the outer surface of the variable flow restrictor. In some embodiments, the restriction feature comprises a pair of diametrically opposed protrusions (e.g. lobes), each extending from the outer surface of the variable flow restrictor, e.g. in the direction of a radius of the variable flow restrictor. The restriction aperture may be defined between one or both of the protrusions and the inner wall of the housing. The restriction feature may comprise a pair of diametrically opposed spiral portions (e.g. thus resembling a tilde).

[0036] In some embodiments, the fluid control system comprises an actuator for adjusting the variable flow restrictor, i.e. for adjusting the cross-sectional area of the restriction aperture of the second flow path. The actuator may comprise a knob, wherein rotation of the knob causes the variable flow restrictor to rotate so as to vary the cross-sectional area of the restriction aperture. In some embodiments, the actuator is provided on an exterior surface of the housing of the flow control system. This may allow it to be operated easily by a user.

[0037] The actuator may comprise a display for providing an indication of the cross- sectional area of the restriction aperture (e.g. a scale from least restricted to most restricted, an estimated or measured flow rate, a cross-sectional area value). The display may comprise a dial and an indicator mark. The display may comprise an electronic display, e.g. an LCD display screen or an LED. This may allow a user to more easily determine the extent to which the restriction aperture is restricted.

[0038] The variable flow restrictor may be configured, in its most restrictive configuration, to reduce the cross-sectional area of the restriction aperture so as to substantially prevent the flow of fluid through the restriction aperture (and thus through the second conduit). The variable flow restrictor may be configured to vary the cross- sectional area of the restriction aperture so that the maximum flow rate of the fluid through the second conduit varies between 50% and 500% of the flow rate through the first conduit.

[0039] In some embodiments, the fluid control system comprises a control fluid conduit fluidly connecting the first conduit to the control fluid port. The control fluid conduit may be defined by the housing. In some embodiments, the fluid control system comprises a control-fluid variable flow restrictor within the control fluid conduit for selectively varying the cross-sectional area of a flow path through the control fluid conduit.

[0040] The control-fluid variable flow restrictor may comprise any or all of the features described herein with reference to the variable flow restrictor within the second conduit. For example, the control-fluid variable flow restrictor may comprise a restriction feature comprising a pair of diametrically opposed protrusions. The control-fluid variable flow restrictor may be located within a bore of the housing that intersects the control fluid conduit. The control-fluid variable flow restrictor and the variable flow restrictor within the second conduit may be the same design, or may be different.

[0041] The housing of the pressure regulating valve may comprise a mounting member on which the valve member is moveable mounted. The mounting member may be cylindrical. The valve member may comprise a sheath on the outside of the mounting member. The valve member may comprise an end cap that is arranged to open and close the valve aperture. The mounting member and the valve member may be arranged on the downstream side of the valve aperture. The housing may define a control fluid feed for introducing control fluid into the control volume to exert the control pressure on the valve member. The valve member may be moved by the difference between the upstream pressure and the control pressure. The fluid control system may be configured to generate a control pressure that is variable between a maximum that is substantially equal to the upstream pressure and a minimum that is substantially equal to or less than the downstream pressure. The pressure regulating valve may comprise a biasing member arranged to bias the valve member towards the valve aperture. The biasing member may be arranged within mounting member, e.g. within the control volume.

[0042] The pilot valve may comprise an inlet for receiving fluid from the flow control system and an outlet for outputting fluid to a downstream side of the pressure regulating valve. The pilot valve may comprise a pilot valve member configured to control the flow of fluid form the inlet of the pilot valve to the outlet of the pilot valve. The pilot valve may comprise a pressure sensing component arranged to be acted on by a sensed pressure. The sensed pressure may be the upstream pressure (i.e. the pressure upstream of the pressure regulating valve). The sensed pressure may be the downstream pressure (i.e. the pressure downstream of the pressure regulating valve). The pilot valve may comprise a loading arrangement, e.g. a loading biasing member, e.g. a loading spring, configured to exert a force on the pressure sensing component (i.e. the “setpoint” of the pilot valve). The force exerted by the loading arrangement may act on the pressure sensing component so as to oppose a force exerted on the pressure sensing component by the sensed pressure.

[0043] The upstream pressure may be between 0.35 and 100 bar, e.g. between 20 bar and 80 bar, e.g. approximately 50 bar. The downstream pressure may be between 0.2 bar and 70 bar, e.g. between 20 bar and 50 bar, e.g. approximately 35 bar.

[0044] It will be appreciated that the second aspect of the present invention may include any one or more or all of the optional features of the first aspect as discussed herein, as appropriate, and vice versa. Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0045] Figure 1 shows a schematic of a pressure regulating system including a fluid control system;

[0046] Figure 2 shows the fluid control system and pressure regulating valve of Figure 1 in more detail;

[0047] Figure 3 shows a more detailed cross-sectional view of the convergingdiverging component and the variable flow restrictor of the fluid control system of Figure 1 ; and

[0048] Figure 4 shows a cross-sectional view of the variable flow restrictor, in a plane perpendicular to the plane of the cross-section shown in Figure 3 and parallel to the second conduit.

[0049] Figure 1 shows a schematic of a pressure regulating system 2 comprising a pilot- operated pressure regulating valve 4.

[0050] The pressure regulating valve 4 is arranged to receive fluid at an upstream pressure from an inlet conduit 6, and is arranged to output fluid at a downstream pressure poutinto an outlet conduit 8.

[0051] The pressure regulating system 2 comprises a fluid control system 10. As will be described in more detail below, the fluid control system 10 comprises a first conduit 12 and a second conduit 14, arranged in parallel with the first conduit 12. The first and second conduits 12, 14 are arranged to receive fluid at the upstream pressure p±from the inlet conduit 6 and to output fluid to a pilot inlet conduit 16.

[0052] The fluid control system comprises a converging-diverging component 18 arranged within the first conduit 12 and a variable flow restrictor 20 arranged within the second conduit 14.

[0053] As fluid flows through the converging-diverging component 18, the fluid pressure is reduced from the upstream pressure p±to an intermediate pressure p3, and is subsequently increased to an outlet pressure p2, which is provided to the pilot inlet conduit 16. Fluid at the intermediate pressure p3is tapped off from the convergingdiverging component 18 to a control fluid conduit 22, which provides the fluid to a control volume of the pressure regulating valve 4 via a control-fluid variable flow restrictor 26 that is arranged within the control fluid conduit 22. The control-fluid variable flow restrictor 26 further decreases the pressure of the fluid, which is provided to the control volume at a control pressure p4. The control-fluid variable flow restrictor 26 is described in more detail below.

[0054] The pressure regulating system 2 further comprises a pilot valve 24 that is arranged to receive fluid from the pilot inlet conduit 16 at the outlet pressure p2. The output of the pilot valve 24 is in fluid communication with the outlet conduit 8, downstream of the pressure regulating valve 4.

[0055] Figure 2 shows a more detailed cross-sectional view of the fluid control system 10 and the pressure regulating valve 4 of Figure 1. The pilot valve 24 and the fluid connections between the fluid control system 10, the pilot valve 24, and the inlet and outlet conduits 6, 8 are shown schematically.

[0056] The pressure regulating valve 4 comprises a valve member 28 that is reciprocally mounted on the outer surface of a cylindrical housing 30 to open and close a valve aperture 32 defined in the inlet conduit 6. A control volume 34 is defined between the inner surface of the valve member 28 and the housing 30. The control volume 34 is arranged to receive fluid at the control fluid pressure p4from the control fluid conduit 22. The valve member 28 is moved by the difference between the intermediate pressure p3and the upstream pressure p±.

[0057] The fluid control system 10 comprises a housing 36 that defines the first conduit 12, the second conduit 14, and the control fluid conduit 22. The housing 36 further comprises an inlet port 38, in fluid communication with the inlet conduit 6, and an outlet port 40, in fluid communication with the pilot valve 24 via the pilot inlet conduit 16.

[0058] The fluid control system 10 further comprises a filter 42 arranged between the inlet port 38 and the first and second conduits 12, 14. Fluid from the inlet conduit 6 flows through the inlet port 38 and the filter 42 before splitting into parallel streams (i.e. first and second flow paths) through the first and second conduits 12, 14 respectively. The filter 42 helps to prevent debris from entering the first and second conduits 12, 14 and clogging the pressure regulating system 2. The first and second flow paths recombine in the pilot inlet conduit 16.

[0059] The housing 36 comprises a monolithic section 36a, a first removable section 36b, and a second removable section 36c. The first and second removable sections 36b, 36c are removably mountable to the monolithic section 36a.

[0060] The filter 42 is arranged within a cavity 44 that is defined in the monolithic section 36a of the housing 36. The first removable section 36a seals the cavity 44 when the first removable section 36a is mounted to the monolithic section 36a. The first removable section 36a can be removed from the monolithic section 36a so as to allow the filter 42 to be removed from the housing 36 (e.g. for cleaning or replacing).

[0061] The monolithic section 36a of the housing further defines a blind bore 46 within which the converging-diverging component 18 is located. The converging-diverging component 18 is machined from a single brass block (embodying a removable insert) and is removably mounted in the blind bore 46. The converging-diverging component 18 can be removed from the blind bore 46 when the second removable section 36b of the housing 36 is separated from the monolithic section 36a of the housing 36.

[0062] The second removeable section 36b defines the portion of the pilot inlet conduit 16 in which the parallel streams from the first and second conduits 12, 14 recombine. When the second removable section 36b is mounted on the monolithic section 36a of the housing 36, the second removable section 36b covers the blind bore 46. When the second removable section 36b is removed, the converging-diverging component 18 can be removed from the blind bore 46. This allows the convergingdiverging component 18 to be serviced or exchanged for another convergingdiverging component of a different size.

[0063] Figure 3 shows a more detailed cross-sectional view of the converging-diverging component 18 and the variable flow restrictor 20 of the fluid control system 10 of Figure 1. Other components of the pressure regulating system 2 have been omitted for clarity. The converging-diverging component 18 comprises a casing 19 that is a monolithic component machined from a single block of brass.

[0064] The casing 19 of the converging-diverging component 18 defines a converging nozzle 48 that receives fluid at the upstream pressure from the inlet conduit 6 via the filter 42. The cross-sectional area of the converging nozzle 48 decreases in the downstream direction (from right to left in Figure 3) to a minimum at the throat 50 of the converging-diverging component 18. The diameter of the throat 50 is approximately 1.7 mm, and the length of the throat is 1 mm. The length of the converging nozzle 48 is 6 mm. As the cross-sectional area of the nozzle 48 decreases, the velocity of the fluid flowing through the converging nozzle 48 increases, which causes the pressure of the fluid to decrease to the intermediate pressure p3.

[0065] The casing 19 of the converging-diverging component 18 defines a diverging nozzle 54 that extends in the downstream direction from the throat 50. The cross-sectional area of the diverging nozzle 54 increases in the downstream direction. As the cross-sectional area of the diverging nozzle 54 increases, the velocity of the fluid flowing through the diverging nozzle 54 decreases, which causes the pressure of the fluid to increase to the outlet pressure p2. The length of the diverging nozzle 54 is 25 mm.

[0066] The casing 19 of the converging-diverging component 18 further defines a plurality of control fluid taps 56 (one of which is shown in Figure 3) that extend radially outwards from the diverging nozzle 54 . The control fluid taps 56 extend from a point of the diverging nozzle 54 that is immediately downstream of the throat 50 of the converging-diverging component 18. The control fluid taps 56 connect the diverging nozzle 54 of the converging-diverging component 18 and the control fluid conduit 22, and therefore provide fluid at the intermediate pressure p3to the control fluid conduit 22. The total combined cross-sectional area of the taps 56 is greater than or equal to the cross-sectional area of the throat 50 of the convergingdiverging component 18. The variable flow restrictor 20 is rotatably arranged within a first through-bore 58 defined in the monolithic section 36a of the housing 36. The first through-bore 58 is perpendicular to the blind bore 46 and intersects and passes perpendicularly through the second conduit 14. Thus, fluid flowing through the second conduit 14 enters the first through-bore 58 through a first aperture, embodying a restrictor inlet 14a, in the second conduit 14 and leaves the first through-bore 58 through a second aperture, embodying a restrictor outlet 14b, in the second conduit 14.

[0067] Figure 4 shows a cross-sectional view of the variable flow restrictor 20, in a plane perpendicular to the plane of the cross-section shown in Figure 3 and parallel to the second conduit 14. The variable flow restrictor 20 is substantially cylindrical and comprises an adjustment knob 60, arranged on a proximal end of the variable flow restrictor 20 such that it protrudes out of the first through-bore 58 of the monolithic section 36a of the housing 36, and a restriction feature 62 arranged between the restrictor inlet 14a and the restrictor outlet 14b of the second conduit 14.

[0068] A circumferentially extending groove 64 is defined on the surface of the variable flow restrictor 20, adjacent, and on the proximal side of, the restriction feature 62. Along the length of the variable flow restrictor 20, the diameter of the variable flow restrictor 20 is less than the corresponding diameter of the first through-bore 58. Therefore, a gap embodying a restriction aperture 70 is defined between the outer surface of the variable flow restrictor 20 and the wall of the first through-bore 58. The restriction aperture 70 provides a fluid flow path between the restrictor inlet 14a, the circumferentially extending groove 64, and the restrictor outlet 14b.

[0069] The variable flow restrictor 20 extends beyond the full depth of the first through- bore 58, so that the distal end 66 of the variable flow restrictor 20 protrudes from the monolithic section 36a of the housing 36.

[0070] A first O-ring 72 is arranged on the proximal side of the circumferentially extending groove 64 and a second O-ring 74 is arranged on the distal side of the restriction feature 62. Thus, the first and second O-rings 72, 74 together seal the flow path between the restrictor inlet 14a and the restrictor outlet 14b so that fluid flowing along this flow path does not leak out of the monolithic section 36a of the housing 36. The second O-ring 74 is held in position by an annular bracket 76 that extends around the circumference of the variable flow restrictor 20 on the distal side of the second O-ring 74. The annular bracket 76 is arranged to abut both the second O- ring 74 and the monolithic section 36a of the housing 36.

[0071] The variable flow restrictor 20 further comprises a circlip 78 that extends around the circumference of the variable flow restrictor 20 on the distal side of the bracket 76. The circlip 78 acts as a stop to prevent movement of the variable flow restrictor 20 along its longitudinal axis in the proximal direction by abutting the bracket 76, which in turn abuts the monolithic section 36a of the housing 36. The bracket 76 and the circlip 78 are removably attachable to the variable flow restrictor 20, and can be attached to the variable flow restrictor 20 after the variable flow restrictor 20 has been inserted through the first through-bore 58 from the proximal side.

[0072] Fluid flowing through the second conduit 14 is turned through a right angle to follow the length of the variable flow restrictor 20 until the flow reaches the circumferentially extending groove 64. Having passed along the groove 64, the fluid then returns along the length of the variable flow restrictor 20 (in the opposite direction) before flowing through the restrictor outlet 14b.

[0073] As shown in Figure 3, the restriction feature 62 has a cross-section comprising a first spiral portion 62a and a second spiral portion 62b, diametrically opposed and each extending radially from a central point (i.e. thus resembling a tilde). The spiral portions 62a, 62b extend longitudinally along the variable flow restrictor 20 from the distal end of the restriction feature 62 to the proximal end of the restriction feature 62, adjacent the circumferentially extending groove 64.

[0074] It will be appreciated that rotation of the variable flow restrictor 20 (by rotating the adjustment knob 60) about the central longitudinal axis of the variable flow restrictor 20 causes the spiral portions 62a, 62b to move relative to the restrictor inlet 14a and the restrictor outlet 14b. Owing to the geometry of the restriction feature 62, the variable flow restrictor 20 is axi-asymmetric about its axis of rotation. This means that the cross-sectional area of the flow path from the restrictor inlet 14a to the restrictor outlet 14b in a plane parallel to the axis of rotation of the variable flow restrictor 20 (i.e. its central longitudinal axis) varies as the variable flow restrictor 20 is rotated. In the configuration shown in Figure 2, the variable flow restrictor 20 is arranged such that the first spiral portion 62a and the second spiral portion 62b are away from the restrictor inlet 14a and the restrictor outlet 14b, meaning that fluid can flow from the restrictor inlet 14a to the restrictor outlet 14b relatively easily. However, if the variable flow restrictor 20 is rotated (e.g. by 90 degrees) about its longitudinal axis (by rotating the adjustment knob 60), the spiral portions 62a, 62b are moved towards the restrictor inlet 14a and the restrictor outlet 14b, thereby restricting the distance between the outer perimeter of the restriction feature 62 (i.e. the tips of the spiral portions 62a, 62b) and the restrictor inlet and outlet 14a, 14b. As a result, the cross-sectional area of the flow paths connecting the restrictor inlet and outlet14a, 14b are reduced, meaning that the flow rate of fluid passing through the second conduit 14, around the variable flow restrictor 20, is reduced.

[0075] It will be appreciated that the extent to which the restrictor inlet 14a and the restrictor outlet 14b are closed by the spiral portions 62a, 62b of the restriction feature 62 may be adjusted by varying the rotation of the variable flow restrictor 20, thus controlling the flow rate of fluid through the second conduit 14. Rotating the adjustment knob 60 in the counter-clockwise direction results in a gradual increase in the radial distance between the perimeter of the restriction feature 62 and the restrictor inlet and outlet 14a, 14b. This means that the flow rate can be adjusted gradually between a minimum and a maximum flow rate.

[0076] As can be seen in Figure 2, the flow control system 10 comprises a control-fluid variable flow restrictor 26 within the control fluid conduit 22. The control-fluid variable flow restrictor 26 is structurally the same as the variable flow restrictor 20 in the second conduit 14, and is arranged in a second through-bore 68 that extends from an exterior surface of the housing 36 and intersects the control fluid conduit 22. The control-fluid variable flow restrictor 26 can be rotated within the second through-bore 68 so as to adjust the flow rate through the control fluid conduit 22, in the same manner as described above with reference to the variable flow restrictor 20 in the second conduit 14.

[0077] The pressure of the fluid flowing through the control-fluid variable flow restrictor 26 decreases from the intermediate pressure p3to the control pressure p4as it flows through the restriction of the control-fluid variable flow restrictor 26. The action of the control-fluid variable flow restrictor 26 is to limit the flow rate into and out of the control volume 34 to thus regulate the change in pressure p4in the control volume 34, so that the rate of the valve member 28 opening and closing may be controlled.

[0078] With the control-fluid variable flow restrictor 26 in its least restrictive configuration, the flow rate of the fluid into the control volume 34 is at its highest. Thus, this configuration corresponds to the fastest speed at which the pressure p4in the control volume 34 will balance with the upstream pressure p±, i.e. the fastest speed at which the valve member 28 will respond to a change in upstream pressure p±. It will be appreciated that this is the least damped configuration.

[0079] As the control-fluid variable flow restrictor 26 is rotated from this least restrictive configuration to its most restrictive configuration, the flow rate of the fluid into the control volume 34 is at its lowest. Thus, this configuration corresponds to the slowest speed at which the pressure p4in the control volume 34 will balance with the upstream pressure p±, i.e. the slowest speed at which the valve member 28 will respond to a change in upstream pressure p±. It will be appreciated that this is the most damped configuration.

[0080] Operation of the pressure regulating system 2 in pressure regulating mode (i.e. in which the downstream pressure is being controlled) will now be described, with reference to Figures 1 to 4.

[0081] The pilot valve 24 is configured to open and close according to the difference between a setpoint (e.g. provided by a loading spring acting on a diaphragm) and a sensed pressure, in this case the downstream pressure pout(e.g. acting on the underside of the pilot valve diaphragm).

[0082] When the downstream pressure poutis less than the setpoint, the pilot valve 24 opens. When the downstream pressure poutis greater than the setpoint, the pilot valve 24 closes.

[0083] In the closed configuration (when the downstream pressure poutis greater than the setpoint), fluid cannot flow from the inlet conduit 6 to the outlet conduit 8 via the flow control system 10 and the pilot valve 24. As there is no flow of fluid through the converging-diverging component 18, the outlet pressure p2(provided to the pilot valve 24), the intermediate pressure p4, and the control pressure p4(provided to the control volume 34 of the pressure regulator valve 4) equalise to the upstream pressure p±, i.e. p±= p2= p3= p4. This means that there is no fluid pressure differential across the valve member 28 of the pressure regulating valve 4.

[0084] The pressure regulating valve 4 comprises a biasing member (not shown) that acts on the valve member 28 of the pressure regulating valve 4 to close the pressure regulating valve 4. As there is no fluid pressure differential across the valve member 28 to oppose the force of the biasing member, the pressure regulating valve 4 closes. This causes the downstream pressure poutto decrease.

[0085] If the downstream pressure poutdecreases to become less than the setpoint of the pilot valve 24, the pilot valve 24 opens so as to permit fluid to flow from the inlet conduit 6 to the outlet conduit 8 via the flow control system 10 and the pilot valve 24. As fluid flows through the converging nozzle 48 of the converging-diverging component 18, the pressure of the fluid decreases at the location of the control fluid taps 56. Thus, when fluid is flowing through the converging nozzle 48, p3< p±, which means that the control pressure p4< p±. Therefore, there is a fluid pressure differential across the valve member 28 of the pressure regulating valve 4 that acts to open the pressure regulating valve 4, against the force of the biasing member. This causes the downstream pressure poutto increase.

[0086] The intermediate pressure p3, to which the fluid pressure is reduced as it flows through the converging-diverging component 18, is set by the ratio of the operating flow capacity of the pilot valve 24 to the flow capacity of the flow control system 10, and the control pressure p4in the control volume 34 depends on the intermediate pressure p3.

[0087] For a given upstream pressure p±when the pilot valve 24 is fully open, increasing the flow capacity of the flow control system 10 reduces the maximum ratio of the flow capacity of the pilot valve 24 to the flow capacity of the flow control system 10. As a result, the intermediate pressure p3, and thus the control pressure p4, increases for a given upstream pressure p±. This means that increasing the flow capacity of the flow control system 10 relative to the flow capacity of the pilot valve 24 has the effect of reducing the pressure differential across the valve member 28 of the pressure regulating valve 4. As a result, the gain of the pressure regulating system 2 is reduced, thus making the pressure regulating valve 4 more stable (at the expense of accuracy).

[0088] Conversely, decreasing the flow capacity of the flow control system 10 increases the maximum ratio of the flow capacity of the pilot valve 24 to the flow capacity of the flow control system 10, which decreases the intermediate pressure p3, and thus the control pressure p4, for a given upstream pressure p±when the pilot valve 24 is fully open. This increases the pressure differential across the valve member 28, meaning that the gain of the pressure regulating system 2, and the accuracy of the pressure regulating valve 4, may be increased (at the expense of stability).

[0089] As discussed above, the variable flow restrictor 20 allows a cross-sectional area of a flow path through the second conduit 14 to be varied. This means that the variable flow restrictor 20 can be used to increase or reduce the flow rate through the second conduit 14. By providing a variable flow restrictor 20 in the flow control system 10 in parallel with the converging-diverging component 18, it is not necessary to attempt to vary the flow capacity through the converging-diverging component 18 in order to vary the flow capacity of the flow control system 10, which can be significantly complex.

[0090] The total flow rate mcthrough the flow control system 10 is equal to the sum of the flow rate mAthrough the converging-diverging component 18 and the flow rate mBthrough the variable flow restrictor 20. Thus, by varying the flow rate mBthrough the variable flow restrictor 20, the total flow rate mcthrough the flow control system 10 as a whole can be varied. This allows the gain of the pressure regulating system 2 to be adjusted relatively straightforwardly, without requiring any components to be replaced.

Claims

Claims1. A fluid control system for a pilot-operated pressure regulating valve, the fluid control system comprising: an inlet port for receiving fluid at an upstream pressure from an upstream side of the pressure regulating valve; an outlet port for connecting to an inlet of a pilot valve for operating the pressure regulating valve; a first conduit defining a first flow path connecting the inlet port and the outlet port; and a second conduit defining a second flow path connecting the inlet port and the outlet port, the second flow path comprising a restriction aperture, wherein the second conduit is arranged in parallel with the first conduit; wherein the first conduit comprises: a converging portion for reducing the pressure of fluid flowing through the converging portion from the upstream pressure to an intermediate pressure, wherein the cross-sectional area of the first flow path through the converging portion decreases in a downstream direction; and a diverging portion for increasing the pressure of fluid flowing through the diverging portion from the intermediate pressure to an outlet pressure, wherein the cross-sectional area of the first flow path through the diverging portion increases in the downstream direction; wherein the system further comprises: a control fluid port for connecting to a control volume of the pressure regulating valve, wherein the control fluid port is configured to receive fluid at the intermediate pressure from the first conduit; and a variable flow restrictor within the second conduit, wherein the variable flow restrictor is arranged to selectively vary a cross-sectional area of the restriction aperture of the second flow path.

2. The fluid control system as claimed in claim 1 , wherein the converging portion of the first conduit comprises a converging nozzle defining at least a portion of the reduction in the cross-sectional area.

3. The fluid control system as claimed in claim 1 or 2, wherein the diverging portion of the first conduit comprises a step-change increase in cross-sectional area.

4. The fluid control system as claimed in any one of the preceding claims, wherein the diverging portion of the first conduit comprises a diverging nozzle defining at least a portion of the increase in cross-sectional area.

5. The fluid control system as claimed in any one of the preceding claims, wherein the first conduit comprises a throat defined between the converging portion and the diverging portion, wherein the throat defines the narrowest cross-sectional area of the flow path through first conduit, and wherein the control fluid port is configured to receive fluid from the first conduit at or adjacent the throat.

6. The fluid control system as claimed in claim 5, wherein the diverging portion of the first conduit comprises a constant-area section downstream of the throat, wherein a cross-sectional area of the constant-area section is constant along the length of the constant-area section.

7. The fluid control system as claimed in claim 5 or 6, wherein the fluid control system comprises one or more pressure taps connecting the first conduit and the control fluid port, wherein the total cross-sectional area of the pressure taps is greater than or equal to the cross-sectional area of the throat.

8. The fluid control system as claimed in any one of the preceding claims, wherein the variable flow restrictor is rotatably arranged within the second conduit such that the flow path through the second conduit is defined between an outer surface of the variable flow restrictor and an inner wall of the conduit, and wherein the variable flow restrictor is axi-asym metric about its axis of rotation such that the cross-sectional area of the flow path through the restriction aperture in a plane parallel to the axis of rotation varies as the variable flow restrictor is rotated.

9. The fluid control system as claimed in any one of the preceding claims, further comprising a housing, wherein the housing defines the inlet port, the outlet port, the first conduit the second conduit, and the control fluid port.

10. The fluid control system as claimed in claim 9, wherein the housing comprises a removable insert defining at least the converging portion and the diverging portion of the first conduit.

11. The fluid control system as claimed in claim 10, wherein the removable insert is a monolithic component.

12. The fluid control system as claimed in any one of the preceding claims, wherein the fluid control system further comprises a housing and an actuator for adjusting the variable flow restrictor, wherein the actuator is provided on an exterior surface of the housing.

13. The fluid control system as claimed in any one of the preceding claims, wherein the fluid control system further comprises: a control fluid conduit fluidly connecting the first conduit to the control fluid port; and a control-fluid variable flow restrictor within the control fluid conduit for selectively varying the cross-sectional area of a flow path through the control fluid conduit.

14. The fluid control system as claimed in any one of the preceding claims, wherein the fluid control system further comprises a filter between the inlet port and the first and second conduits.

15. A pressure regulating system comprising: a pressure regulating valve comprising: a housing defining a valve aperture; and a valve member movably mounted on the housing and arranged to move reciprocally to selectively open and close the valve aperture, thereby controlling a flow of fluid through the valve aperture, wherein the housing and the valve member together define a control volume and wherein the valve member is acted on by a control pressure in the control volume to control the position of the valve member; a pilot valve for operating the pressure regulating valve; anda fluid control system; wherein the fluid control system comprises: an inlet port connected to an upstream side of the pressure regulating valve so as to receive fluid at an upstream pressure; an outlet port connected to an inlet of the pilot valve; a first conduit defining a first flow path connecting the inlet port and the outlet port; and a second conduit defining a second flow path connecting the inlet port and the outlet port, the second flow path comprising a restriction aperture, wherein the second conduit is arranged in parallel with the first conduit; wherein the first conduit comprises: a converging portion for reducing the pressure of fluid flowing through the converging portion from the upstream pressure to an intermediate pressure, wherein the cross-sectional area of the first flow path through the converging portion decreases in a downstream direction; a diverging portion for increasing the pressure of fluid flowing through the diverging portion from the intermediate pressure to an outlet pressure, wherein the cross-sectional area of the first flow path through the diverging portion increases in the downstream direction; wherein the fluid control system further comprises: a control fluid port connected to the control volume of the pressure regulating valve, wherein the control fluid port is configured to receive fluid at the intermediate pressure from the first conduit; and a variable flow restrictor within the second conduit, wherein the variable flow restrictor is arranged to selectively vary a cross-sectional area of the restriction aperture of the second flow path.

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