GB2505168A

GB2505168A - A fluid flow control device for a double-acting piston actuator

Info

Publication number: GB2505168A
Application number: GB1214252.7A
Authority: GB
Inventors: James Fishwick
Original assignee: BiFold Fluidpower Ltd
Current assignee: BiFold Fluidpower Ltd
Priority date: 2012-08-01
Filing date: 2012-08-09
Publication date: 2014-02-26
Anticipated expiration: 2032-08-09
Also published as: GB2505168B; GB201213665D0; GB201214252D0

Abstract

First 64 and second 66 supply valves selectively block fluid flow between an inlet 1 and first 2 and second 4 outlets. A first exhaust valve 63 selectively blocks fluid flow between a first outlet 2 and a first exhaust port 3. A second exhaust valve 65 selectively blocks fluid flow between a second outlet 4 and a second exhaust port 5. A reciprocating piston 35 and valve stem 36 in the housing 25 is engagable with each of the valves 63-66. The piston 35 is moveable in response to a difference in forces applied by the fluid pressure of the pilot signal and the fluid pressure at one of the exhaust ports 3,5. It is moveable between a first position in which all valves 63-66 are in the closed positions, a second position in which the first supply 64 and exhaust 63 valves are open and the second supply 66 and exhaust 65 valves are closed, and a third position in which the second supply 66 and exhaust 65 valves are open and the first supply 64 and exhaust 63 valves are closed. At least one biasing member biases the valves 63-66 to the closed position. At least one leak path is defined in each of the valves 63-66 so as to ensure equalisation of pressures across them.

Description

A FLUID FLOW CONTROL DEVICE

The present invention relates to a fluid flow control device and more particularly, but not exclusively, to such a device that is used to control the flow of pneumatic or hydraulic fluid to an actuator of the kind used to operate the position of a valve.

In many applications it is desirable to automate the actuation of a pipeline valve via a remote control system. This is particularly necessary in harsh environments such as, for example, a petrochemical pipeline located on land or off-shore. The operation of, for example, a ball valve in such a pipeline is often effected by a valve positioner that provides fluid (typically pneumatic) signals to an actuator for operating the valve. A compressor delivers compressed air via a filter regulator to the positioner which controls the onward flow to the actuator by reference to position feedback signals. The regulator is required to reduce the available pressure from the compressor to a safe working level for the downstream positioner and associated pneumatic circuit.

The actuator typically comprises a piston and cylinder arrangement with a shaft associated with the piston being connected to the valve being operated. The piston divides the cylinder into a pair of chambers at least one of which may be selectively pressurised by the introduction compressed air in order to move the piston and therefore the shaft. In a single-acting piston, the other chamber is occupied by a biasing member such as a spring against which the pressurised air acts. When the pressurised air supply drops below a certain value the force applied by it to one side of the piston is less than that applied on the other side by the spring in which case the pressurised air is exhausted from the cylinder. In a double-acting piston air is selectively supplied to one of the chambers and simultaneously exhausted from the other.

The positioner generates pneumatic control signals which are not, in some applications, of sufficient volumetric flow rate to operate the actuator in the desired time period. It is therefore often necessary to employ a volume booster to ensure there is a sufficient sustained volume of fluid available to the actuator to ensure a rapid response time. Volume boosters are generally controlled by a pneumatic pilot signal received from the positioner and ensure that the pressure and volumetric flow of the fluid delivered to the actuator is sustained to achieve the desired actuator stroke speed.

Separate flow regulators are often connected to the booster and this serves to increase the complexity of the system in terms of installation, servicing, maintenance and operation.

The pilot signals are generated by the positioner in response to a command signal directing the positioner to move the valve to a desired position. The command signal may be an open-loop signal or a closed-loop feedback electrical control signal that takes into account the position of the actuator. In an alternative arrangement the booster may be controlled directly by an electrical signal that operates a solenoid valve in the booster.

Our UK Patent No. GB 2459720 describes a three position volume booster for use with a single-acting piston. If a double-acting piston is used two such volume boosters are employed to work in parallel; one on each side of the piston. In such an arrangement it is necessary for the two boosters to be tuned accurately to one another in order to avoid one booster being activated before the other as this may result in an undesirable scenario such as, for example, both sides of a piston cylinder being connected to the air outlet port of both boosters at once.

It is an object of the present invention to obviate or mitigate the above, and other, disadvantages. It is also an object of one aspect of the present invention to provide for an improved, or alternative, fluid flow control device.

According to the present invention there is provided a fluid flow control device for controlling the flow of fluid to and from a double-acting piston actuator, the device comprising: a housing defining an inlet port, first and second outlet ports for connection to respective ports of the double-acting piston actuator, and first and second exhaust ports in fluid communication with the first and second outlet ports respectively; a pilot inlet port for receipt of a pilot signal; first and second fluid supply paths for supplying operating fluid to the double-acting piston actuator, the first fluid supply path extending between the inlet port and the first outlet port, the second fluid supply path extending between the inlet port and the second outlet port; first and second exhaust paths for exhausting operating fluid from the double-acting piston actuator, the first exhaust path extending between the first outlet port and at least one of the first and second exhaust ports, the second exhaust path extending between the second outlet pod and at least one of the first and second exhaust ports; a first supply valve in the first supply path for movement between open and closed positions so as to block selectively fluid flow along the path; a second supply valve in the second supply path for movement between open and closed positions so as to block selectively fluid flow along the path; a first exhaust valve in the first exhaust path for movement between open and closed positions so as to block selectively fluid flow along the path; a second exhaust valve in the second exhaust path for movement between open and closed positions so as to block selectively fluid flow along the path; a reciprocal actuating member in the housing and engageable with each of the supply and exhaust valves in order to move them between the open and closed positions, the reciprocal actuating member being moveable in response to a difference in forces applied by the fluid pressure of the pilot signal and the fluid pressure at one of the first and second outlet ports, between a first position in which the first and second supply valves and the first and second exhaust valves are in the closed positions, a second position in which the first supply valve and the first exhaust valve are open and the second supply valve and the second exhaust valve are closed, and a third position in which the second supply valve and the second exhaust valve are open and the first supply valve and the first exhaust valve are closed; at least one biasing member for biasing the valves to the closed position; and a leak path defined in each of the supply and exhaust valves so as to ensure equalisation of pressures across them.

Thus in the first position there is no flow. In the second position fluid may flow to the first outlet port and vented fluid flows from the second outlet port to one of the exhaust ports. In the third position fluid may flow to the second outlet port and vented fluid flows from the first outlet port to one of the exhaust ports. The fluid is preferably air but in certain applications may be another gas or even a liquid The fluid flow control device may be a volume booster. The double-acting piston actuator may preferably comprise first and second cylinders for pressurising opposite sides of a piston assembly. The first and second outlet ports of the fluid flow control device are, in use, in fluid communication with ports associated with the first and second cylinders. The fluid flow control device allows a first cylinder to be pressurised whilst at the same time allowing the second cylinder to be vented through an exhaust port.

The reciprocal actuating member may comprise a moveable member that may be disposed in the housing between a first variable volume chamber in fluid communication with the pilot inlet port and a second variable volume chamber in fluid communication with one of the first and second outlet ports. The moveable member is preferably movable in response to a differential force applied to it by the pressures in the first and second variable volume chambers. The moveable member may be a piston or a flexible diaphragm moveable relative to the housing.

There may be first and second moveable members disposed in the housing. A first moveable member may be disposed in the housing between a first variable volume chamber in fluid communication with the pilot inlet port and a second variable volume chamber in fluid communication with the first outlet port. A second moveable member may be disposed in the housing between a third variable volume chamber in fluid communication with the pilot inlet port and a fourth variable volume chamber in communication with the second outlet port. There may be first and second pilot inlet ports. The first and second moveable members may be disposed at opposite ends of the housing and may be connected to the same elongate valve stem.

There may be a bypass passage between one of the first and second exhaust ports and the second variable volume chamber. The passage may be defined in the housing or otherwise.

The reciprocal actuating member may be moveable in a first direction between the first position and the second position and in an opposite second direction between the first position and the third position. The first position may be between the second and third positions.

The first supply valve may comprise a moveable valve element and a valve seat against which the valve element is sealed in the closed position. The second supply valve may comprise a moveable valve element and a valve seat against which the valve element is sealed in the closed position. The first exhaust valve may comprise a moveable valve element and a valve seat against which the valve element is sealed in the closed position. The second exhaust valve may comprise a moveable valve element and a valve seat against which the valve element is sealed in the closed position.

The leak path may be defined in each of the moveable valve elements. The leak path has the effect of ensuring that the pressure is balanced across the valves when they are in the closed positions so that any force required to open the valves is not acting against a force imbalance across the valves.

The at least one biasing member may comprises a first biasing member for biasing the first exhaust valve to the closed position. The at least one biasing member may comprise a second biasing member for biasing the second exhaust valve to the closed position. The at least one biasing member may comprise a third biasing member for biasing the first supply valve to the closed position. The at least one biasing member may comprise a fourth biasing member for biasing the second supply valve to the closed position.

At least one of the biasing members may act between a fixed support member and the respective moveable valve element.

The biasing members may take any suitable form and in one embodiment are coil springs that are compressible between the fixed support member and the respective moveable valve element The reciprocating actuating member may further comprise an elongate stem for engagement with supply and exhaust valves. The elongate stem may be directly or indirectly coupled to the moveable member, such as, for example, a piston. The moveable member is preferably located towards one end of the housing. In the embodiment where there are first and second moveable members they are preferably connected to the same elongate stem and may be connected to opposite ends of the stem.

The elongate stem may be comprised of a plurality of stem portions that are connected together. At least two of the plurality of stem portions may be movable relative to one another so as to adjust the length of the elongate stem.

The first and second exhaust valves and the first and second supply valves may be disposed on the stem at spaced locations. They may be arranged such they are co-axial with the valve stem. In an embodiment where the length of the stem is adjustable the position of at least one of the exhaust and/or supply valve may be adjusted relative to the respective ports to ensure that the valves open or close the exhaust and/or supply paths effectively.

The elongate stem may have a plurality of projections for lifting the valve elements from respective valve seats against the force applied by the at least one biasing member.

The projections may take any suitable form but in one embodiment they are in the form of shoulders defined at a transition between differing diameter portions of the stem.

The shoulders may be annular.

The elongate valve stem may have first and second enlarged diameter portions that each define two shoulders. A first enlarged diameter portion has opposed shoulders, one for abutment with the first exhaust valve and an opposite shoulder for abutment with the second supply valve. The second enlarged diameter portion may have opposed shoulder, one for abutment with the second exhaust valve and the other for abutment with the first supply valve. The projections may be disposed on opposite on an opposite side of the valve to the respective biasing member.

At least one of the supply valves or the exhaust valves may comprise a poppet having a bore in which the elongate valve stem is received.

The, or each, biasing member may act between a fixed support member and a poppet At least one poppet may be received in a respective sleeve. A sealing ring for sealing against a respective valve seat may be fixed to an end of the sleeve and or to the poppet. It may be fixed or abutted against a flange of the poppet.

The sleeve may be supported in a bore of a respective fixed support member. The valve stem may pass through the bore.

There may be a bypass passage that provides fluid communication between at least one of the outlet ports and one of the variable volume chambers. The bypass passage may extend, at least in part, in a wall of the housing. It may be connected to an annular groove between two parts of the housing. The bypass passage may comprise a bore in one of the fixed support members. There may be first and second bypass passages, a first bypass passage providing fluid communication between the first outlet port and a variable volume chamber and the second bypass passage providing fluid communication between the second outlet port and a variable volume chamber.

There may be at least one bleed passage that provides fluid communication between the pilot port, at least one of the outlet ports and one of the variable volume chambers.

This bleed passage allows fluid to flow from the pilot port to a downstream outlet port in order to dampen the response of the reciprocal actuating member and therefore the response of the supply and exhaust valves. This serves to limit or prevent hunting of the fluid control device as the actuator approaches the desired position. A bleed valve may be in fluid communication with the pilot port and controls the bleed from the pilot port to the bypass passage and the variable volume chamber. The bleed valve may be disposed in a bleed port in the housing that is in fluid communication with atmosphere.

There may be two such bleed passages, one providing fluid communication between a first pilot port and a first outlet port and a second providing fluid communication between a second pilot port and a second outlet port.

According to a second aspect of the present invention there is provided a fluid flow control device as defined above and fluidly connected to a double-acting piston assembly, the first outlet port being connected to a first inlet port of the double acting piston assembly and the second port being connected to a second inlet port of the double acting piston assembly.

Specific embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic circuit diagram showing a double-acting piston actuator for operating a valve, the supply of air to the actuator being controlled by a volume booster that serves as a fluid flow device according to the present invention; Figure 2 is a longitudinal sectioned view of an embodiment of the volume booster of figure 1; and Figure 3 is a longitudinal sectioned view of a second embodiment of a volume booster that serves as a fluid flow control device according to the present invention.

Referring now to figure 1, there is shown a main valve 10 that, in use, would be fitted in a pipeline (not shown) for transporting fluid or gas. The valve is operable between open and closed positions by a pneumatically-operated actuator 12. In this exemplary embodiment the actuator 12 is a double-acting piston and cylinder assembly having two pistons 13a, 13b each of which is reciprocally disposed in a respective cylinder 14a, 14b. Between each piston 13 and cylinder 14 there is a transmission mechanism for translating movement of the pistons into appropriate movement of the valve 10.

The mechanism also ensures that the movement of the pistons is co-ordinated. The skilled person will be well aware of suitable mechanisms available in the art. One such example is a rack and pinion mechanism (not shown), with a respective rack associated with each piston arranged for translation and a pinion attached to rotary spindle 16 for rotating the valve (which may be, for example, a ball valve). The translation of the pistons 1 3a, 1 3b, and therefore the racks, is converted into rotation of the pinion and therefore the valve spindlel6 in order to move the valve between open and closed positions.

The valve is moved in one direction by the introduction of pressurised air into one of the cylinders 14a, 14b and allowing air to exhaust from the other cylinder 14a, 14b. For example, in figure 1 the valve lOis shown in a closed position with the first cylinder 14a (on the right-hand side in figure 1) pressurised with air such that the piston 13a has moved to the left. The other piston 13b has also moved to the left so as to exhaust air from the second cylinder 14b. In order to open the valve 10, the second cylinder 14b is pressurised with compressed air so that the piston 1 3b moves to the right. At the same time the other piston 1 3a will move to the right thus exhausting air from the first cylinder 14a.

Compressed air is selectively introduced into, or exhausted from, the cylinders 14a, 14b under control of a pilot-operated five port, three position volume booster 20. The introduction of compressed air to the circuit is depicted schematically at 21. It will be understood that this may be provided from a source such as a compressor or the like.

The pilot port P is connected to a pilot pressure line (not shown) in which the air pressure is determined by a valve positioner as described, for example, in our aforementioned UK Patent No. GB 2459720.

The five ports of the volume booster are labelled 1 to 5 in figure 1. An inlet port 1 is connected to the source of pressurised air 21. A first outlet port 2 is connected to the first cylinder that may be pressurised in order to effect closure of the valve. A second outlet port 4 is connected to second cylinder that may be pressurised in order to effect opening of the valve. Ports 3 and 5 are exhaust ports that allow air from the cylinders 14a, 14b to be exhausted through the volume booster 20. Each of the exhaust ports 3, may be fitted with breathers and/or flow control devices, if required.

As represented in figure 1, the volume booster 20 has three positions, each position representing a different mode of operation. In a first position, depicted in figure 1, a central section of the booster is aligned with the ports 1 to 5 such that flow between the five ports is blocked so that no air flows to or from the actuator 12 through the booster 20. In a second position the inlet port 1 is connected to outlet port 4 so that air is supplied to the second cylinder 14b so as to move the piston 13b to the right (as indicated by arrow A in figure 1) in order to effect opening of the valve. At the same time outlet port 2 is connected to exhaust port 3 so that air may be expelled from the first cylinder through the booster via outlet port 2 and exhaust port 3. In this position flow to the exhaust port 5 is blocked. In a third position inlet port 1 is connected to outlet port 2 so as to supply compressed air to the first cylinder in order to effect closure of the valve. At the same time outlet port 4 is connected to exhaust port 5 so as to permit air from the second cylinder to be exhausted through the booster. Flow to exhaust port 3 is blocked in this third position.

The booster has a bypass passage 22 with a bleed adjustment 23, the purpose of which will be described in relation to figure 2 A take off port 24 is optionally provided for connection to a pressure gauge for sensing the pressure in the second cylinder. A similar take off port (not shown) may be provided for sensing pressure in the first cylinder.

Referring now to figure 2, an exemplary volume booster is shown in detail in the first position (no flow between the five ports). It comprises a generally parallelepiped housing 25 with side and end walls 26, 27, 28, 29 that define an internal cavity 30 of substantially circular cross-section for receipt of a piston-operated valve assembly 31.

One side wall 26 of the housing 25 is penetrated by three of the pods: the inlet port 1 and the first and second exhaust ports 3, 5. The opposite side wall 27 is penetrated by the outlet ports 2, 4 and one of end walls 29 is penetrated by the pilot port P. In the particular embodiment depicted in figure 2, the housing 25 is defined by three principal components. A main body 32 defining the majority of the side walls, an end piece 33 that defines one end wall 29 and part of the side walls 26, 27 and an end plate 34 that defines the other end wall 28. It will be understood that the precise construction of the housing may take any suitable form.

The piston-operated valve assembly 31 comprises a plurality of valves 63-66 that are operated by a reciprocating actuating member in order to selectively open and close the outlet and exhaust ports 2-5. In this embodiment the actuating member is in the form of a piston 35 and an elongate valve stem 36 and is supported for reciprocal movement in the cavity 30 by three support members 37, 36, 39 that are each fixed relative to the housing 25. The piston 35 is fixed to one end of the valve stem 36 and is disposed in the end piece 33 adjacent to the end wall 29, where the cavity 30 is enlarged to define an enlarged cavity portion 30a. The piston 35 has an outer periphery that is substantially circular and slightly smaller than the diameter of the enlarged cavity portion 30a, but which is sealed to the inner surface of the cavity 30a by means of a suitable sealing ring 40 that is received in an annular groove. The piston 35 includes a disc-shaped plate 41 that retains the sealing ring 40 in an open groove of the piston 35 and prevents extrusion as the piston reciprocates in the housing 25. The valve stem 36 extends through the cavity 30 towards the opposite end wall 28.

A first support member 37 is disposed at the opposite end of the housing 25 from the piston, adjacent to the end wall 28. It has an internal blind bore 42 and provides a first spring seat 43 for a first coil spring 44 at one end of the piston-operated valve assembly, as will be described in more detail below.

A second support member 38 is disposed at the piston end of the cavity 30 and has an internal bore 45 through which the elongate valve stem 36 passes. The bore 45 penetrates an end wall of the second support member 38 to define an aperture 46 with a diameter that it is slightly greater than the diameter of the elongate stem 36.

Immediately adjacent to this narrow part of the bore, an 0-ring seal 47 is located around the stem 36 in an annular groove in the end wall. The elongate valve stem 36 is received in the aperture 46 and supported for reciprocal movement therein. A second spring seat 49 of the piston-operated valve assembly is located in the bore 45 around the valve stem 36 on the opposite side of the 0-ring seal 47 to the aperture 46 and serves to retain seal 47 in the groove in the end wall.

The second support member 38 serves to close the enlarged cavity portion 30a that is defined by the end piece 33 of the housing 25. The piston 35 serves to divide the volume of the enlarged cavity portion 30a into two variable volume chambers 50, 51. A first chamber 50 on one side of the piston 35 is pressurised by air from the pilot inlet port P and the second chamber 51 is pressurised by air from the second outlet port 4 (as will be described below). Thus the volume of each chamber is dependent on the position of the piston 35, which in turn is dictated by the respective pressures of the air in each variable volume chambers 50, 51.

The outer peripheries of the first and second support members 37, 38 are sealed to the interior surface of the housing 25 by means of suitable sealing rings.

A third support member 39 is disposed at a location approximately mid-way between the first and second support members 37, 38. It has a central bore 52 through which the valve stem 36 passes. An inwardly directed annulus 53 serves to reduce the bore diameter to a size that is slightly larger than the outer diameter of the elongate valve stem 36 and affords support for reciprocal movement of the stem, an 0-ring seal 54 being provided to prevent air leakage between the annulus 53 and the stem 36. A third spring seat 55 is located around the stem 36 and abuts the 0-ring seal 54 and annulus 53, thereby retaining seal 54 in an annular groove in the third support member 39.

The elongate valve stem 36 has two enlarged diameter portions 60, 61 spaced apart along its length and disposed such that they are approximately aligned with the first and second outlet ports 2, 3. Each enlarged diameter portion 60, 61 defines two annular shoulders 62a, b, c, d, one at each end of the portion, that interact with respective supply and exhaust valves. The first annular shoulder 62a of the first enlarged diameter portion 60 is defined towards a lower end of the stem 36 and abuts a first exhaust valve 63 disposed between first outlet port 2 and first exhaust port 3.

Similarly a first annular shoulder 62b of the second enlarged diameter portion 61 abuts a first supply valve 64 disposed between the inlet port 1 and the second outlet port 4.

The second annular shoulder 62c of the first enlarged diameter portion 60 abuts a second supply valve 66 disposed between the inlet port 1 and the first outlet port 2 and a second annular shoulder 62d of the second enlarged diameter portion 61 is defined towards an upper end of the stem 36 and abuts a second exhaust valve 65 disposed between second outlet port 4 and second exhaust port 5.

The four valves 63, 64, 65, 66 are each of the same general configuration. Each has a valve seat 67-70 that is defined by an annular valve seat member 71, 72. There are two such valve seat members, each defining two valve seats. A first valve seat member 71 is disposed radially inboard of the first outlet port 2, intermediate the first and third support members 37, 39 and a second valve seat member 72 disposed radially inboard of the second outlet pod 4, between the second and third support members 38, 39.

Each valve seat member 71, 72 is of cylindrical form with a radially outwards extending flange 73 at each end, a central bore 74 and a plurality of radially directed apertures 75 providing fluid communication between the central bore 74 and an annular volume 76 defined between the flanges 73. The first and second enlarged diameter portions of the valve stem 60, 61 are received within a respective central bore 74 with an annular clearance, and the annular volume 76 is aligned with a respective outlet port 2, 4.

The valves 63-66 each further comprises a poppet-style valve element with a cylindrical sleeve 78 and a flat-faced poppet 79 fixed thereto. Each sleeve 78 has generally cylindrical inner and outer surfaces, the latter being outwardly flared at one end where it terminates an annular end surface to which a valve sealing ring 80 is fixed. The valve sealing ring 80 is designed to seal against the respective annular valve seat 67-70. An inner surface of the sleeve 78, which is intended to receive the poppet 79, is radially stepped to provide an annular stop 81. The poppet 79 comprises a cylindrical body penetrated by a central bore 82 for receipt of the valve stem 36 and has a radially outward extending flange 83 that extends into abutment with the sealing ring 80.

The bore 82 in each poppet 79 has a diameter slightly larger than that of the stem 36 so as to allow relative movement of the poppet and stem. The poppet 79 is retained on the stem 36 between a respective annular shoulder 62a-d of the stem 36 and the annular stop 81 on the inside surface of the sleeve 78 and is biased against the shoulder 62a-d by virtue of a respective coil spring.

The poppet has a small bore tapping 84 that affords a leak path for the air so that the pressure acting on both sides of the valve is equal. As the surface areas on which the pressure acts are equivalent, this ensures that the fluid forces acting on each side of the poppet and sleeve combination are substantially balanced.

The valve seat members 71, 72 are sealed to the housing 25 by means of ring seals 85, one of which is disposed in an annular groove in the housing 25 adjacent to the outer periphery of each flange 73. It will be appreciated that, in an alternative embodiment, such seals may be located in annular grooves in the flanges rather than in the housing. In order to retain the relative positioning of the valve seat members 71, 72 relative to the support members 37-39, a plurality of spacers 86 are provided. Two sets of such spacers 86 are shown in the embodiment of figure 2, each set being aligned along an axis that extends substantially in parallel to the axis of the elongate stem 36.

The first exhaust valve 63 is located between the first support member 37 and the first valve seat member 71, towards the end plate 34 of the housing. The cylindrical sleeve 78 is received in the bore 42 defined by the first support member 37 and is sealed to the inside surface of the support member by means of an 0-ring seal 87 disposed in an annular groove in its outer surface. A first coil spring 44 is disposed around the valve stem axis and acts between the first spring seat 43 and the poppet 79 so as to bias the sealing ring 80 against the first valve seat 67 defined by the first valve seat member.

The first exhaust valve 63 is thus biased to a closed position so as to block the flow of air between the first outlet port 2 and the first exhaust port 3.

The second exhaust valve 65 is located towards the opposite end of the housing between the second support member 38 and the second valve seat member 72, towards the end wall 29 of the housing. The cylindrical sleeve 78 of the poppet valve assembly is received in the bore 45 defined by the second support member 38 and is sealed to the inside surface by means of an 0-ring seal 87 disposed in an annular groove in its outer surface. A second coil spring 88 is disposed around the valve stem 36 and acts between the second spring seat 49 and the poppet 79 so as to bias the sealing ring 80 against a first valve seat 68 of the second valve seat member 72. The second exhaust valve 65 is thus biased to a closed position so as to block the flow of air between the second outlet pod 4 and the second exhaust pod 5.

The first supply valve 64 is located between one end of the third support member 39 and the second valve seat member 72. The cylindrical sleeve 79 of the poppet valve assembly is received in the bore 52 defined by the third support member 39 and is sealed to the inside surface by means of an 0-ring 87 in the same manner as the other valves. A third coil spring 89 is disposed around the valve stem 36 and acts between the annulus 53 and the poppet 79 so as to bias the sealing ring 80 against the second valve seat 69 of the second valve seat member 72. The first supply valve 64 is thus biased to a closed position so as to block the flow of air between the inlet port 1 and the second outlet port 4.

The second supply valve 66 is located between the other end of the third support member 39 and the first valve seat member 71. The cylindrical sleeve 79 of the poppet valve assembly is received in the bore 52 defined by the third support member 39 and is sealed to the inside surface by an 0-ring 87 in the same manner as described above. A fourth coil spring 90 is disposed around the valve stem 36 and acts between the third spring seat 55 of the third support member 39 and the poppet 79 so as to bias the sealing ring 80 against a second valve seat 70 of the first valve seat member 71.

The second supply valve 66 is thus biased to a closed position so as to block flow of air between the inlet port 1 and the first outlet pod 2.

When the pressures in the first and second variable volume chambers are such that equal forces are applied on each side of the piston (in the embodiment shown this will generally be when the pressures are equal as the working area on each side of the piston is the same but it will be appreciated in alternative embodiments that other configurations are possible) the volume booster is in the first position, as shown in figures 1 and 2, in which the four valves 63-66 are closed.

When the pressure in the first variable volume chamber 50 (fed by the pressure in the pilot line through the pilot port P) is such that a force is applied to the piston 35 that is greater than that applied on the opposite side of the piston by the pressure in the second variable volume chamber 51, the piston 35 and valve stem 36 will be forced to the left (in the orientation shown in figure 2) against the biasing forces of the first and third springs 44, 89. As the valve stem 36 moves in this direction the annular shoulders 62a, 62b of enlarged portions 60, 61 of the valve stem 36 bear against respective poppets 79 and serve to move them and the corresponding cylindrical sleeves 78 to the left such that the sealing rings 80 are lifted off the respective valve seats 67, 69.

Thus the first supply valve 64 is opened so that air may flow along a path from the inlet port 1 to the second outlet port 4. In particular, it flows between the spacers 86 and the third support member 39, around the flared ends of the cylindrical sleeves 78 and between the sealing ring 80 and the valve seat 69 from where it egresses via the annular clearance between the valve stem 36 and the seat member 72 and then through the radial apertures 75. Similarly the first exhaust valve 63 is opened allowing air to flow along a path from the first outlet port 2 to the first exhaust port 3. In particular air flows into the annular clearance 77 between the first valve seat member 71 and the valve stem 36 via the radial apertures 75 then out between the sealing ring 80 and the valve seat 67, around the outside of the cylindrical sleeve 78 and around the spacers 86 to the exhaust port 3. This corresponds to the second position referred to in relation to figure 1 and air flows from the inlet pod 1 into the second cylinder 14b via outlet port 4 and out of the first cylinder 14a to exhaust port 3 via outlet pod 2, thus opening the valve 10.

The third position of the volume booster occurs when the pressure in the first variable volume chamber 50 falls below that in the opposite second variable volume chamber 51. The forces acting on the piston 35 move it and the valve stem 36 in the reverse direction (to the right in the orientation of figure 2) against the biasing forces of the second and fourth springs 88, 90. As the valve stem 36 moves in this direction the annular shoulders 62c and 62d of the enlarged portions 60, 61 of the valve stem 35 bear against the respective poppets 79 and serve to move them and the corresponding cylindrical sleeve 78 to the right such that the sealing rings 80 are lifted off the respective valve seats 68, 70. Thus the second supply valve 66 is opened so that air may flow along a path from the inlet port 1 to the first outlet port 2 in the same manner as described above in relation to the first supply valve. Similarly the second exhaust valve 65 is opened allowing air to flow from the second outlet port 4 to the second exhaust port 5 in the same manner as described above in relation to the first exhaust valve 63. This corresponds to the third position referred to in relation to figure 1 whereby air flows from the inlet port 1 into the first cylinder 14a via outlet port 2 and from the second cylinder 14b to exhaust ports via the outlet pod 4.

The sealing rings 80 of each of the valves 63-66 seal against the respective valve seats 67-70 at an effective sealing diameter with respect to the central axis of the booster (which coincides with that of the elongate valve stem 36). The 0-ring seals 87 provided in the outside surface of the sleeves 78 are designed to seal against the respective inner surfaces of the support members 37-39 at the same diameter as the effective sealing diameter. This ensures that no differential forces act on the valves 63- 66 when the same pressure acts on each end which might otherwise tend to open the valves.

The provision of the leak paths afforded by tappings 84 through poppet valves ensures that the valves are not loaded by the pressure of the fluid passing through the booster 20. Thus in order to effect reciprocal movement of the piston and valve stem to actuate the valves the force applied to it by the pressures in the variable volume chambers only has to be sufficient to overcome the spring forces (and negligible friction forces).

In the embodiment shown the second variable volume chamber 51 is in fluid communication with the second outlet port 4 by means of a bypass passage 91, a main portion of which extends in the side wall 27 of the housing and leads to an annular groove 92 between the main body 32 and the end piece 33. A small bore 93 in the second support member completes the bypass passage. Thus the mode of operation (and position) of the volume booster is dependent on the air pressure in the pilot line compared to that at the outlet port 4 (which corresponds to that in the second cylinder 1 4b of the valve actuator 12). In an alternative embodiment, the chamber 51 may be in fluid communication with the first cylinder 1 4a.

A bleed passage 95 in the end piece 33 that extends from a port 96 in the side wall 26 to the opposite side wall 27, via the pilot port P and then down to the small bore 93.

This provides a pilot feed pressure to the downstream second outlet port 4 (via bypass passage 91) and to the variable volume chamber 51 in order to dampen the response of the piston 35 and therefore the supply and exhaust valves 63-66. This serves to limit or prevent hunting of the fluid control device as the actuator 12 approaches the desired position. The bleed valve 23 (figure 1) is located in the port 96 and is used to control the bleed from the pilot port P to the bypass passage 91 and the chamber 51.

It will be evident to the skilled person that the piston 35 may be any suitable reciprocal actuating member. For example, it may be a flexible diaphragm, the degree of deflection being dependent on the pressure on opposite sides.

Figure 3 shows an alternative embodiment of the volume booster. The only difference between this embodiment and that of figure 2 is that the reciprocating actuating member of the piston operated valve assembly 31 has a second piston 135 disposed at the opposite end of the elongate valve stem 36 to the first piston 35. The actuating member is again supported for reciprocal movement in the cavity 30 by three support members 37, 38, 39 that are each fixed relative to the housing 25. In this embodiment the first support member 37 is identical in appearance to the second support member 38. The housing 25 is modified in that the end plate 28 is replaced with a second end piece 133 that is identical in configuration to the first end piece 33. Each piston 35, 135 is disposed in a respective end piece 33, 133 and is arranged for reciprocating movement in a respective enlarged cavity portion 30a.

Both the end pieces 33, 133 have a pilot port. The first end piece defines a first pilot port P1 and the second end piece defines a second pilot port P2. Thus the outermost variable volume chambers 50 and 150 are both selectively supplied with pilot pressure that acts on one side of each piston 35, 135. The variable volume chamber 151 on other side of the second piston 135 is in fluid communication with the outlet port 2 in the same manner as the variable volume chamber 51 (associated with the first piston 35) is in communication with the outlet port 4. In particular there is provided a second bypass passage 191 extending in the side wall 27 of the housing between the variable volume chamber 151 and the outlet port 2 and including to an annular groove 192 between the main body 32 and the end piece 133. A small bore 193 in the first support member 37 completes the bypass passage. There is also provided a second bleed passage 95 in the end piece 133 that extends from a port 196 in the side wall 26 to the opposite side wall 27, via the pilot port P2 and then down to the small bore 193.

When the pressure in pilot port Al is greater than that in the outlet port 4, the pressure in variable volume chamber 50 is greater than that in variable volume chamber 51 and therefore the resultant force tends to move the piston 35 in the direction right to left (in the orientation shown in figure 3), carrying with it the rest of the reciprocal actuating member. As described above this movement opens valves 63 and 64 so as to permit fluid flow from inlet port 1 to outlet port 4 (and therefore to the second cylinder 1 4b) and exhaust from first cylinder 14a to flow to exhaust port 3 via outlet port 2. Once the pressures in chambers 50 and 51 are such that the forces acting on each side of the piston 35 are equal, the flow stops as the valve moves to the first position.

When pressure in pilot port P2 is greater than that in the outlet port 2, the pressure in variable volume chamber 150 is greater than that in variable volume chamber 151 and the resultant force tends to move the second piston 35 from left to right so that valves and 66 are open thereby allowing flow from inlet port 1 to outlet port 2 (and to first cylinder 14a) and exhaust from the second cylinder 14b to flow to the exhaust port 5 via outlet port 4. Once the pressures in the chambers 150 and 151 reach a point where the forces acting on each side of the piston are equal, the flow stops.

A positioner (not shown) determines to which of the pilot ports P1 or P2 the pilot pressure is applied, depending on the sensed and desired positions of the actuator 12.

It will be appreciated that numerous modifications to the above described designs may be made without departing from the scope of the invention as defined in the appended claims. For example, the valve stem may be constructed of one or more pieces. In the embodiment shown in figure 2 it comprises two pieces that are coupled together by a screw thread at the enlarged diameter portion disposed within the first valve seat member 71. The two-part form facilitates assembly of the valve components on to the stem.

The described and illustrated embodiments are to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be protected. It should be understood that while the use of words such as "preferable", "preferably", preferred" or more preferred" in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and embodiments lacking such a feature may be contemplated as within the scope of the invention as defined in the appended claims. In relation to the claims, it is intended that when words such as "a," "an," "at least one," or "at least one portion" are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim. When the language at least a portion" and/or a portion" is used the item can include a portion and/or the entire item unless specifically stated to the contrary.

Claims

CLAIMSA fluid flow control device for controlling the flow of fluid to and from a double-acting piston actuator, the device comprising: a housing defining an inlet port, first and second outlet ports for connection to respective ports of the double-acting piston actuator, and first and second exhaust ports in fluid communication with the first and second outlet ports respectively; a pilot inlet port for receipt of a pilot signal; first and second fluid supply paths for supplying operating fluid to the double-acting piston actuator, the first fluid supply path extending between the inlet port and the first outlet port, the second fluid supply path extending between the inlet port and the second outlet port; first and second exhaust paths for exhausting operating fluid from the double-acting piston actuator, the first exhaust path extending between the first outlet port and at least one of the first and second exhaust ports, the second exhaust path extending between the second outlet port and at least one of the first and second exhaust ports a first supply valve in the first supply path for movement between open and closed positions so as to block selectively fluid flow along the path; a second supply valve in the second supply path for movement between open and closed positions so as to block selectively fluid flow along the path; a first exhaust valve in the first exhaust path for movement between open and closed positions so as to block selectively fluid flow along the path; a second exhaust valve in the second exhaust path for movement between open and closed positions so as to block selectively fluid flow along the path; a reciprocal actuating member in the housing and engageable with each of the supply and exhaust valves in order to move them between the open and closed positions, the reciprocal actuating member being moveable in response to a difference in forces applied by the fluid pressure of the pilot signal and the fluid pressure at one of the first and second outlet ports, between a first position in which the first and second supply valves and the first and second exhaust valves are in the closed positions, a second position in which the first supply valve and the first exhaust valve are open and the second supply valve and the second exhaust valve are closed, and a third position in which the second supply valve and the second exhaust valve are open and the first supply valve and the first exhaust valve are closed; at least one biasing member for biasing the valves to the closed position; and a leak path defined in each of the supply and exhaust valves so as to ensure equalisation of pressures across them.
2. A fluid flow control device according to claim 1, wherein the reciprocal actuating member comprises a moveable member that is disposed in the housing between a first variable volume chamber in fluid communication with the pilot inlet port and a second variable volume chamber in fluid communication with one of the first and second outlet ports, the moveable member being movable in response to a differential force applied to it by the pressures in the first and second variable volume chambers.
3. A fluid flow control device according to claim 2, wherein there are provided first and second pilot inlet ports and first and second moveable members, a first moveable member disposed in the housing between a first variable volume chamber in fluid communication with the first pilot inlet port and a second variable volume chamber in fluid communication with the first outlet port, a second moveable member disposed in the housing between a third variable volume chamber in fluid communication with a second pilot inlet port and a fourth variable volume chamber in fluid communication with the second outlet port.
4. A fluid flow control device according to claim 2 or 3, wherein there is provided a bypass passage between one of the first and second exhaust ports and the second variable volume chamber.
5. A fluid flow control device according to any preceding claim, wherein the reciprocal actuating member is moveable in a first direction between the first position and the second position and in an opposite second direction between the first position and the third position.
6. A fluid flow control device according to any preceding claim, wherein the first and second supply valves and the first and second exhaust valves each comprise a moving valve element and a valve seat against which the valve element is sealed in the closed position.
7. A fluid flow control device according to claim 6, wherein the leak path is defined in each of the moving valve elements.
8. A fluid flow control device according to claim 6 or 7, wherein the at least one biasing member comprises a first biasing member for biasing the first exhaust valve to the closed position and a third biasing member for biasing the first supply valve to the closed position.
9. A fluid flow control device according to claim 6, 7 or 8, wherein the at least one biasing member comprises a second biasing member for biasing the second exhaust valve to the closed position and a fourth biasing member for biasing the second supply valve to the closed position.
10. A fluid flow control device according to claim 8 or 9, wherein each biasing member acts between a fixed support member and the respective moving valve element.
11. A fluid flow control device according to any preceding claim, wherein the reciprocating actuating member comprises an elongate stem for engagement with supply and exhaust valves.
12. A fluid flow control device according to claim 11, wherein the elongate stem has a plurality of projections for lifting the valve elements from respective valve seats against the force applied by the at least one biasing member.
13. A fluid flow control device according to claim 12, wherein the projections are shoulders defined at a transition between differing diameter portions of the stem.
14. A fluid flow control device according to claim 11, 12 or 13, wherein the supply valves and the exhaust valves each comprise a poppet having a bore in which the stem is received.
15. A fluid flow control device according to claim 14, wherein each poppet is received in a respective sleeve, a sealing ring for sealing against a respective valve seat being fixed to an end of the sleeve.
16. A fluid flow control device according to claim 15, wherein each sleeve is supported in a bore of a fixed support member.
17. A fluid flow control device according to any preceding claim and fluidly connected to a double-acting piston assembly, the first outlet port being connected to a first inlet port of the double acting piston assembly and the second port being connected to a second inlet port of the double acting piston assembly.
18. A fluid flow control device according to any preceding claim, further comprising a bleed passage providing fluid communication between the pilot inlet port and one side of the reciprocal actuating member and to one of the first and second outlet ports.
19. A fluid flow control device according to any preceding claim, further comprising a bypass passage providing fluid communication between one side of the reciprocal actuating member and one of the first and second outlet ports.