GB2207528A - Fluid flow control with reduced noise - Google Patents

Abstract

Fluid flow control for high pressure fluid flow with reduced noise includes a valve with a control element 16 located between a valve chamber 11 and a valve outlet 13. The control element includes at least two cooperating co-axially directed tubular members 17-22 having transverse ribs 30,31 extending circumferentially about the walls of the tubular members. Fluid traverses a fluid path between the tubular members. The tubular members define a series of fluid paths which are selectively operable. The ribs may be differently shaped. Selected tubular members are relatively movable and can be related to each other in cup-nesting formation or in an oppositely directed relationship. The walls of the tubular members may taper. The valve poppet stem can taper and may be provided with ribs. The fluid path defined by this control element acts to be highly variable according to different flow conditions and substantially reduces valve noise. <IMAGE>

Description

FLUID FLOW CONTROL WITH REDUCED NOISE This invention relates to fluid flow control devices and methods for controlling fluid flow. In particular the invention is intended to provide a control for fluid flow under high pressure and with reduced noise. The need to reduce noise in control valves arises in industrial plants and equipment, particularly where noise from valves can be amplified by the environment. A quieter environment is desirable in confined spaces.

Fluid flow control valves having noise reducing mechanisms are well known. One manner of reducing noise is to provide a labyrinth path for the fluid flow in a valve. By forcing the fluid to traverse such a tortuous labyrinth path noise reduction is achieved. S U c h a path, however, is continuously in circuit and this can cause unnecessary friction and resistance to fluid flow when the path is not required for noise reduction.

Another manner of noise reduction is to provide the valve with successive chambers through which the fluid must pass, each chamber having a noise-reducing effect.

Yet another form of noise reduction is provided by multiple pathways in the valve. These systems are relatively cumbersome and not as efficient as possible in ensuring effective fluid flow at different pressures and flow requirements.

Another prior art method of effecting noise reduction is providing a series of discs, which have a flat face in which there are tortuous radial-like paths through which fluid must pass from the central portion of the disk towards the outer circumference. The discs are stacked and welded together. A problem which arises with the disc means relationship is that sediment becomes trapped in the tortuous pathways. The discs must then be discarded, and possibly the entire valve needs to be replaced.

Prior art noise reducing fluid control devices and systems, therefore, each have their limitations which the Applicants seeks to overcome with the present invention.

It is an object of the present invention to provide for fluid flow control by a device and method which the Applicants believe will provide the advantages of each of the known prior art systems, while substantially minimizing the disadvantages of each of these prior art systems.

SUMMARY By this invention there is provided a fluid control system which meets this objective.

A control device for controlling high pressure fluid flow with reduced noise includes a control element whereby a selected number of flow paths can be provided for the fluid flow, the paths providing labyrinth pathways as required by the pressure and flow conditions.

A fluid flow control device includes a body member having a chamber, an inlet to and an outlet from the chamber. A control element is located between the inlet and outlet and includes at least two cooperating coaxial tubular members. At least one of the walls of one of the tubular members includes rib formations extending at least partly circumferentially about the wall relatively transverse to the fluid flow between the chamber and outlet. A fluid flow path is formed between the walls of the tubular members such that fluid passing through the control element traverses the ribs.

A valve poppet is movable in the chamber to and from a valve seat to regulate fluid flow through the chamber.

Ribs may be provided, selectively, on inside and outside walls of the tubular members, and more than one tubular member may be provided. Means is provided to introduce selectively more than one fluid flow path into the active fluid flow path between the chamber and the outlet.

The tubular members may be located in a relatively nest-like location with the free ends directed in one direction. Alternatively, the tubular members are directed oppositely with the free ends facing each other.

The tubular members may also be relatively movable with each other. Throttling means can be provided on the poppet stem, and ribs can also be provided on the stem of the valve poppet.

In some form of the invention the throttle element is operable in a chamber relative the valve elements of a valve poppet and valve seat.

In some preferred forms the walls of the tubular members are tapered from a thicker base to thinner free ends.

The invention is further described with reference to the accompanying drawings.

DRAWINGS Figure 1 is a sectional elevation of a first embodiment of a fluid flow control device in accordance with the invention.

Figure 2 is a sectional elevation of a second embodiment of a control device in accordance with the invention.

Figure 3 is a sectional elevation of a third embodiment of a control device in accordance with the invention.

Figure 4 is a sectional elevation of a control device of a fourth embodiment of a control device in accordance of the invention.

Figure 5 is a partial sectional elevation of an alternative structure of elements of the control device.

Figure 6 is a view of the circular spacer elements in the embodiment of Figure 1.

DETAILED DESCRIPTION A fluid flow control device for controlling high pressure fluid flow with reduced noise comprises a body member 10 having a chamber 11, an inlet 12 to the chamber and an outlet 13 from the chamber. A valve poppet 14 is movable in the chamber 11 onto and from a valve seat 15 thereby to regulate fluid flow through the chamber. A control element 16 between the valve seat 15 and outlet 13 is provided to control fluid flow with reduced noise.

The control element 16 includes cooperating coaxial tubular members which in Figure 1 are illustrated with numerals 17, 18, 19, 20, 21, and 22. Tubular member 17 has the smallest diameter and progressively the tubular members 18, 19, 20, 21, and 22 have increasing diameters. The sizing of each diameter is such that there is provided between each of the respective tubular members 17 through 22, tubular fluid paths which, in Figure 1, are illustrated by numerals 23, 24, 25, 26, and 27 respectively.

The tubular members 17 through 22 have outside longitudinal walls. Only outside walls 28 and 29 are enumerated in the interest of simplicity. The outside walls 28 and 29 are provided with rib formations 30 and 31 respectively. The ribs 30 and 31 are shown at the base and free end portions of the tubular members 17 and 18. The phantom lines 32 and 33 indicate that the ribs 30 and 31 extend generally throughout the length of the walls of the tubular members 28 and 29. The rib formations 30 and 31 extend generally at least circumferentially around the tubular walls transversely relative to the direction of fluid flow the chamber 11 to outlet 13.

In Figure 1 the fluid flow in the spaces 23 through 27 would be substantially vertically downwardly towards the outlet 13. Fluid thus passes between the 28 and 29 walls of the tubular members and traverses a fluid path which is relatively tortuous and circuitous over the rib formations 30 and 31. In Figure 1 there is shown the series of co-axially arranged tubular members 17 through 22 which form a manifold of parallel different fluid paths. The tubular members 17 through 22 have a regular cylindrical structure.

The valve poppet 14 includes a piston 34 located towards the end of a stem 35 of the valve poppet 14. The piston 24 cooperates with a substantially cylindrical formation 36 which is constituted by the internal bore 236 of a series of circular elements 37, 38, 39 and 40 between which are sandwiched spacers 41, 42, 43, 44 and 45. This combination of circular elements 37 to 40 and spacers 41 to 45 provides the internal bore 236. The spacers 41 to 45 provide radially directed apertures in the bore 236 of the cylinder formation 36 through which fluid can pass. The spacer configuration 41 to 45 is such that radially outwardly directed pathways are formed between the circular elements 37 to 40 which respectively communicate with the fluid pathways 23 through 27 between the tubular members 17 through 22.

As the poppet 14 moves to and from its valve seat 15 the piston 34 moves upwardly and downwardly effectively within the bore 236 formed by cylinder wall formation 36. When the piston 34 is located across all the spacers 41 through 45 formed in the wall of cylinder 36, all the radial and longitudinal fluid paths through the control element are effectively closed. In the configuration illustrated in Figure 1 the valve seat 15 is sealed by the valve poppet 14 in the position shown.

Progressively, as the valve poppet 14 is lifted from the seat 15 the piston 34 moves upwardly in cylinder 36. By this action more of the radial pathways through spacers 41 through 45 become progressively opened so that progressively more of the fluid paths 23 through 27 are actively connected between the valve chamber 11 and the outlet 13. This provides for a variable multiple number of parallel pathways to be cumulatively added to the flow path. This is one manner for effectively reducing noise in the valve operation.

In the embodiment of Figure 1 each of the circular elements 37 through 40 with its respective cooperating tubular members 17 through 22 provides a cup-like member.

In that each of the tubular members 17 through 22 have increasing diameters which mate with the increasing diameters of the circular elements 37 through 40, the configuration is one of a substantially nesting series of spaced cup-like members.

The rib formations 30 and 31 are like circular rings which are formed about the outside wall of the tubular members 17 through 22. The number of ribs or rings 30 through 31 can differ for each of the tubular members 17 through 22 as required and similarly the spacing between the ribs 30 and 31 can vary according to prerequisite flow requirements. The ribs may have different shapes and may have longitudinal cuts located discreetly around the circumference thereby to regulate or control the fluid flow across the ribs as required.

In Figure 5 the ribs are illustrated with a different section, namely a tapered section 230 in wall 1231. The ribs 230 face square section ribbing 232 in the opposite wall 233. The advantage of such a tapered rib is to adjust flow conditions in a generally move gradual rather than step like manner. Also in Figure 5, the piston- 234 is shown with a base portion 235 relatively angled to the poppet stem 236. The effect of this is also to ensure gradual opening of the pathways 237 to 238 as the piston moves upwardly. By such action the fluid flow is more gradually and taperedly changed, rather than with the step wise changes in the embodiment of Figure 1 as each pathway opens.

The spacers 41 through 45 can be formed between two spaced rings of different diameters, namely an inner ring 400 and an outer ring 401. Radial spokes 402 extend between the inner ring and the outer ring, and the rings and spoke construction is such that there are radial pathways 403 formed in the spacers.

An alternative structure to the circular elements 37 through 40 and spacers 41 through 45 is that of a cylindrical manifold block with an internal bore and with holes longitudinally and radially formed to intersect effectively to form a distribution manifold.

An effect of the progressively increasing diameters of the tubular members 17 to 22 is that the area of flow for fluid passing from the chamber 11 towards the outlet 13 increases with the increasing diameter of the circular flow path space between the increasing diameter of tubular members 17 t 22 of the control element. Since the flow area increases along the flow path 24 to 27 through the valve this also has an effect of reducing noise. By this construction different labyrinth paths are added cumulatively into fluid flow through the control element according to desired flow conditions.

The valve body 10 also includes a pressurebalancing element 46 which includes a chamber 47 wherein there is located a cylinder 48 effectively connected to the valve poppet free end opposite to the end having piston 34. The opposite end of the valve poppet 14 includes a piston 49 which rides in cylinder 150, and a further balancing piston 50 riding within the cylinder wall 51 of chamber 47. The chamber 47 is fed through an aperture 52 to a pilot which enters the chamber 47 to one side of the piston 48. There is a second connection 53 to atmosphere which enters the chamber 47 on the opposite side of the piston 50. Activation through pilot aperture 52 causes the piston 48 to move in the chamber 47 appropriately and this causes the valve poppet 14 to move to or from the valve seat 15.This activates the valve whereby fluid can enter through the inlet 12 and the valve operates in the manner described.

Remotely from the cylinder 34 at the end of the valve poppet 14 there is an additional construction to assist in pressure balancing. This is constituted by a plug 54 which is threaded into a larger plug 55 which in turn is threaded to the valve body 10. A chamber 56 is provided between plugs 54 and 55 and a piston 57 remote from piston 34 on the valve poppet stem. Between the plug 54 and piston 57 there is located a helical spring 58. Two pressure balancing pathways are provided between the chamber 56, the first being a pathway 59 which connects chamber 56 with chamber 11. The second pathway 60 connects the space above piston 34 with atmosphere between the plug 55 and valve body 10. Nut 61 holds plug 55 in threaded location within the valve body 10. The spring 58 provides a biasing force acting on piston 57 and in turn regulates the movement of valve poppet 14.

The pressure balanced configuration constituted by the chamber 46 and assisted through the chamber 56 provides a valve configuration where the valve is relatively insensitive to inlet pressure variations.

In one example the operation of the fluid flow control valve or regulator of Figure 1 the inlet pressure is in a range of 4,000 to 4,500 PSI at a flow of 6,000 standard cubic feet per minute (SCFM). The outlet pressure is approximately 700 PSI at a flow rate of between 500 and 6,000 SCFM. The rib construction 30 and 31 controls the flow path expansion required and the noise generated by such a valve is markedly reduced and noise of prior art valves performing under the same inlet and outlet conditions.

The embodiment of Figure 2 illustrates a fluid flow control device wherein the tubular members 128, 129, 130 and 131 are differently configured and arranged relative to each other. The tubular members 128 and 130 are directed with their relative free ends 132 and 133 respectively opposite to the free ends 134 and 135 of the tubular members 129 and 131. Additionally, the walls of the tubular elements 129 and 130 are provided with internal rib formations 130 and external rib formations 301. In some embodiments, both the internal and external ribs can also be provided on members 128 and 131. The ribs 300 and 301 can have different sections and can even enter the. opposite spaces between the ribs 300 and 301.

With such a configuration the tubular members 128 to 131 can be constructed in two or more sectional components.

In Figure 2, the valve poppet 14 is also provided with throttling elements 136 and 137 respectively. The throttling elements 136 and 137 are cut-out slot formations 138 and 139 the stem of the valve poppet. The cut out formations interact with lips 140 and 141 inwardly directed from the tubular members 128. As the valve stem 14 moves relative to the valve seat the cutout formations 138 and 139 are located differently relative to the lips 140 and 141 such that a different degree of fluid can pass through the chamber 11 and into the control element for fluid flow control.

A pathway 59 for balancing pressure with the chamber 56 connects the chamber 56 through a space 142 to the outlet 13. This provides a feedback reaction which enhances valve control.

The valve structure of Figure 2 with the oppositely directed tubular members 128 through 131 provides a flow path which is balanced and permits for a valve which is relatively shorter than the valve in Figure 1. The piston 14 is relatively wider. The operation of such a valve is stable and the valve has reduced sensitivity to valve seat deformation and friction.

In the control device of Figure 3 there is included a throttling mechanism for the control device. The tubular members 201, 202, 203 and 204 are different to those of Figures 1 and 2 in that the inside wall of tubular wall 202 provides ribs 213. The outside wall of tubular member 202 is free of ribs. The outer tubular member 204 is rib-free. The relative location of the tubular members 202 and 204 are oppositely to the tubular members 201 and 203 in that the free ends 251 and 252 are directed oppositely and towards the ends 253 and 254.

The tubular member 204 is tapered having a base 205 which is relatively thicker than the free end 251 of the tubular member 204. The tubular members 202 and 204 are connected by a bridging element 207, and are together axially movable relative to the tubular members 201 and 203. Movement is guided by a circular shoulder 208 which is mounted in upstanding fashion on base member 209.

Bleed holes 210 and 211 are provided in the transverse wall 212 and bridging element 207 respectively. Bleed holes 210 and 211 are provided in elements 212 and 207 to equalize pressure as required.

The valve illustrated in Figure 3 has relatively fewer ribs 213 transversely arranged on the walls of the tubular members 201 to 204 and provides different flow characteristics. As fluid passes between two sets of opposing ribs 213 which are relatively aligned transversely, the flow in the narrow space between those ribs 213 is relatively higher than the flow in the larger space upstream or downstream of opposed ribs 213.

In the embodiment of Figure 4 the valve poppet is tapered longitudinally at 432 in the area of the stem 414 located in the valve chamber 411. Additionally, the tubular members 401, 402, 403 and 404 are longitudinally tapered between their respective base ends 405 and free ends 406 such that they are wider at the base ends 405 and narrower at the free ends 406.

The outside walls of each of the tubular members 401, 402, 403, and 404 are provided with ribs 430, and the facing walls of adjacent tubular members are relatively flat. The outside surface of valve poppet stem 414 is also provided with transverse ribs 431. The ribs 431 are located in the tapered area 432 of the valve stem 414 of valve poppet 14.

The configuration of valve of Figure 4 is that the free end 433 of the valve poppet stem 414 is anchored to a base plate 434 which mounts the tubular members 402 and 404. As the valve poppet stem 414 moves axially in the valve body, the tubular members 402 and 404 move axially away from or towards the oppositely located tubular members 401 and 403. In this manner the fluid flow control in the valve is effectively controlled.

The control device of Figure 4 is effective as a relatively lower flow control device due to the action of the tapering walls of the tubular members 401 through 404.

Although different embodiments of the invention have been described with reference to different illustrative examples, it should be readily understand that many different combinations of structure are possible within the spirit and scope of this invention.

The invention provides for variable, multiple pathways which are of a labyrinth nature, and which are arranged in successive stages or chambers in series configuration and parallel cumulative arrangement.

The arrangements illustrated in Figures 2 to 4 show a series type control system where progressively the pathway changes as the tubular member relationship relative to each other changes as the tubular formations adopt different relative axial formations. A longer path is created as the member separate, and thereby the fluid flow conditions are increasingly expanded between the inlet and outlet. With the invented system there is accordingly a noise reduction.

The control device can operate for gas and liquid fluid flow control as a valve or regulator for pressure and flow conditions as required. Although high pressures in the order of several thousand PSI can be controlled with the control device of the invention, it is anticipated that there will be important application even at much lower pressures in appropriate circumstances.

The features illustrated in the various embodiments of Figures 1 through 5 can be interchanged appropriately to provide the desired flow characteristics for the control device.

It should be understood that this invention is not limited to the details of construction and arrangements of components set forth in the description and illustrated in the drawings. The phraseology and terminology employed herein are for purposes of description and should not be regarded as limiting. For instance, although the tubular members are illustrated as cylindrical members they can have other non-cylindrical or non-circular configurations. The scope of the invention is set out and encompassed in the claims.

Claims (51)

1. A fluid flow control device for controlling fluid flow comprising a body member having a chamber, an inlet to and an outlet from the chamber, a valve poppet movable in the chamber onto and from a valve seat thereby to regulate fluid flow through the chamber to the outlet, a control element between the valve seat and outlet, the control element including at least two substantially coaxial members, at least one of the members being a tubular member and having ribs extending at least partly circumferentially about the member, the ribs being directed transversely to the fluid path from the chamber to the outlet, and the fluid path being formed between walls of the adjacent members whereby fluid passing between the members is adapted to traverse the ribs.

2. A control device as claimed in claim 1 wherein the tubular members include a series of co-axial tubular members thereby forming parallel fluid paths between respective adjacent tubular members.

3. A control device as claimed in Claim 2 including means for selectively locating one or more of the fluid paths formed between the tubular members in fluid connection between the chamber and outlet.

4. A control device as claimed in claim 3 wherein the selecting means is a piston affixed to the poppet, the piston cooperating with a cylinder wall, the cylinder wall providing apertures to the parallel fluid paths, and the apertures being located at different relative positions in the cylinder wall.

5. A control device as claimed in claim 4 wherein the cylinder is formed by a series of circular elements, the elements being spaced from each other by spacers in the cylinder wall, the elements having central bores adapted to be in alignment, and each element being sealingly connected with an end of a different tubular member, the elements having progressively different diameters such that the walls and circular elements form a substantially nesting series of spaced cup-like members with the spacers between the cup-like members.

6. A control device as claimed in any one of claims 1 to 5 wherein the ribs are provided about an outside wall of at least one of the tubular members.

7. A control device as claimed in any one of claims 1 to 5 wherein different tubular members have different numbers of ribs and the spacing of the ribs on each tubular member is different.

8. A control device as claimed in claim 1 wherein the tubular members selectively have differently shaped ribs.

9. A control device as claimed in any one of claims 1 to 5 wherein selected tubular members include ribs on inside and outside walls of the members.

10. A control device as claimed in claim 1 wherein selected tubular members interact from opposite directions, the tubular members being located relative to each other with their free ends oppositely directed thereby to form a series connected cumulative fluid path.

11. A control device as claimed in claim 1 wherein the ribs substantially encircle the tubular members and have a substantially square section.

12. A control device as claimed in claim 1 wherein the ribs substantially encircle the tubular members and at least some of the ribs have tapering sections.

13. A control device as claimed in claim 10 wherein the tubular members are axially movable relative to each other thereby to enhance fluid flow control.

14. A control device as claimed in claim 1 wherein the poppet stem is transversely ribbed.

15. A control device as claimed in anyone of claims 1 to 4 wherein selected tubular members include tapered walls, the tapered walls being relatively thinner at the free ends of the members than at the base of the walls.

16. A control device as claimed in any one of claims 1 to 4 wherein the stem of the valve poppet tapers over at least part of its length.

17. A control device as claimed in Claim 5 wherein the stem of the valve poppet tapers over at least part of its length.

18. A control element for a fluid flow control device for controlling fluid flow, the device including a body member having a chamber, an inlet to and an outlet from the chamber, a valve poppet movable in the chamber onto and from a valve seat thereby to regulate fluid flow through the chamber, the control element being adapted for location between the valve seat and outlet, the control element comprising at least two coaxial tubular members, at least one of the tubular members having ribs extending at least partly circumferentially about the member, the ribs being directed transversely to the fluid flow from the chamber to the outlet, and a fluid path being formed between the adjacent tubular members whereby fluid passing between the tubular members through the control element traverses the ribs.

19. A control element as claimed in claim 18 including a series of co-axially arranged tubular members thereby to form parallel fluid paths between respective adjacent tubular members.

20. A control element as claimed in claim 19 including means for selectively locating one or more of the parallel fluid paths formed between the tubular members in fluid connection between the chamber and outlet

21. A control element as claimed in claim 20 wherein the selecting means is a piston affixed to the poppet, the piston cooperating with a cylinder wall, the cylinder wall providing apertures to the parallel fluid paths, and the apertures being located at different relative positions in the cylinder wall.

22. A control element as claimed in claim 21 wherein the cylinder is formed by a series of co-axial circular elements, the circular elements being spaced from each other by spacers in the cylinder wall, the circular elements having central bores adapted to be in alignment, and each circular element being sealingly connected with an end of a tubular member, the circular elements having progressively different diameters such that the tubular members and circular elements form a substantially nesting series of spaced cup-like members.

23. A control element as claimed in anyone of claims 18 to 22 wherein the ribs are formed about an outside wall of the tubular members.

24. A control element as claimed in anyone of claims 18 to 22 wherein different tubular members have different numbers of ribs and the spacing of the ribs on each tubular member is different.

25. A control element as claimed in anyone of claims 18 to 22 wherein different tubular members selectively have differently shaped ribs.

26. A control element as claimed in anyone of claims 18 to 22 wherein selected tubular members include ribs on inside and outside walls of the tubular members.

27. A control element as claimed in any one of claims 18 to 21 wherein selected tubular members interact from opposite directions, the tubular members being located relative to each other with their free ends oppositely directed.

28. A control element as claimed in any one of claims 18 to 22 wherein the ribs extend circumferentially around the tubular members and the ribs have a substantially square section.

29. A control element as claimed in any one of claims 18 to 22 wherein the tubular members are axially movable relative to each other.

30. A control element as claimed in any one of claims 18 to 21 wherein selected tubular members include tapered walls, the tapered walls being relatively thinner at the free ends of the members than at the base of the walls.

31. A method of controlling fluid flow in a fluid flow control device having a body member with a chamber, an inlet to and an outlet from the chamber, a valve poppet movable in the chamber onto and from a valve seat thereby to regulate fluid flow through the chamber comprising passing fluid from the valve seat between at least two coaxial members, at least one of the members having ribs extending at least partly circumferentially about the member, the fluid passing transversely over the ribs when the fluid flows from the chamber to the outlet.

32. A method as claimed in claim 31 including passing the fluid through a series of co-axial parallel fluid paths between a series of respectively adjacent members, the members being tubular.

33. A method as claimed in claim 31 including passing the fluid through progressively an increasing fluid flow area as fluid traverses the control element.

34. A method as claimed in claim 33 wherein the fluid passes through a fluid path adapted to increase in series or fluid traverses the control element.

35. A method as claimed in anyone of claims 31 to 34 including moving the tubular members relatively ~axially thereby to enhance fluid flow control.

36. A control device as claimed in claim 1 including means for balancing pressure between the outlet and chamber.

37. A control device as claimed in claim 36 wherein the pressure balancing means includes a bleed line between the outlet and a chamber, the volume of the bleed line being regulated by an extension to the valve poppet.

38. A control device as claimed in claim 31 including means for balancing pressure at the valve inlet, said means include an extension to the valve poppet, the pressure at the inlet and atmospheric pressure and pressure from a pilot source regulating the relative location of the extension.

39. A control device as claimed in any one of claims 1 to 5 wherein selected tubular members are connected for cooperative movement.

40. A control device as claimed in any one of claims 1 to 5 wherein the fluid path from the chamber to the outlet traverses an increasing area of flow between the inlet and the outlet to the control element.

41. A control device as claimed in claim 4 including a distribution manifold for fluid from the chamber to the fluid path.

42. A control device as claimed in 41 wherein the distribution manifold includes a cylinder block having a series of apertures spaced at different locations for communication selectively with different paths of the parallel fluid paths.

43. A control device as claimed in claim 4 wherein the piston includes a tapered base whereby a face for cooperating relationship with the cylinder wall permits for a gradual cooperative interaction as the piston moves relatively on the cylinder.

44. A fluid flow control device for controlling fluid flow comprising a body member having a chamber, an inlet to and an outlet from the chamber, a control element between the inlet and outlet valve, the control element including at least two substantially coaxial members, at least one of the members being a tubular member and having ribs extending at least partly circumferentially about the member, the ribs being directed transversely to the fluid path from the chamber to the outlet, and the fluid path being formed between walls of the adjacent members whereby fluid passing between the members is adapted to traverse the ribs.

45. A control device as claimed in claim 44 wherein the tubular members include a series of co-axial tubular members thereby forming parallel fluid paths between respective adjacent tubular members.

46. A control device as claimed in Claim 45 including means for selectively locating one or more of the fluid paths formed between the tubular members in fluid connection between the chamber and outlet.

47. A control element for a fluid flow control device for controlling fluid flow, the device including a body member having a chamber, an inlet to and an outlet from the chamber, the control element being adapted for location, the control element comprising at least two coaxial tubular members, at least one of the tubular members having ribs extending at least partly circumferentially about the member, the ribs being directed transversely to the fluid flow from the chamber to the outlet, and a fluid path being formed between the adjacent tubular members whereby fluid passing between the tubular members through the control element is adapted to traverse the ribs.

48. A method of controlling fluid flow in a fluid flow control device having a body member with a chamber, an inlet to and an outlet from the chamber, comprising passing fluid from the inlet between at least two coaxial members, at least one of the members having ribs extending at least partly circumferentially about the member, the fluid passing transversely over the ribs when the fluid flows from the chamber to the outlet.

49. A method as claimed in claim 31 including passing the fluid through a series of co-axial parallel fluid paths between a series of respectively adjacent members, the members being tubular.

50. A control device substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

51. A method of controlling fluid flow substantially as hereinbefore described.

PATENTS ACT 1977 SPECIFICATION NO 2207528A The following corrections were allowed under Section 117 on 13 January 1989 Front page Heading (71) Applicant delete whole lines insert Air Dry Corporation (Incorporated in USA - California) 19338 Londelius Street Northridge California 91324 United States of America THE PATENT OFFICE 15 March 1989