AU675103B2 - Pressurised fluid flow control valve - Google Patents

Description

AUSTRALIA

Patent Act COMPLETE SPECIFICATI ON

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: ;r e r r r Priority: Related Art: Names(s) of Applicant(s): MODERN DRIVE ENGINEERING PTY. LTD. and PETER GRAEME ANTONY WENN Actual Inventor(s): Peter Graeme Antony Wenn Our Address for service is: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street MELBOURNE, Australia 3000 Complete Specification for the invention entitled: PRESSURIZED FLUID FLOW CONTROL VALVE The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 0804N 0804N PRESSURIZED FLUID FLOW CONTROL VALVE The present invention relates to a control valve and in particular to a fluid control valve for closing the fluid line in response to pressure loss. The control valve is applicable for use in hydraulic fluid lines of equipment where sudden or unexpected fluid pressure loss will cause injury to personnel or damage to equipment. It will be convenient to hereinafter disclose the invention in relation to that exemplary application, although it is to be appreciated that the invention is not limited to that application.

Elevated work platforms are used by many statutory authorities and private contractors for electrical transmission line maintenance and other work duties requiring temporary above-ground elevation of personnel and equipment. Those platforms are normally raised and lowered under action of pressurized hydraulic oil supplied to actuating rams or other drive motors through hydraulic circuit lines connected to a source of pressurized oil. Personnel on the platform often use hydraulic power tools such as saws, crimping tools and pruners, which are also powered by hydraulic oil supplied from the hydraulic circuit of the platform. In those circumstances, hydraulic lines extend up the platform from the pressurized oil 5 source to terminal couplings on the platform where the tools S can be connected into the circuit for operation.

A problem with this arrangement is that failure of the hydraulic circuit, through rupture or disconnection of a circuit line, causes loss of hydraulic fluid. That fluid loss may cause a malfunction in the platform or power tools being operated on the platform, leading to personnel injury or equipment damage. Moreover, given suitable conditions, oil spilled or sprayed from the circuit line may catch alight causing a fire. In any event, property damage, work delays and associated expense can result simply from the loss of oil.

In an effort to alleviate this problem and resultant effects, a hose burst check valve has been developed. The valve is installed in a hydraulic supply line at an upstream location and should oil flow along the line increase above a predetermined rate, the valve automatically closes. Thus, should a supply line burst or otherwise lose downstream integrity, so there is a sudden increase of oil flow through the valve, then the valve will respond by closing in order to limit oil loss at the burst site.

A disadvantage with this check valve is that it does not distinguish between flow rate fluctuations due to normal oil consumption and unexpected oil loss. Accordingly, the valve must be set to operate to close the line above a predetermined flow rate that could be experienced during normal line operation. As a result, if the line bursts, causing oil to leak at a flow rate below the predetermined flow rate, the valve will not operate to close the line.

An aim of the present invention is to provide an improved control valve for closing fluid flow lines in response to fluid loss.

According to a first aspect, the present invention provides a control valve for a fluid circuit having a supply line and a return line, the valve including a first passage arranged in use to be in communication with the supply line and a second assage arranged in use to be in communication with the return line and control means operable to compare the flow rates in the first and second passages, and wherein the control valve is responsive to the control means and operable to prevent fluid .0 flow in the supply line in response to a predetermined difference in the flow rates in the first and second passages.

In a second aspect, the present invention provides a control valve for a fluid circuit having a supply line and a return .55 line, the valve including a first passage arranged in use to be S in communication with the supply line, a second passage arranged in use to be in communication with the return line, and control means responsive to the rate of flow in the second passage to establish a valve closure flow rate, wherein when the flow rate in the first passage is greater than or equal to the valve closure flow rate, the control valve becomes operable to prevent the flow of fluid in the supply line.

Preferably, the control means is operable between a first and a second position wherein in the first position, the valve closure flow rate is at a minimum and in the second position the valve closure flow rate is at a maximum Preferably, the control means is operable between the first and second positions, such that the level of the valve closure flow rate established by the control means may be between the maximum and minimum rates.

Preferably the level of valve closure flow rate decreases as a result of a decrease in the rate of flow in the return line and the level of the valve closure flow rate increases as a result of an increase in the rate of flow in the return line.

Preferably, the control means includes a second passage pressure sensitive means responsive to a second passage pressure differential to locate the control means between the first and second position.

Preferably, the control valve includes a first drive means which is operable under fluid flow to create a pressure differential in the second passage.

Preferably the first drive means is connected in parallel to a section of the second passage and preferably the magnitude of the second passage pressure differential is dependent on the pressure drop across this section of the second passage.

:Preferably, movement of the control means between the first and second positions varies the resistance to flow in this section of the second passage.

S•In one embodiment of the present invention, the control valve further S 25 includes valve means which is operable to prevent fluid flow in the supply line.

S" Preferably the valve means comprises a closing device which is movable between an open position wherein fluid is able to flow in the supply line to a closed position wherein fluid is prevented from flowing in the supply line.

Preferably the closing device includes a first passage pressure sensitive means which is responsive to a predetermined first passage pressure differential to move from the open position to the closed position.

djh p57530A Preferably the first passage pressure differential is created over a section of the first passage and the magnitude of the first passage pressure differential created under a particular flow rate is dependent on the position of the control means.

Preferably the control valve includes a second drive means which is operable under fluid flow to create a pressure differential in the first passage. Preferably the second drive means is connected in parallel to a section of the first passage and preferably the magnitude of the first passage pressure differential is dependent on the pressure drop across this section of the first passage.

Preferably, the control means is able to vary the resistance to flow in this section of the first passage to thereby control the magnitude of the first passage pressure differential which is created under particular flow conditions.

As the closing device is operable to close in response to a predetermined first passage pressure differential, the flow rate required to establish this S 15 predetermined pressure differential is dependent on the control means. In this way the control means is able to establish the valve closure flow rate for the control valve.

In an alternative embodiment of the invention, the control means further includes a first passage pressure sensitive means which is dependent on the rate of flow in the first passage and wherein the control valve becomes operable to close when the difference in the size of the first passage pressure differential and the second passage differential is greater than a predetermined

S

level.

In a further aspect, the present invention provides a control valve for a fluid circuit having a supply line and a return line, the valve including a first passage arranged in use to be in communication with the supply line, a second passage arranged in use to be in communication with the return line, valve means operable in response to a predetermined pressure eifferential created by the fluid flow in the first passage to close the valve and control means responsive to fluid flow in the second passage and operable to vary the magnitude of the said pressure differential created by the flow in the first passage.

An advantage of the present invention is that the control valve is responsive to the flow rate in the return line to establish a valve closure flow rate which, when this flow rate occurs in the supply line, will cause the control valve to become operative to close. As this valve closure flow rate may vary depending on the rate of flow in the return line, the control valve is better able to distinguish between flow rate fluctuations due to normal oil consumption and unexpected oil loss. Furthermore, this distinguishing capability is further ge. enhanced by causing the valve to be responsive to a pressure 5 differential created by the flow rate in the return line.

A further advantage of a preferred embodiment of the present invention is that the control valve may be successfully used where transient pressure phases in the fluid circuit are experienced. The transient pressure phases may be due to the length or size of the hydraulic lines or due to the elastic properties of these lines.

To assist in further understanding of the invention, reference is now made to the accompanying drawings which illustrate three preferred embodiments of the present invention. It is to be appreciated that these embodiments are given by way of illustration only and that the invention is not limited by them.

In the drawings: Figure 1 Figure 2 Figure 3 Figure 4 is a schematic view of a hydraulic circuit incorporating a control valve according to a first embodiment of the invention, under conditions where the circuit is not in use; is the control valve of Figure 1 under normal operating conditions where the circuit is being used; is the control valve of Figure 1 when in a closed position; is a schematic view of the main section of a control valve according to a second embodiment of the present invention; is a schematic view of the secondary section of the control valve of Figure 4; is a schematic view of a control valve according to a second embodiment of the present invention when in an open position; and is the control valve of Figure 4 when in a closed position.

Figure 5 Figure 6 Figure 7 35 g 5 Figures 1 to 4 illustrat; a first embodiment of a control valve which is arranged to be connected to a hydraulic circuit 100. The circuit includes a supply line 101 which carries fluid from a supply source 102 to hydraulic machinery 103. A return line 104 completes the circuit by taking the fluid from the hydraulic machinery back into the supply source. A pump 105 is connected in the supply line to pressurize the fluid in the circuit and a valve 106 is incorporated as part of the hydraulic machinery.

The control valve 10 includes a housing 11 which is typically cast, fabricated or otherwise formed of metal. The housing incorporates a first passage 12 having inlet and outlet ports 13 and 14 respectively connected to the supply line 101 and a second passage 15 having inlet and outlet ports 16 and 17 respectively connected to the return line 104.

The control valve further includes a first chamber 18 and a second chamber 19. The chambers are cylindrical in shape and the first chamber is in communication with both the first and second passages and the second chamber is in communication with the first passage.

The first passage 12 includes a supply inlet passage 20, a primary flow passage 21 and a supply outlet passage 22. The supply inlet passage interconnects the supply inlet port 13 and the first chamber 18, the primary flow passage 21 interconnects the first chamber 18 with the second chamber 19 and the supply outlet passage interconnects the second chamber 19 and the supply outlet port 14.

The second passage includes a return flow passage 23 and a return outlet passage 24. The return flow passage 23 interconnects the return inlet port 16 and the first chamber 18 e and the return outlet passage 24 interconnects the first S chamber 18 and the return outlet port 17.

The first chamber 18 incorporates a pressure sensitive piston S 25 which is slidable within the chamber from a first position as illustrated in Figure 1 to a second position as illustrated in Figure 2. The piston is in the form of a spool having a .30 first member 26 which incorporates an outer face 27 and a S second member 28 which incorporates an outer face 29. The first and second members 26 and 28 are remote from each other and are interconnected by a bar 30. With this arrangement, the first chamber 18 is divided into three portions; a first 35 portion 31 in communication with the outer face 27 of the first member 26, a second portion 32 in communication with the outer face 29 of the second member 28, and a third portion 33, which is defined by the space between the first and second members 26 and 28 of the pressure sensitive piston 25. A biasing spring -8- 34 is located in the second portion 32 to bias the pressure sensitive piston 25 into the first position as illustrated in Figure 1.

The second chamber 19 also incorporates a pressure sensitive piston 35 which is also in the shape of a spool. The piston incorporates a first member 36 which has an outer face 37 and a second member 38 which incorporates an outer face 39. The members 36 and 38 are remote from each other and are interconnected by a bar 40. Similar to the first chamber, the piston 35 is slidable within the second chamber 19 from a first position as illustrated in Figure 1 to a second postion as illustrated in Figure 2. Also, the second chamber 19 is divided into three portions by virtue of the piston 35. The first portion 41 of the second chamber is in communcation with the outer face 37 of the first member 36, the second portion 42 is in communication with the outer face 39 of the second member 38 and the third portion 43 is defined by the space between the first and second members 36 and 38 of the piston The first piston 25 is responsive to a first pressure differential between the first portion 31 of the first chamber 18 and the second portion 32 of the first chamber 18 to cause it to move between the first position and the second position.

5 As the first portion 31 is in communication with the return flow passage 23 via opening 44, the pressure in the first portion 31 is dependent on the pressure in the return flow passage 23. In relation to the pressure in the second portion 32, a first connecting passage 45 interconnects the return flow o:o outlet passage 24 and the second portion 32 of the chamber 18 to provide fluid pressure to the second portion 32. A damping orifice 45a is located in the connecting passage 45 to delay any changes in the pressurization of the second portion 32 by slowing the flow of fluid through the passage The control valve 10 includes a first drive passage 46 which is e. ~in parallel with a section of the second passage 15. In particular, the first drive passage 46 interconnects the return flow passage 23 and the return flow outlet passage 24, thereby bypassing the first chamber 18.

The first drive passage 46 incorporates a constriction 48 wiich creates resistance to fluid flow in the passage to thereby create a pressure differential across this passage under flow conditions.

The first chamber 18 incorporates an opening 56 which allows fluid flow from the return flow passage 23 to the return outlet passage 24. The piston 25 is movable from the first position wherein it blocks the opening 56 to the second position wherein it is remote from the opening 56. As the piston 25 is able to constrict the size of the opening 56, its position determines the resistance to fluid flow through this section of the second passage.

The first pressure differential which the piston 25 is responsive to is dependent on the pressure drop across the section of the second passage in which the first drive passage 46 is in parallel.

The magnitude of the pressure drop is determined by two main factors, firstly by the proportion of fluid flowing through the first drive passage as compared to the fluid flowing through 5 the opening 56, and secondly by the amount of resistance to flow through the opening 56. As the passages are in parallel, the first factor is dependent on the resistance to flow through the opening 56 as it is the comparative resistance in the two passages which determines the amount of flow through each passage.

In this way, the magnitude of this pressure drop under particular flow conditions is dependent on the resistance to fluid flow through the opening 56. This in turn is determined 45 by the position cf the piston 25 between the first and second Spositions.

In a similar arrangement to the first chamber 18, the pressure sensitive piston 35 in the second chamber 19 is responsive to a pressure differential between the first portion 41 and the second portion 42 of the second chamber 19 to enable it to move from the first position to the second position.

A secondary flow passage 49 is arranged to interconnect the third portion 33 of the first chamber 18 and the first portion 41 of the second chamber 19 to thereby provide fluid pressure to the first portion 41. As the third portion 33 of the piston is in communication with the supply inlet passage 20 the fluid pressure in the first portion 41 is dependent on the fluid pressure which is in the supply line. A damping orifice 49a is also located in the secondary flow passage 49 to delay any changes in pressurization of the first portion 41.

In relation to the fluid pressure in the second portion 42 of the second chamber, a connecting passage 50 is arranged to interconnect the supply outlet passage 22 and the second portion 42 of the second chamber 19. In this way the pressure in the second portion 42 is dependent on the fluid pressure within the supply outlet passage 22. As the supply outlet passage 22 is in communication with the primary flow passage 21 via the third portion 43 of the second chamber 19, the pressure in the second portion 42 is dependent on the pressure in the top of the primary flow passage 21 adjacent the opening 52 into the third position 43. A damping orifice 50a is located in the connecting passage 50 to delay any changes in pressurization of the second portion 42 by slowing the flow of fluid through the passage 30 A second drive passage 66 is arranged to interconnect the secondary flow passage 49 and the primary flow passage 21.

With this arrangement, the second drive passage creates a passage in parallel with a section of the first passage 12, thereby bypassing the lower section of the primary flow passage 21 and opening 54 interconnecting the primary flow passage 21 and the third portion 31 of the first chamber 18. The second drive passage 66 incorporates a constriction 53 which is arranged to create a pressure differential under fluid flow conditions within the passage 66.

-11- As the pressure in the second portion 42 is dependent on the fluid pressure at the top of the primary chamber 21 adjacent opening 52, the second pressure differential is dependent on the pressure drop across this section of the first passage 12 in which the second drive passage 66 is in parallel.

The second chamber 19 is in communication with the primary flow passage 21 through opening 52, the secondary flow passage 49 through opening 47 and to the supply outlet passage 22 through opening 17. The second piston 35 is arranged to act as a closing device to be operable to prevent fluid flow through the first passage by prevent.ng flow of the fluid from the primary flow passage into the second chamber 19. In particular, the piston is movable from the first or open position as illustrated in Figure 1 wherein the first member 36 is remote from the openings 52 and 57 thereby allowing fluid flow into the second chamber from both the primary and the secondary flow passages, to the second or closed position as illustrated in Figure 3 wherein the first member 36 is seated over the opening 52 to thereby prevent fluid flow from the primary flow chamber into the second chamber 19.

oeoo The first chamber 18 incorporates the openiig 54 which allows fluid flow from the third portion 33 into the lower part of the primary flow passage 21. The first piston 25 is movable from the first position wherein the second member 28 of the piston blocks the opening 54 to the second position wherein it is remote from the opening 54. As the piston 25 is able to constrict the size of the opening 54, it determines the resistance to flow of fluid through this section of the first passage. Similar to the earlier described pressure drop, under any particular flow conditions, the magnitude of the pressure drop across this section of the first passage in which the 35 second drive passage 66 is in parallel, is dependent on the .e resistance to flow through the opening 54 and this is determined by the position of the piston The second piston 35 is biased into the first position by -12- _1~ biaring spring 58. However, at a predetermined second pressure differential, a resultant force on the piston 35 is created which is greater than the biasing force of the spring 58. This force causes the piston to move frem the first position to the second position.

Consequently, the position of the first piston 25 determines the magnitude of the second pressure differential which is created under particular flow conditions. As the second piston 35 is operable to close in response to a predetermined second pressure differential, the flow rate required to establish this predetermined second pressure differential is dependent on the position of the first piston 25. In this way, the piston 25 is able to establish the level of the fluid flow rate through the first passage which will cause the second piston to move from the open position to the closed position.

The control valve 10 further incorporates a delay facility 59 which is operable to limit the fluid pressure in the first portion 41 of the second chamber 19 to thereby effect the pressure differential acting on the second piston 35. The delay facility provides a capacitance type effect to slow an increase in the fluid pressure in the first portion 41 as the amount of fluid flowing into the secondary flow passage increases.

In the illustrated arrangement, this delay facility 59 is in the form of pressure accumulators 60 and 61 which are in a suitable position to bleed fluid away to regulate the pressure in the first portion 41. As more thzn one accumulator is used, the capacitance effect is staggered such that a first accumulator operates over a first fluid pressure range and a second accumulator over a second fluid pressure range. The accumulators 60, 61 are connected via fluid passages 62 and 63 to the first portion 41 of the second chamber 19. One of the accumulators 60 is in the form of a spring accumulator which op es typically over a fluid pressure range of 0 bar to bar, whereas the other accumulator 61 is a gas accumulator which operates over the fluid pressure range of 35 bar to the -13full system pressure of 140 bar.

In operation of the valve under start up conditions as illustrated in Figure 1, the valve 106 of the hydraulic machinery 103 is closed, and the supply line 101 is pressurized under action of the pump 105. The first piston 25 is in the first position and the second piston 35 is in the open position. Under these conditions, fluid flows through the supply inlet port and into the third portion 33 of the first chamber 18. As the opening 54 is blocked fluid flows through the secondary flow passage 49 and flows both into the first portion 41 of the second chamber 19 and also through the second drive passage 66 into the primary flow passage 21. As the second piston 35 is open fluid flowing from the second drive passage 66 is able to flow through the primary flow passage into the third portion 43 of the second chamber 19 and through to the supply outlet passage 22 and continue in the supply line to the valve of the hydraulic machinery. Futhermore, fluid is able to flow through the connecting passage 50 and into the second portion 42.

The pressure in the first portion 41 does not build up initially as the fluid in the first portion bleeds away initially into the spring accumulator 60 and as pressure builds, into the gas accumulator 61. Consequently the second pressure differential is not initially created between the first portion 41 and the second portion 42 which would cause the piston 35 to move to the closed position.

M.0 Fluid continues to flow through the supply line to the valve 106 until the pressure reaches its operating pressure which would typically be 140 bar.

Under start up conditions, as the valve 106 is closed the pressure in the return line including the return flow passage 23 and the return flow outlet passage 24 is the same as the pressure in the supply source 102.

Once the valve 106 is opened and the hydraulic machinery is in -14use, fluid then flows through to the return line 104 and flows through the return flow passage 23 and the return flow outlet passage 24. As the first piston 25 is in the first position, the opening 56 is blocked and fluid in the return flow passage 23 is caused to flow through the drive passage 46 into the return flow outlet passage 24. Due to the constriction 48 in the first drive passage 46, a pressure differential is created between the return flow passage 23 and the return flow outlet passage 24. By virtue of the flow of fluid into the second portion 32 of the first chamber 18 through the connecting passage 45, this pressure drop is transferred to the second portion 32 thus creating a pressure differential between the first and second portions of the piston Initially, the size of this pressure differential between the return flow passage 23 and the return flow outlet passage 24 is dependent on the rate of flow of fluid through the drive passage 45 and is arranged such that under normal operating conditions the resultant force acting on the spool from this pressure differential is greater than the biasj. g force of the spring, and therefore the piston 25 is caused to move from the first position towards the second position.

Movement of the piston towards the second position opens openings 56 and thus allows fluid flow through the opening 56 to the return flow outlet passage 24. This creates a parallel flow with the first drive passage 46 and effects the pressure drop created in the return flow outlet passage. As the piston continues to move towards the second position, the opening 56 is less constricted by the piston 25 and a higher proportion of the fluid flow in the second passage will flow through the opening 56. This will cause the pressure differential to decrease until such time as the resultant force acting on the piston 25 equals the biasing force and the piston will stop moving. The exact position it will stop between the first and second position will depend on the strength of the spring, the rate of flow and the configuration of the passages and openings.

Once the piston 25 moves from the first position, the opening 54 begins to open and fluid is able to flow through from the first chamber 18 into the primary flow passage 21.

Once fluid is able to flow through opening 54 then a parallel flow is created through opening 54 and through the second drive passage 66. This parallel flow effects the pressure drop which is created in the top of the primary flow chamber 21 as the proportion of fluid flowing through the second drive passage 66 decreases. The exact proportion will depend on the size of the opening 54 which in turn is dependent on the position of the piston 25. With this parallel flow, the magnitude of the pressure drop created under any flow rate decreases and therefore the amount of flow required through the first passage 12 to create the second pressure differential to cause the second piston 35 to close increases. In this way the value of valve closure flow rate increases.

In this position, the control valve is under normal operating conditions, the valve closure flow rate is higher than the normal operating flow rates in the supply line, and the fluid flow is relatively unrestricted.

While the integrity of the circuit remains in tact, the control valve will maintain this configuration as long as the machinery is operated.

If the integrity of the circuit is broken, then the amount of fluid which returns through the fluid return line will decrease. Consequently the rate of fluid flow through the 0 first drive passage 45 will decrease thus causing the pressure differential acting on the first piston 25 to decrease. Once this flow rate decreases the forces acting on the piston will become unbalanced and the piston 25 will be caused to move with the biasing spring back towards the first position until a new equilibrium of forces is established on the piston 25 or if no equilibrium is reached, the piston will move back to the first position.

Once the piston moves back towards the first position, the -16opening 54 becomes more constricted and more flow is diverted to the second drive means 66. In this way, the magnitude of the second pressure differential which is created at a particular flow rate increases, therefore resulting in a decrease in the value of the valve closure flow rate.

As fluid will still continue to flow through the supply inlet passage 20, the magnitude of the second pressure differential created will increase. Furthermore, if the flow rate is above the newly established valve closure flow rate, the piston 35 is caused to move from the open position to the closed position.

Furthermore, as the first member 38 of the piston 35 moves over the opening R2 the size of the opening decreases thus increasing the pressure differential acting on the piston which further assists in movement of the second piston to close off the primary flow passage 21. Once the second piston has closed the opening 52, fluid flow through the first passage is prevented thereby blocking the flow of fluid through the supply line. This configuration is illustrated in Figure 3.

The control valve 10 further includes a reset facility to move the piston 35 back into the open position. This reset facility comprises a reset flow passage 64 which interconnects the secondary flow passage 49 and the second portion 42 of the second chamber 19. A valve 65 is operable to open and close this reset flow passage. On opening of this passage the pressure in the first portion 41 and the second portion 42 are equalised thus causing the piston to move to the open position under the force of the biasing spring.

The control valve also incorporates a test facility.

The test facility includes a test flow passage 67 which o. interconnects the supply outlet passage 22 and the return flow outlet passage 24. A valve 68 is operable to open and close the test flow passage 67. Once the test flow passage 67 is open fluid is diverted from the supply outlet passage 22 directly to the return flow outlet passage 24. This simulates a leak in the system which causes flow in the first passage 12 -17and decreases the rate of flow in the return flow passage 23 thus causing the control valve to become operable to close off the primary flow passage 21.

The reset and test facilities may be spring operated levers or the like so that they are only operable on being held down.

In practice, pressure differentials will occur throughout the circuit due to friction losses in the flow lines and in any machinery through which the fluid passes. An advantage of the control valve 10 is that these pressure differentials can be accommodated in the valve and will not cause the valve to inadvertently close.

A further advantage of the control valve is that it can be tailored to suit different flow circuits. In particular the size of the pressure differentials to cause actuation of the first or the second pistons can be varied merely by varying the characteristic of the springs. Furthermore, the performance 20 characteristic of the valve 10 is particularly influenced by e, the characteristics of the spring acting on the first piston 25, the softer the spring, the less sensitive to changes in e flow and the valve 10 will remain open for larger differences S. in flow. Furthermore, typically the bias spring force acting on the piston 35 is larger than the biasing spring force acting on the piston The delay facility 59 may be of any suitable form to regulate the pressure differential created on the second piston Furthermore the type and size of the accumulator would be selected as appropriate to the operating pressure range required and the volume and elastic properties of the fluids circuit.

Furthermore, the size of the pressure differentials which are created by the first and second drive means under flow conditions can be altered by using different configurations.

In particular the size of the passages, openings and constrictions all influence the size of any pressure -18differential which is created under a particular flow.

Furthermore, it is envisaged that the configuration of these drive passages may be adjustable thereby enabling the characteristics of the control valve to be further adjusted.

The amount of leakage at zero return flow which is required to operate the control valve to close is highly dependent on the characteristics of the circuit and would vary depending on the circuit size and use. However, it is envisaged that in many applications a leakage of approximately 500 cc/minute would be a typical rate whcih would cause closure of the second piston An important advantage of the control valve 10 is that with the arrangement of the first and second pistons 25 and 35, there is a delay in the response of the valve to close and in this way the valve does not trip during the transient pressure phases when the line is being pumped. This delay in the response to the valve is further assisted by the delay orifices 47a and _0 and also by operation of the delay facility 59 under start up conditions.

A second embodiment of the control valve 10 is illustrated in Figures 4 and 5. The control valve 10 of this embodiment is very similar to the first embodiment and like numerals have been given to like features. The second embodiment has a main S section as illustrated in Figure 4 which overlays a secondary section as illustrated in Figure The control valve 10 of the second embodiment differs from the first embodiment primarily in the location of some of the passages. In particular the secondary flow passage 49 is in communication directly with the supply inlet passage 20, and the second drive passage 66 interconnects the supply inlet passage 20 and the primary flow passage 21 rather than secondary flow passage 49 and the primary flow passage 21 as in the first embodiment.

In addition, the connecting passage 50 is formed in the second -19piston 35. Furthermore, the connecting passage interconnects the second portion 42 of the second piston to the third portion 45 rather than to the supply outlet passage 26.

Also the test flow passage extends from the spring accumulator 60 to the return outlet passage 24.

One functional difference in the second embodiment is that the second piston closes the opening 51 into supply outlet passage 22 on closing of the valve 10. In this second embodiment, the second member 38 is seated over the opening 51 in the closed position.

In other respects, the control valve 10 of the second embodiment operates in the same way as the first embodiment.

A control valve 70 according to a third embodiment of the present invention is illustrated in Figures 6 and 7.

The control valve 70 includes a fluid supply chamber 71 with °2 inlet and outlet ports 72, 73 connectable to the supply line 101 and a fluid return chamber 74 including inlet and outlet ports 75, 76 connectable to the return line 104. Both the fluid supply chamber and the fluid return chamber are cylindrical and are formed in the housing 77 of the valve such that they are coaxially aligned.

A first pressure sensitive piston 78 is located in the fluid supply chamber and is slideable therein. The piston 78 includes opposing faces 79, 80 and is arranged to separate the 30 fluid supply chamber into two separate portions; a first portion 81 which is in communication with the first face, and a second portion which is in communication with the second face.

Furthermore, the first portion of the fluid supply chamber 71 is in communication with the inlet port 72 and the second portion of the fluid supply chamber is in communication with the outlet port 73.

In a similar arrangement, the fluid return chamber includes a pressure sensitive piston 83 which is similarly slideable within the fluid return chamber. The second piston 83 includes opposing faces 84, 85 and is arranged to separate the fluid return chamber into two separate portions. The first portion 86 is in communication with the first face 84 and the second portion 87 is in communication with the second face Furthermore, the first portion 86 is in communication with the return inlet port 75 and the second portion 87 is in communication with the return outlet port 76.

The first and second pistons 78, 83 are interconnected by a rod 88 which passes through an aperture 89 located in the housing 77 and which interconnects the chambers 71, 74. A sealing ring is located in the aperture 89 to ensure that the chambers are sealed against fluid communication.

Each of the pistons 78, 83 incorporate flow passages (91, 92 respectively) which interconnect the respective faces of each piston. These flow passages thereby provide fluid communication between the respective first and second portions of each chamber.

eo In regard to the fluid supply chamber 71, the fluid passages 91 are relatively small compared to the size of the chamber such S that fluid flowing through the flow passages 91 experiences a pressure drop due to frictional forces within the passage. In this way a pressure differential is created between the first and second portions of the fluid supply chamber 71. This pressure differential casues a resultant force to be acting on the piston 78.

In a similar arrangement, the flow passages 92 located in the .eo second pressure sensitive piston 83 are small as compared to the size of the fluid return chamber 74 such that a pressure drop is experienced due to frictional forces as fluid flows from the first portion of the fluid return chamber into the second portion of the fluid return chamber. This pressure drop creates a pressure differential between the first and second portions of the fluid chamber and a resultant force act on the second piston as a result of this pressure differential.

-21- The size of the respective resultant forces acting on each of the pistons is dependent on the rate of flow of fluid through the flow passages; the larger the flow, the greater the pressure differential and therefore the greater the resultant force. Furthermore, under operating flow conditions, the resultant force acting on the first piston 78 is in a direction opposite to that of the force acting on the second piston 83.

As these forces are opposing, a net force will only act on the pistons 78, 83 if there is a difference between the size of the individual forces acting on the respective pistons.

The first and second pistons are movable together from a first position as illustrated in Figure 6, to a second position as illustrated in Figure 7. Furthermore, the pistons are biased by biasing means 93 into the first position. Typically the biasing means is in the form of a spring.

In the first position, fluid is able to flow through the supply chamber and also through the return chamber. However, in the second position, the piston 78 is movable to seat over the S outlet port 73 in the fluid supply chamber to thereby prevent S fluid flowing through the fluid supply chamber. In this way, S the control valve 70 can block the flow of fluid through the supply line.

As mentioned above, the net force acting on the pistons 78, 83 S is the difference between the forces acting on the individual pistons as a result of the pressure drop created by the 30 respective flow passages 91, 92. Consequently, the flow rate in the supply chamber which will cause the control valve 70 to close is dependent on the flow rate in the return chamber.

Under normal operating conditions, the difference between the flow rate in the fluid supply chamber and the fluid return chamber is not sufficient to create a resultant force which would move the pistons from the first position to the second position. However, if a leak becomes present in the fluid circuit, the rate of flow through the fluid return chamber -22would decrease. As a result, the amount of fluid flow required in the supply line to close the valve 70 decreases as the pressure drop across the second piston 83 is significantly less. If the flow rate in the supply line is greater than the newly established valve closure flow rate, a net force is created on the pistons which causes the pistons to move from the first position against the biasing force of the spring 93 into the second position as shown in Figure 7 to thereby prevent flow through the supply line.

The control valve further includes an adjustment device 94 which is arranged to regulate the pressure differential created in the supply chamber. The device 94 incorporates a bypass passage 95 which interconnects the first and second portions of the fluid supply chamber 71. The bypass passage 95 includes a variable valve needle 96 which is arranged to regulate the flow through the bypass passage. By being able to regulate the flow through the bypass passage, the pressure differential which is created between the first and second portions of the fluid supply chamber 71 can be varied.

S" The control device 70 further includes a reset passage 97 interconnecting the first portion 81 of the fluid supply chamber 71 and the first portion 83 of the fluid return chamber 74. The reset passage includes a valve 98 which is operable to open and close the reset passage 97. Opening of the valve 98 causes the pressure in the first portion of both the supply chamber and the return chamber to be equalized to thereby cause the piston to be moved from the second position to the first 0 0 position under the force of the biasing spring 93.

In a similar manner to the first embodiment, the configuration of the chambers, pistons and flow passages may be altered depending on the required sensitivity of the control valve Furthermore, the characteristics of the biasing means 93 in the second embodiment substantially determines the leak rate required to close off the valve Finally it is to be appreciated that various modifications -23and/or additions may be made to the control valve as disclosed herein without departing from the ambit of the present invention herein disclosed and as defined in the following claims.

*2:O 3 -24-

Claims (37)

1. A control valve for a fluid circuit having a supply line and a return line, the valve including a first passage arranged in use to be in communication with the supply line and a second passage arranged in use to be in communication with the return line and control means operable to compare the flow rates in the first and second passages, and wherein the valve is responsive to the control means and operable to prevent fluid flow in the supply line in response to a predetermined difference in the flow rates in the first and second passages.

2. A control valve as claimed in claim 1 wherein the control means compares a first passage pressure differential created by fluid flow in the first passage to a second passage pressure differential created by fluid flow in the second passage.

3. A control valve as claimed in claim 2 wherein the control means includes a o second passage pressure sensitive means responsive to the second passage pressure differential. t,

4. A control valve as claimed in claim 3 wherein the control means further includes a first passage pressure sensitive means, the first passage pressure sensitive means being responsive to the first passage pressure differential, and wherein the control means causes the control valve to become operative C *CCC4C S• to close when the difference in the size of the first passage pressure 495655 S 25 differential and the second passage pressure differential is greater than a Se predetermined level.

A control valve as claimed in claim 4 wherein the first passage includes a supply chamber with inlet and outlet ports connectable to the supply line, the second passage includes a return chamber with inlet and outlet ports connectable to the return line and wherein the second passage pressure sensitive means is located in the return chamber and the first passage pressure sensitive means is located in the supply chamber.

6. A control valve as claimed in claim 5 wherein the second passage pressure sensitive means compises a piston having opposite first and second faces, the piston being slidably mounted within the return chamber thereby separating the chamber into a first portion which is in communication with the first face and a second portion which is in communication with the second face, the second passage pressure differential being the difference between the pressure in the first and second portions in the fluid return chamber.

7. A control valve as claimed in claim 6 wherein the first portion of the return chamber is in communication with the return inlet port and the second portion of the return chamber is in communication with the return outlet port, the 15 control valve further including at least one return chamber connecting *passage interconnecting the first and second portions of the return chamber to provide fluid flow from the first portion to the second portion, the return chamber connecting passage being sized to create a pressure differential in the second passage to thereby create the second passage pressure differential, and wherein the size of the second passage pressure differential dependent on the rate of flow through the return chamber connecting o passage.

8. A control valve as claimed in claim 7 wherein the first passage pressure 25 sensitive means comprises a piston having opposite first and second faces, the piston being clidably mounted within the supply chamber thereby separating the chamber into a first portion which is in communication with the first face and a second portion which is in communication with the second face, the first passage pressure differential being the difference between the pressure in the first and second portions of the supply chamber. DIH P57530

9. A control valve as claimed in claim 8 wherein the first portion of the supply chamber is in communication with the supply inlet port and the second portion of the supply chamber is in communication with the supply outlet port, the control valve further including at least one supply chamber connecting passage interconnecting the first and second portions of the supply chamber, the supply chamber connecting passage providing fluid flow from the first portion to the second portion of the supply chamber and wherein the supply chamber connecting passage is sized to create a pressure differential in the supply chamber ccnnecting passage to thereby create the first passage pressure differential, wherein the size of the first passage pressure differential is dependent on the rate of flow through the supply chamber connecting passage.

A control valve is claimed in claim 9 wherein the first and second pistons are interconnected and movable together from a first position to a second position when the difference between the first passage and second passage pressure differentials is greater than a predetermined level.

11. A control valve as claimed in claim 10 wherein the pistons are biased into the first position such that a predetermined force is required before the pistons are able to move from the first position to the second position.

12. A control valve as claimed in claim 11 wherein the pistons are biased into the first position by a spring.

13. A control valve as claimed in any one of claims 10 to 12 wherein the supply outlet port is blocked on movement of the pistons from the first to the second position to thereby cause the flow of fluid in the supply line to be prevented.

14. A control valve as claimed in claim 13 wherein in the first position, an outer surface of the second piston is located remote from the supply outlet port and in the second position the outer surface of the second piston is arranged (J -27 T~T;, to be seated over the supply outlet port to thereby block the supply outlet port.

A control valve as claimed in any one of claims 9 to 14 further including a bypass passage interconnecting the first and second portions of the supply chamber, the bypass passage including a variable valve needle arranged to regulate the flow through the bypass passage, to thereby enable the size of the first passage pressure differential to be regulated.

16. A control valve as claimed in any one of claims 9 to 15 further including a re- set passage interconnecting the first portion of the supply chamber and the first portion of the return chamber, the re-set passage incorporating a valve arrangement wherein opening of the valve arrangement enables the pressure in the first portion of both the supply chamber and the return 15 chamber to be equalised. S

17. A control valve for a fluid circuit having a supply line and a return line, the S.. .:valve including a first passage arranged in use to be in communication with the supply I;Ne, a second passage arranged in use to be in communication 20 with the return line, and control means responsive to the rate of flow in the :second passage to establish a valve closure flow rate, and wherein when the rate of flow in the first passage is greater than or equal to the valve eo*closure flow rate, the control valve becomes operable to prevent the flow of fluid in the supply line.

18. A control valve as claimed in claim 17 wherein the control means includes second passage pressure sensitive means responsive to a first pressure differential created by fluid flow in the second passage.

19. A control valve as claimed in claim 11 or 18 further including valve means, the valve means being operable to prevent fluid flow in the supply line.

A control valve as claimed in claim 19 wherein the valve means comprises a closing device movable between an open position wherein fluid is able to flow in the supply line to a closed position wherein fluid is prevented from flowing in the supply line.

21. A control valve as claimed in claim 20 wherein the closing device includes a first passage pressure sensitive means which is responsive to a second pressure differential created by fluid flow in the first passage to move the closing device from the open position to the closed position.

22. A control valve as claimed in claim 20 wherein the closing device is biased into the open position.

23. A control valve as claimed in claim 22 wherein the control means is operable 15 to establish the valve closure flow rate by determining the magnitude of the second pressure differential.

24. A control valve as claimed in claim 23 wherein the control means is operable between a first position and a second position, and wherein in the first S: 20 position the valve closure flow rate is at a minimum and in the second position the valve closure flow rate is at a maximum, and wherein the control means is biased into the first position.

25. A control valve as claimed in claim 24 wherein the second passage pressure 25 sensitive means is responsive to the first pressure differential to locate the control means between the first and the second position.

26. A control valve as claimed in claim 25 further including a first drive passage arranged in parallel with a first section of the second passage, the first drive passage being arranged to create a third pressure differential across the first drive passage under fluid flow.

27. A control valve as claimed in claim 26 wherein the first pressure differential is the pressure drop resulting from fluid flow across the first section of the second passage.

28. A control valve as claimed in any one of claims 25 to 27 wherein the second passage pressure sensitive means is operable to vary the resistance to flow in the first section of the second passage to thereby vary the magnitude of the first pressure differential.

29. A control valve as claimed in any one of claims 21 to 28 further including a second drive passage arranged in parallel with the first section of the first passage, the second drive passage being arranged to create a fourth pressure differential across the second drive passage under fluid flow.

30. A control valve as claimed in claim 29 wherein the second pressure :o differential is the pressure drop resulting from fluid flow across the first section of the first passage.

31. A control valve as claimed in claim 30 wherein the control means is operable 20 to vary the resistance to flow in the first section of the first passage to thereby vary the magnitude of the second pressure differential.

32. A control valve as claimed in claim 31 wherein when the control means is in l: the first position, the first section of the first passage is blocked by the control S 25 means thereby causing the magnitude of the second pressure differential to be at a maximum, and in the second position, the control means is remote from the first section of the first passage thereby causing the magnitude of the second pressure differential to be at a minimum.

33. A control valve as claimed in any one of claims 21 to 32 further including at least one pressure accumulator operable to influence the second pressure differential.

34. A control valve as claimed in claim any one of claims 17 to 33 wherein the valve further includes a test facility to simulate a leak in the supply line.

35. A control valve is claimed in claims 19 to 34 further including a reset facility arranged to reset the valve means.

36. A control valve for a fluid circuit having a supply line and a return line, the valve including a first passage arranged in use to be in communication with the supply line, a second passage arranged in use to be in communication with the return line, valve means operable in response to a predetermined pressure differential created under fluid flow in the first passage to close the valve and control means responsive to fluid flow in the second passage and operable to vary the magnitude to the said pressure differential created by the fluid flow in the first passage. o•

37. A control valve substantially as herein described with reference to the I accompanying drawings. 20 DATED: 16 October 1996 *a. S o PHILLIPS ORMONDE FITZPATRICK Attorneys for: MODERN DRIVE ENGINEERING PTY LTD. and PETER GRAEME WENN .i ABSTRACT A control valve for a pressurized fluid circuit is disclosed. The valve is arranged to be connected to the supply line and to the return line of fluid circuit and includes control means which is arranged to compare the flow in the supply line and the return line to enable the valve to block fluid flow in the supply line if a leak occurs in the fluid circuit. :i