GB2271625A

GB2271625A - Post-pressure compensated spool valve

Info

Publication number: GB2271625A
Application number: GB9321107A
Authority: GB
Inventors: Alvin S Rost; Donald W Tschida
Original assignee: Dana Inc
Current assignee: Dana Inc
Priority date: 1992-10-19
Filing date: 1993-10-13
Publication date: 1994-04-20
Anticipated expiration: 2013-10-13
Also published as: GB9321107D0; CA2108616A1; GB2271625B; KR940009561A; DE4335466A1; BR9304286A; JPH06236216A

Abstract

A post-pressure compensator assembly for a spool valve includes a compensator piston 53 disposed in a stepped bore 52 of a valve body 12. A spring 59 reacts between a cap 51 threaded into the bore 52 and the piston, urging it downwardly such that the rim portion 53a of the piston 53 normally seats on the step of the bore 52. Notches 53b are formed on the lower surface of the rim portion 53a, adjacent to the step of the bore, so that, fluid can flow around the piston 53 to prevent it from becoming hydraulically locked. A load sense passageway 60 is formed through the valve body 12 which communicates with a pressure fluid supply device. A check valve 55, 57 is provided in the piston 53 to prevent the fluid pressure signals of each of the work sections from interfering with each other. <IMAGE>

Description

TITLE POST-PRESSURE COMPENSATOR ASSEMBLY FOR FLUID CONTROL VALVE 2271625

BACKGROUND OF THE INVENTION

This invention relates in general to fluid control valves and in particular to an improved structure for a post-pressure compensator assembly for such a fluid control valve.

In many hydraulic and pneumatic systems, directional control valves are provided for regulating the flow of fluid from a pressurized source to one or more controlled devices. Fluid control valves of this type generally include a body having a plurality of ports provided therein. A pressure port is provided which communicates with the pressurized source, while a tank port is provided which communicates with a fluid reservoir. one or more work ports are also provided which communicate with respective controlled devices. By selectively providing communication between the various ports, the operation of the controlled devices can be regulated in a desired manner.

Most fluid control valves include a body having a bore formed therethrough. Within the bore, a spool is mounted for limited axial movement. The spool has a plurality of circumferential grooves formed thereabout. The various ports mentioned above communicate with the bore by means of respective passageways. By moving the spool axially within the bore, certain ports are placed in fluid communication with other ports. As a result. the operation of the controlled devices is regulated in a desired manner.

There are three basic types of hydraulic systems in which fluid control valves of this general type are frequently employed. These hydraulic systems are commonly 2 referred to as opened center systems, closed center systems, and load sensing systems. In an opened center system, a pump is provided which generates a flow of fluid to the control valve at a constant flow rate, regardless of the actual fluid rate required to operate the controlled device. Thus, the output pressure from the pump varies with the load imposed on the controlled device. Any excess fluid flow from the pump is circulated through the fluid control valve (through an opened center passageway formed therein) back to the pump. Opened center systems are generally inexpensive and uncomplicated, but are rather inefficient and imprecisely controllable.

In a closed center system, a pump is provided which generates a flow of fluid to the control valve at a constant output pressure, regardless of the actual fluid pressure required to operate the controlled device. Thus, the flow rate of the fluid from the pump varies with the load imposed upon the controlled device. Any excess fluid pressure from the pump is dissipated across the control valve. Closed center systems are generally fast and precisely controllable, but are also rather inefficient and relatively expensive.

In a load sensing system, a pump is provided which generates a flow of fluid to the fluid control valve at a variable flow rate and a variable output pressure, based upon the instantaneous requirements of the controlled device. This is accomplished by (1) providing a feedback signal to the pump which is representative of the fluid pressure required to operate the controlled device and (2) controlling the output pressure from the pump to be a predetermined magnitude greater than the feedback signal. By maintaining this predetermined pressure differential to be relatively small, the efficiency of the load sensing system is much higher than in opened center and closed center systems. Fluid control valves which are employed in 3 load sensing systems are generally referred to as load sensing or pressure compensating valves, i.e., valves which include a compensator structure for controlling the pressure differential thereacross and, consequently, the flow of fluid therethrough.

There are two basic types of pressure compensated fluid control valves. In pre-pressure compensated valves, the compensator is located in the fluid stream between the input pressure port of the fluid control valve and the spool. Thus, the compensator regulates the pressure of the fluid supplied to the spool to be a predetermined magnitude greater than the pressure of the fluid in the output work port. As a result, a constant pressure differential is maintained across the spool, resulting in a constant flow of fluid therethrough regardless of changing load requirements. In post- pressure compensated valves, the compensator is located in the fluid stream between the spool and the output work port of the fluid control valve. Thus, the compensator regulates the pressure of the fluid supplied from the spool to be a predetermined magnitude which is less than the pressure of the fluid at the inlet pressure port, but greater than the pressure of the fluid in the active work port. As a result, a constant pressure differential is maintained across the spool, also resulting in a constant flow of fluid therethrough regardless of changing load requirements.

A number of post-pressure compensator structures are known in the art. While known post-pressure compensator structures have been effective, it has been found that they are rather complicated, requiring a number of components and extra machining in the valve body. Consequently, such known post-pressure compensator structures have been relatively expensive and difficult to service. Thus, it would be desirable to provide an improved structure for a post-pressure compensator assembly for a fluid control 4 valve which is relative simple and inexpensive in construction and operation.

SUMMARY OF THE INVENTION

This invention relates to an improved structure for a post-pressure compensator assembly for a fluid control valve. The assembly includes a cap which is threaded into the upper portion of a stepped bore formed in a body of a work section of the fluid control valve. A compensator piston is disposed in the lower portion of the stepped bore. The compensator piston includes an upper end having an enlarged rim portion formed thereon. A spring reacts between the cap and the compensator piston, urging it downwardly within the stepped bore. Thus, the rim portion of the compensator piston is normally seated on the stepped portion of the bore. The outer diameter of the rim portion is slightly smaller than the inner diameter of the upper portion of the bore. Also, a plurality of notches are formed on the-lower surface of the rim portion, adjacent to the stepped portion of the bore. Thus, fluid can flow freely about the rim portion of the compensator piston, thereby preventing it from becoming hydraulically locked in position during use.

A load sense passageway is formed through the body of' the work section. The load sense passageway communicates with similar load sense passageways formed in the other work sections of the fluid control valve. A check valve structure is provided in the compensator piston which permits the one-way flow of fluid from the selected outlet work port to the load sense passageway, thus creating a signal which is representative of the fluid pressure at the work port. The check valve prevents the fluid pressure signals of each of the work sections from interfering with each other.

Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of a fluid control valve including a plurality of individual work sections, each containing an improved pressure compensator assembly in 10 accordance with this invention.

Fig. 2 is a top plan view of the fluid control valve illustrated in Fig. 1.

Fig. 3 is an enlarged sectional elevational view taken along line 3-3 of Fig. 2.

Fig. 4 is an enlarged sectional elevational view of the pressure compensator assembly illustrated in Fig. 2, wherein the compensator piston is shown in a closed position.

Fig. 5 is an enlarged sectional elevational view similar to Fig. 4, wherein the compensator piston is shown in an opened position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, there is illustrated in Figs. 1 and 2 a fluid control valve, indicated generally at 10, in accordance with this invention. The illustrated fluid control valve 10 is of a sectional body design, having an inlet end cover 11, first and second individual work sections 12 and 13, and an outlet end cover 14. The inlet end cover 11 is formed having an inlet pressure port 11a which is adapted to communicate with a conventional variable flow rate, variable output pressure pump (not shown). The work sections 12 and 13 are formed having respective first and second work ports 12a, 12b and 13a, 13b which are adapted to communicate with respective 6 controlled devices (not shown). The outlet end cover 14 is typically formed having an outlet tank port which is adapted to communicate with a fluid reservoir (not shown). As will be explained in detail below, each of the work sections 12 and 13 can be controlled so as to selectively provide communication between the pressure port lla, the work ports 12a, 12b, 13a, 13b, and the tank port 14a so as to regulate the operation of the controlled devices in a desired manner.

If desired, the fluid control valve 10 may be provided with one or more additional work sections (not shown) beyond those illustrated in Figs. 1 and 2. These additional work sections permit the fluid control valve 10 to control the operation of additional respective controlled devices. Alternatively, instead of being formed in a sectional body design, the fluid control valve 10 may be formed in a unitary body design. In unitary body design, a single cast housing contains all of the components for each of the work sections contained therein.

Referring now to Fig. 3, the structure of the first work section 12 is illustrated in detail. As shown therein, the first work section 12 includes a body 20 having a transverse bore 21 formed therethrough. An elongated cylindrical spool 22 is disposed within the bore 21 for axial movement relative to the body 20. The opposed ends of the spool 22 extend outwardly from the body 20. A pair of solenoid actuated valve assemblies 23 and 24 are mounted on the opposed sides of the body 20, extending over the ends of the spool 22. The solenoid actuated valve assemblies 23 and 24 are conventional in the art and form no part of this invention. Briefly, however, such solenoid actuated valve assemblies 23 and 24 are provided to effect axial movement of the spool 22 from the centered neutral position illustrated in Fig. 3. Thus, when it is desired to shift the spool 22 axially to the right from the 7 illustrated neutral position, the left solenoid actuated valve assembly 23 is energized. conversely, when it is desired to shift the spool 22 axially to the left from the illustrated neutral position, the right solenoid actuated valve assembly 24 is energized.

The body 20 of the first work section 12 is formed having'an inlet chamber 25 (commonly referred to as a power core) which communicates with the inlet pressure port lia of the inlet end cover 11. Thus, pressurized fluid from the pump is constantly supplied to the inlet chamber 25. The body 20 is further formed having an intermediate chamber 26. The intermediate chamber 26 selectively communicates with the inlet chamber 25 by means of first and second metering notches 27 and 28 formed in the spool 22. When the spool 22 is in the neutral position illustrated in Fig. 3, communication between the inlet chamber 25 and the intermediate chamber 26 is not permitted. When the spool 22 is moved toward the right as described above, communication between the inlet chamber 25 and the intermediate chamber 26 is provided through the first metering notch 27. When the spool 22 is moved toward the left as described above, communication between the inlet chamber 25 and the intermediate chamber 26 is provided through the second metering notch 28.

A pressure compensator assembly, indicated generally at 50, is disposed within the intermediate chamber 26. The structure and operation of the pressure compensator assembly 50 will be described in detail below. The pressure compensator assembly 50 provides communication between the intermediate chamber 26 and first and second pressure loop passageways 30 and 31. The pressure loop passageways 30 and 31 selectively communicate with the work ports 12a and 12b, respectively, by means of first and second annular recesses 32 and 33 formed in the spool 22.

8 When the spool 22 is in the neutral position illustrated in Fig. 3, communication between the first pressure loop passageway 30 and the first work port 12a is not permitted. Similarly, communication between the second pressure loop passageway 31 and the second work port 12b is not permitted. When the spool 22 is moved toward the right as described above, communication between the second pressure loop passageway 31 and the second work port 12b is provided through the second annular recess 33. However, communication between the first pressure loop passageway 30 and the first work port 12a is not permitted. Rather, the first work port 12a is vented through the first annular recess 32 to a first outlet chamber 34 which communicates with the outlet tank port 14a.

Similarly, when the spool 22 is moved toward the left as described above, communication between the first pressure loop passageway 30 and the first work port 12a is provided through the first annular recess 32. However, communication between the second pressure loop passageway 31 and the second work port 12b is not permitted. Rather, the second work port 12b is vented through the second annular recess 33 to a second outlet chamber 35 which communicates with the outlet tank port 14a. In this manner, the work ports 12a and 12b are selectively placed in communication with the pressurized fluid from the inlet pressure port Ila and vented through the outlet pressure port 14a to operate the controlled device connected thereto.

Referring now to Fig. 4, the structure of the pressure compensator assembly 50 is illustrated in detail. As shown therein, the pressure compensator assembly 50 includes a cap 51 which is threaded into the upper portion of a stepped bore 52 formed in the body 20 of the first work section 12. The stepped bore 52 communicates with the intermediate chamber 26 and with the first and second 9 pressure loop passageways 30 and 31. A compensator piston 53 is disposed in the lower portion of the stepped bore 52. The compensator piston 53 includes an upper end having an enlarged rim portion 53a formed thereon. The rim portion 53a of the compensator piston 53 is normally seated on the stepped portion of the bore 52, as will be explained below. The outer diameter of the rim portion 53a is slightly smaller than the inner diameter of the upper portion of the stepped bore 52. Also, a plurality of recesses 53b (only one is illustrated) are formed on the lower surface of the rim portion 53a, adjacent to the stepped portion of the bore 52. The purpose of the rim portion 53a and the recesses 53b will be explained below.

The compensator piston 53 further includes a lower end having a plurality of metering notches 53c (only one is illustrated) formed therein. The purpose of these metering notches 53c will also be explained below. The upper end of the compensator piston 53 further has a countersink 54 formed therein. A stepped passageway 55 is formed through the lower end of the countersink 54. The stepped passageway 55 communicates with a transverse passageway 56 formed through the lower end of the compensator piston 53. A ball 57 is disposed within the stepped passageway 55 and is retained therein by a retainer plate 58. The retainer plate 58 lies flat against the bottom of the countersink 54. A spring reacts between the cap 51 and the retainer plate 58. As a result, the retainer plate 58 and the compensator piston 53 are both urged downwardly within the stepped bore 52. The ball 57 disposed within the stepped passage-way 55 functions as a check valve, allowing fluid to flow upwardly from the transverse passageway 56 into the countersink 54, but not downwardly in the reverse direction. The purpose of this check valve structure will be explained below.

A load sense passageway 60 is formed through the body 20 of the first work section 12. The load sense passageway 60 communicates with the transverse passageway 56 by means of the check valve structure discussed above. The load sense passageway 60 also communicates with a similar load sense passageway (not shown) formed in the second work section 13. As will be explained below, fluid is provided in the load sense passageway 60 at a pressure which is representative of the largest pressure sensed at any of the work ports 12a, 12b, 13a, and 13b. This fluid pressure in the load sense passageway 60 is fed back as a signal to control the operation of the variable flow rate, variable output pressure pump, as discussed above.

The operation of the fluid control valve 10 will now be explained. As mentioned above, when the spool 22 is in the neutral position illustrated in Fig. 3, communication is not permitted between the inlet chamber 25 and the intermediate chamber 26. Consequently, no pressurized fluid can flow into the compensator assembly 50. Thus, the compensator piston 53 is urged downwardly by the spring 59 to the closed position illustrated in Fig. 4. The enlarged diameter rim portion 53a of the compensator piston 53 engages the step of the bore 52, thereby functioning as a positional stop when the compensator piston 53 is moved to the closed position. Inasmuch as the transverse passageway 56 is not in communication with the pressure loop passageways 30 and 31, no pressurized fluid is supplied through the check valve structure (formed by the stepped passageway 55 and the ball 57) to the load sense passageway 60.

When the spool 22 is moved toward the right as described above, communication is permitted from the inlet chamber 25 through the intermediate chamber 26 into the lower end of the stepped bore 52. Such pressurized fluid urges the compensator piston 53 upwardly against the urging 11 of the spring 59 to the opened position illustrated in Fig. 5. In that position, the pressurized fluid flows upwardly through the metering notches 53c and into pressure loop passageways 30 and 31. As discussed above, communication between the second pressure loop passageway 31 and the second work port 12b is provided through the second annular recess 33. However, communication between the first pressure loop passageway 30 and the first work port 12a is not permitted.

Some of the pressurized fluid also flows through the transverse passageway 56, upwardly through the stepped passageway 55, around the ball 57, through the retainer plate 58 and the countersink 54, and into the upper portion of the stepped bore 52. As mentioned above, the load sense passageway 60 communicates with the upper portion of the stepped bore 52. As a result. pressurized fluid flows into the load sense passageway 60. This provides the above mentioned feedback signal (which is representative of the pressure at the selected work port 12b) for controlling the operation of the variable flow rate, variable output pressure pump.

The pressure compensator assembly 50 is located in the fluid stream between the spool 22 and the work ports 12a and 12b. Thus, the pressure compensator assembly 50 functions as a post-pressure compensator, regulating the pressure of the fluid supplied from the spool 22 to be a predetermined magnitude which is less than the pressure of the fluid at the inlet pressure port 11a. but greater than the pressure of the fluid in the active work port 12a or 12b. As a result, a constant pressure differential is maintained across the spool, also resulting in a constant flow of fluid therethrough regardless of changing load requirements. This is accomplished by means of the compensator piston 53 under the urging of the spring 59.

12 For example, assume that the fluid pressure requirement-of the selected work port 12b is 1000 p.s.i. (approximately 70 bar), as determined by the pressure of the fluid in the load sense passageway 60. Further, assume that the pump is arranged to generate an output pressure which is 300 p.s. i. (approximately 21 bar) greater than the fluid pressure requirement, or 1300 p.s.i.-(approximately 91 bar). Lastly, assume that the spring 59 is sized to generate and maintain a pressure differential of 200 p.s.i.

(approximately 14 bar) across the spool 22. Under these conditions, the pressure of the fluid in the inlet chamber is 1300 p.s.i. (approximately 91 bar), while the pressure of the fluid in the intermediate chamber 26 is 1100 p.s.i. (approximately 76 bar). Consequently, the pressure differential across the spool 22 between the inlet chamber 25 and the intermediate chamber 26 is 200 p.s.i. (approximately 14 bar).

Now assume that the fluid pressure requirement of the selected work port 12b changes from 1000 p.s.i.

(approximately 70 bar) to 1100 p.s.i. (approximately 77 bar). Because of this, the pump increases the output pressure to 1400 p.s.i. (approximately 97 bar). Under these conditions, the pressure of the fluid in the inlet chamber is 1400 p.s.i. (approximately 97 bar), while the pressure of the fluid in the intermediate chamber 26 is 1200 p.s.i. (approximately 83 bar). Consequently, the pressure differential across the spool 22 between the inlet chamber 25 and the intermediate chamber 26 remains at 200 p.s.i. (approximately 14 bar). It can be seen, therefore, that the pressure compensator assembly 50 maintains a constant pressure differential across the spool 22 regardless of the changing pressure requirements at the selected work port 12b. As a result, the flow of fluid across the spool 22 is also maintained constant during use.

13 As mentioned above, the ball 57 disposed within the stepped passageway 55 functions as a check valve, allowing fluid to flow upwardly from the transverse passageway 56 into the countersink 54 and the load sense passageway 60, but not downwardly in the reverse direction. Because the transverse passageway 56 is now in communication with the pressure loop passageways 30 and 31, pressurized fluid is supplied through the check valve structure (formed by the stepped passageway 55 and the ball 57) to the load sense passageway 60. Using the figures provided in the first assumption above, therefore, a fluid pressure signal of 1000 p.s.i. (approximately 70 bar) is fed through the check valve structure to the load sense passageway 60.

The check valve structure of the stepped passageway 55 and the ball 57 prevents the fluid pressure signals from the second work section 13 from interfering with fluid pressure signal from the first work section 12. As discussed above, the ultimate load sense signal generated by the fluid control valve 10 is preferably representative of the highest pressure requirement of any of the individual work sections 12 and 13. When the pressure requirement of the first work section 12 is smaller than the pressure requirement of the second work section 13, the cheek valve structure permits the pressure of the fluid in the load sense passageway 60 to be greater than the pressure of the fluid in the pressure loop passageways 30 and 31. This prevents the lower pressure requirement of the first work section 12 from reducing the pressure of the fluid in the load sense passageway 60 to its lower magnitude.

As previously discussed, the outer diameter of the rim portion 53a of the compensator piston 53 is slightly smaller than the inner diameter of the upper portion of the stepped bore 52. Also, a plurality of recesses 53b (only one is illustrated) are f ormed on the lower surf ace of the 14 rim portion 53a, adjacent to the stepped portion of the bore 52. This structure is provided to permit fluid to flow freely about the side of the rim portion 53a of the compensator piston 53 and into the recesses 53b formed on the lower surface thereof. As a result, the compensator piston 53 is prevented from becoming hydraulically locked in position during certain usage conditions.

For example, assume that the first work section 12 is initially deactivated, while the second work section 13 is activated to elevate a load. As a result, there is pressurized fluid in the load sense passageway 60 having a pressure equal to the pressure requirement at the work port 13a. This pressure is exerted against the upper surface of the compensator piston 53 in the first work section 12, tending to urge it downwardly in the seated position illustrated in Fig. 4. If it is subsequently desired to activate the first work section 12 at a lower pressure requirement than the second work section 13, it is possible that the compensator piston 53 may not respond immediately when the spool 22 is moved. This is because the pressure exerted by the fluid in the load sense passageway 60 acts against the larger upper surface of the rim portion 53a of the compensator piston 53. To prevent this from occurring, the recesses 53b permit the high pressure fluid in the load sense passageway 60 to flow beneath the rim portion 53a. As a result. any pressure differential across the rim portion 53a of the compensator piston 53 which would tend to maintain the compensator piston 53 closed is relieved.

It should be noted that the compensator piston 53 functions as a load check device for the fluid control valve 10. For example, assume the first work section 12 is initially activated to elevate a load to a certain height, then de-activated to maintain the load at that height. To accomplish this, the compensator piston 53 is initially opened as shown in Fig. 5 to elevate the load, then closed 9 as shown in Fig. 4 to maintain it at the desired height. Assume further that the second work section 13 is subsequently activated to operate a second controlled device at a lower pressure requirement than the first work section 12. Because of the pressure differential between the two work sections 12 and 13 (transmitted through the load sense passageway 60), the compensator piston 53 in the second work section 13 is maintained closed until the fluid pressure in the intermediate chamber therein is raised to the higher pressure requirement of the first work section 12. This prevents the load carried by the first work section 12 from dropping suddenly when the second work section 13 is activated.

The fluid control valve 10 operates as described above so long as the total fluid pressure requirements of the entire system do not exceed the capacity of the pump. If the fluid pressure requirements of the system exceed the capacity of the pump, the fluid control valve 10 will automatically operate in a proportioning mode. In this mode, fluid is fed proportionately to each of the work sections 12 and 13. This occurs because all of the compensator pistons 53 are open, and the load sense passageway 60 equalizes the fluid pressure in each of the work sections 12 and 13.

The fluid control valve 10 of this invention is advantageous because all of the components thereof relating to the above-discussed load check and load sensing functions are located within the compensator assembly 50.

Thus, the structure of this invention is simpler and less expensive than known post-pressure compensator structures. Also, all of such components are readily accessible from the top of the fluid control valve 10, facilitating maintenance and service.

In accordance with the provisions of the patent statutes, the principle and mode of operation of this 16 invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise as specifically explained and illustrated without departing from its spirit 5 or scope.

p 17

Claims

What is claimed is:

1. A fluid control valve comprising:

a valve body including an inlet chamber adapted to communicate with a source of pressurized f luid and a work port adapted to communicate with a controlled device; bore formed in said valve body communicating with said inlet chamber and said work port; spool disposed within said bore and movable between a first position, wherein communication between said inlet chamber and said work port is prevented, and a second position, wherein communication between said inlet chamber and said work port is permitted; and a pressure compensator assembly disposed between said spool and said work port.

2. The fluid control valve defined in Claim 1 further including an intermediate chamber formed in said valve body and communicating with said bore and said work port, and wherein said pressure compensator assembly is disposed in said intermediate chamber.

3. The fluid control valve defined in Claim 1 wherein said pressure compensator assembly includes a compensator piston disposed in a piston bore providing communication between said inlet chamber and said work port, said compensator piston being movable between a closed position, wherein communication between said piston bore and said work port is prevented, an opened position, wherein communication between said piston bore and said work port is permitted.

4. The fluid control valve defined in Claim 3 wherein said valve body further includes a load sense passageway for providing a signal which is representative of the fluid pressure at the work port, and wherein said compensator piston includes means for 18 providing one-way communication from said work port to said load sense passageway when said compensator piston is in said opened position.

5. The fluid control valve defined in Claim 4 wherein said means for providing one-way communication includes a check valve provided in said compensator piston.

6. The fluid control valve defined in Claim 3 further including means for urging said compensator piston toward said closed position.

7. The fluid control valve defined in claim 3 wherein said compensator piston has at least one metering notch formed in a surface thereof, communication between said piston bore and said work port being provided through said metering notch when said compensator piston is in said opened position.

8. The fluid control valve defined in Claim 1 further including a second work port adapted to communicate with a controlled device, said spool being movable between a first position, wherein communication between said inlet chamber and either of said first and second work ports is prevented, a second position, wherein communication between said inlet chamber and said first work port is permitted while communication between said inlet chamber and said second work port is prevented, and a third position, wherein communication between said inlet chamber and said first work port is prevented while communication between said inlet chamber and said second work port is permitted.

9. The fluid control valve defined in Claim 8 further including an intermediate chamber formed in said valve body and communicating with said bore and each of said work ports, and wherein said pressure compensator assembly is disposed in said intermediate chamber.

1 1 19

10. The fluid control valve defined in Claim 8 wherein said pressure compensator assembly includes a compensator piston disposed in a piston bore providing communication between said inlet chamber and each of said work ports, said compensator piston being movable between a closed position, wherein communication between said piston bore and each of said work ports is prevented, and an opened position, wherein communication between said piston bore and each of said work ports is permitted.

11. A fluid control valve substantially as described herein with reference to, and as shown in, the accompanying drawings.