GB1594268A

GB1594268A - Control valves

Info

Publication number: GB1594268A
Application number: GB3558177A
Authority: GB
Original assignee: Shoketsu Kinzoku Kogyo KK
Current assignee: Shoketsu Kinzoku Kogyo KK
Priority date: 1976-08-25
Filing date: 1977-08-24
Publication date: 1981-07-30

Description

(54) IMPROVEMENTS IN OR RELATING TO CONTROL VALVES (71) We, SHOKETSU KINZOKU KOGYO KABUSHIKI KAISHA, a Japanese company, of 13 12, Shinbashi l-chome, Minato-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to control valves for use in a fluid-pressure operating system and more particularly but not exclusively is concerned with a control valve positioned between a flow direction-changeover valve and an actuator.A control valve according to the invention may prevent an impulsive operation of an actuator by slowing down the movement of a piston under a meter-in control, as, for example, at the start of an operation when there is no fluid pressure in the actuator, and yet may allow normal movement of a piston during the operation.

Hitherto, for adjusting the speed of a piston reciprocating within a cylinder in an actuator, a meter-out control system has been adopted for a speed controller. However, the meter-out control system has the disadvantage that, for instance, after the operation, or during checking of the equipment, the pressure within the cylinder remains at an atmospheric pressure level which disables the speed control of the piston as the speed control of a piston is applied to the controller. As a result. this often leads to a damage of fixtures or the like or injury of an operator.

Accordingly, an operator should pay close attention to the operation at the beginning thereof, so that the efficiency of the operation is lowered.

For the aforesaid reasons, the speed controller is used in a meter-in control mode.

Although this attempt is partially successful in preventing the impulsive movement of the piston at the commencement of operation, it suffers from the disadvantage that it takes an excessively long time for the fluid pressure within a cylinder to build up, and hence the speed of the piston is lowered, so that there arises a delay in transmission of pressure, with an accompanying loss in operating efficiency.

According to one aspect of the present invention there is provided a control valve comprising: a body provided with two ports serving as an inlet and an outlet for fluid; a fluid passage provided in said body for interconnecting said two ports; a movable valve member positioned in said fluid passage adjacent to a valve seat, the valve member being arranged so that a primary fluid pressure at the inlet tends to displace the member away from the valve seat, and the valve member and its degree of movement being such that at one extreme of its movement it approaches the valve seat so as to provide a flow restriction for fluid in said fluid passage, and at the other extreme of its movement it is displaced away from the valve seat so as to provide substantially no restriction to the flow of fluid in the fluid passage;; resilient means acting on said valve member tending to displace said valve member towards said valve seat; and a piston responsive to a secondary fluid pressure for displacing the valve member away from said valve seat against the action of said resilient means, the arrangement being such that a secondary fluid pressure lower than the inlet pressure will suffice to oppose the action of said resilient means.

In several embodiments of the invention, the valve member at said one extreme of its movement remains clear of the valve seat, the clearance between the valve member and the valve seat providing the flow restriction.

In another embodiment, the valve member is provided with a bypass channel or bore and in this embodiment the valve member abuts the valve seat at said one exteme of its movement; in this case, the flow restriction is effected by fluid having to pass through the bypass bore in order to pass from the inlet of the valve to the inlet of the valve to the outlet.

Advantageously, the control valve includes an adjustable member which limits the travel of the valve member.

The piston can be a pilot piston which divides a chamber within the valve into two parts, one part being in communication with a pilot port, the arrangement being such that.

in use when fluid under pressure is supplied to said pilot port the fluid pressure acting on the piston forces the piston to force the valve member away from said valve seat.

Conveniently, the resilient means which acts on the valve member is a compression spring.

In some embodiments of the invention. the piston is integral with said valve member.

With these embodiments, the control valve can be mounted in the housing of a pneumatic actuator.

For a better understanding of the present invention and to show more clearly how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which: Figure IA is a prior art pressure circuit diagram; Figures IB and IC are plots of the pressure-time variation of the circuit of Figure I A; Figures 2 and 3 are cross-sectional views of a control valve according to the first embodiment of the invention, in the varying operational conditions, with the associated fluid circuit shown diagrammatically; Figure 4 shows a cross-section of a second embodiment with the associated circuit shown diagrammatically; Figure 5 shows a cross-section of a third embodiment; Figure 6 shows a cross-section of an arrangement which does not form part of the present invention;; Figure 7A shows, diagrammatically, a fluid circuit including a control valve according to the invention; Figure 7B shows the pressure-time variation of the circuit of Figure 7A; Figure 8 shows a cross-section of a fourth embodiment: Figure 9 shows a circuit diagram which includes a control valve according to the fourth embodiment; Figures 10, 11 and 12 show the operation, under different conditions, of the control valve according to the fourth embodiment; Figure 13 is a.vertical cross-sectional view of the fifth embodiment; Figure 14 is a prior art circuit diagram; Figures 15 and 16 show the pressure-time variation of the circuit of Figure 14; Figure 17 is a circuit diagram, including a control valve according to the fifth embodiment; Figure 18 shows the pressure-time variation of the circuit of Figure 17;; Figure 19 is a cross-sectional view of the sixth embodiment of the invention; and Figure 20 is a vertical cross-sectional view of part of the seventh embodiment of the invention.

Referring to Figure IA, there is shown a prior art pneumatic circuit. Compressed air is introduced into a chamber 3 in an actuator 2 through a direction-changeover valve 1, while compressed air is discharged from the other chamber 4 in the actuator 2. As is clear from Figure IB, a piston is displaced at a given speed due to the pressure difference between the chambers 3 and 4.

However, when the direction-changeover valve I is switched from an exhaust centre neutral position, in which compressed air is exhausted from the actuator, to a position to supply compressed air to the chamber 3, then the poston is subjected to an excessively large force of compressed air flowing into the chamber 3, with the result that, as can be seen from Figure IC, the piston is moved in an impulsive manner. This can lead to damage of equipment and/or injury of the operator.

In gencral, an exhaust centre type flowdirection changeover valve is used for saftey purposes so as to prevent an accident resulting from the discharge of working fluid from an actuator when a machine is not in use.

Contrary to this there is the danger at the beginning of the operation, as has been described above.

Figures 2 and 3 shoe one embodiment of the present invention.

A body of a control valve 10 is provided with a port 12 which communates with a flow direction-changover valve 1, a port 13 which cmmunicates with one chamber 3 in an actuator 2, and a pilot port 14 which communicates with the other chamber 4 in the actuator 2. Provided inside the body of the valve 10 is a valve chamber 16 which comprises a large-diameter chamber 16a and a small-diameter chamber 16b, with a valve seat 18 defined therebetween. Further provided in the body of the valve 10 is an auxiliary chamber 17 of a large diameter, which communicates with one end of the small-diameter chamber 16b. The port 12 and port 13 communicate with the smalldiameter chamber 16b and large-diameter chamber 16a, respectively. The pilot port 14 communicates with the auxiliary chamber 17.

A valve member 19 is positioned within the valve chamber 16 forming part of a fluid passage, so as to define a clearance between itself and the valve seat 18.

A balance piston 20 is integral with the valve member 19 and is fitted, and is free to reciprocate, in the small-diameter chamber 16b. A compression spring 22 is confined between the valve member 19 and a plug member 21 which closes one end of the valve chamber 16. A pilot piston 23 of a large diameter compared to that of piston 20 and valve member 19 is slidingly fitted in the auxiliary chamber 17 and abuts the end of the balance piston 20.

The pilot port 14 communicates with the auxiliary chamber 17 on the rear side of the pilot piston 23, while a discharge port 24 communicates with the auxiliary chamber 17 on the front side of the pilot piston 23, for discharging a back pressure, when the pilot piston is displaced.

A cavity 25 is defined in the valve body 19, with one end of an adjusting rod 26 being inserted therein. The rod 26 extends through the plug body 21 slidingly. The adjusting rod 26 has a locking head portion 27 which normally abuts the wall or shoulder portion 28 of the cavity 25 under the action of the resilient spring 22. The locking head portion 27 is loosely fitted in the cavity in a manner such that it does not abut the closed end (i.e.

opposite to shoulder 28) of the cavity 25 when the valve member 19 assumes its fully open position (Figure 3), being biased by the pilot piston 23. A knob 29 is secured on the other end portion of the adjusting rod 26 and has a threaded portion which engages with a threaded portion of the plug member 21. The rotation of knob 29 allows the position of the valve body 19 to be adjusted by the adjusting rod 26, i.e. the minimum clearance defined between the valve member 19 and the valve seat 18 can be adjusted by use of the knob 29.

Figure 2 shows the first changeover position, wherein there is no pilot fluid pressure applied to the pilot port 14. In the case where the changeover valve I assumes an exhaust centre neutral position as shown, both the chambers 3, 4 in the actuator 2 are in communication with atmospheric pressure, and thus the valve member 19 is not subjected to the action of fluid pressure: thus in turn the locking head portion 27 of the adjusting rod 26 abuts the shoulder portion 28 of the cavity 25 under the action of spring 22, thereby restricting the clearance between the valve member 19 and the valve seat 18. In other words, the control valve 10 assumes the first changeover position, while the pilot piston 23 is biased to the left. being pushed by the balance piston 20.

Assume that the changeover valve I is changed over to the side A (shown by chain lines in Figure 2), so that the port 12 is in communication with a fluid source. However. the valve member 19 remains still and hence maintains the aforesaid first changeover position, because the balance piston 20 integral with the valve body 19 is biased to the left under the action of spring 22, and the pilot port 14 is in communication with the atmosphere, so that the pilot piston 23 is not moved.As a result, a control fluid introduced through the port 12 flows through a clearance between the valve member 19 and the valve seat 18, with the fluid flow rate being restricted, and then from the port 13 into the chamber 3 in the actuator 2, with the result that the piston in the actuator 2 makes a slow start due to the restricted clearance between the valve member 19 and the valve seat 18 which thus acts in a meter-in control mode.

When the direction-changeover valve 1 is switched to the position B, as shown in Figure 3, and the port 12 is brought into communication with the atmosphere while the pilot port 14 and the other chamber 4 in the actuator 2 are put into communication via a pipe 5 with a fluid source, then the pilot piston 23 is immediately moved or subject to a fluid pressure introduced through the pilot port 14 into the auxiliary chamber 17, so that the valve member 19 is forced to the right, thereby providing the second changeover position, wherein the clearance between the valve member 19 and the valve seat 18 is at a maximum. In this respect, the diameter of pilot piston 23 is sufficiently large to respond to a fluid pressure, even if the fluid pressure is quite low.As a result, fluid flows out of the chamber 3 in the actuator 2 without being subjected to any large resistance, with the result that the piston is retracted at a suitable speed in the actuator due to the difference in pressure between the chamber 3 and the chamber 4. This makes no difference to the operation of the two-port, two-way valve (Figure 1B).

In addition, when the direction-changeover valve 1 is switched from side B to side A, then the chamber 4 in the actuator 2 is kept open to the atmosphere, and fluid is introduced from a fluid source via control valve 10 into chamber 3. As has been described earlier, the pilot piston 23 is susceptible to a low level pressure, so that as there remains a pressure in the pipe 5, the pilot piston 23 maintains its biased condition (to the right), thereby maintaining the valve member 19 in its fully open position relative to the valve seat 18, with the result that the fluid is subjected to no substantial fluidic resistance when flowing into the chamber 3. Accordingly, the actuator 2 operates in the same manner as that of the ordinary two-port, twoway valve.It should be noted that after the fluid pressure in the pipe 5 has been lowered almost to atmospheric pressure. i.e. the piston in the actuator has completed its forward displacement, the valve member 19 returns to its clearance restricting position, i.e. it moves to the left.

As is apparent from the foregoing descrip tion of the control valve according to the first embodiment of the invention, the inflow of a fluid into the actuator is limited or restricted.

only when starting from an exhaust centre neutral position or from a condition where fluid pressure in the actuator is practically negligible, thereby allowing a slow start for the actuator, while, after the first stroke. the piston in the actuator may be moved or operated at a given speed, with little limitation.

Meanwhile, for changing the speed of the piston in the actuator during steady running it suffices to provide a throttle valve or speed control valve for the direction changeover valve I. Alternatively, a manually adjustable throttle valve may be incorporated into the fluid passage of the control valve 10 for a meter-out speed control.

Figure 4 shows a control valve in accordance with the second embodiment of the invention, in which the speed of the piston in the actuator 2 may be controlled both for the forward movement and for the backward movement thereof. The control valve includes two control valves 10a, lOb which are similar in construction to the control valve 10 in the first embodiment. Ports 12a, 12b communicate with the flow direction-changeover valve 1, while ports 13a, 13b communicate with chambers 3, 4 in the actuator 2, respectively. The ports 12a, 12b communicate through pilot communicating-passages 30a, 30b with auxiliary chambers 17b, 17a, respectively. The construction and operation of each valve is similar to that of the valve according to the first embodiment, and hence further description of the valves will be omitted.

The third embodiment shown in Figure 5 differs from the first embodiment in the construction of the valve body 19 relative to the pilot piston 23, and the relative position of the port 12 and port 13, and in that spring 22 is confined between the adjusting rod 26 and the valve member 19, although the functions of the valve are similar to the first embodiment. However, in this embodiment, the valve member 19 and the valve seat 18 provides a fully open position or maximum clearance, upon completion of operation, when the direction-changeover valve 1 is returned from the changeover position A or B to its neutral position, while the first embodiment of the invention assumes a clearance restricted position. Selection between the first and third embodiment depends on the loading mode of the actuator.

Figure 6 shows a comparative control valve which forms no part of the invention.

Valve chamber 16 provided in the body of the control valve consists of a large-diameter chamber 16a and a small-diameter chamber 16b, with a by-pass running therebetween.

An auxiliary valve seat 31 which cooperates with a variable throttle valve member 33 is provided in the bypass. The position of the valve member 33 is adjustable by means of a knob 32, thereby restricting the flow of a fluid under the cooperation of the valve seat 3 1 with the variable throttle valve member 33. Upon starting operation of the actuator, a fluid is introduced from the port 12 through a clearance defined between the variable valve member 33 and the auxiliary valve seat 31 and then through the outlet 13 into the actuator, thereby starting the actuator slowly.

Figures 7A and 7B illustrate a fluid circuit containing a valve 10 of this invention and are analogous to Figures 1A, 1B and IC.

Meanwhile, the control valve according to the present invention may be connected to a speed control valve, changeover valve or actuator. However, these components may be incorporated into a single valve body so as to provide a composite valve construction.

Figure 8 shows a control valve according to the fourth embodiment of the invention. A body 101 is provided with ports 102, 103 as inlet and outlet for a fluid. The ports 102, 103 are interconnected by a fluid passage 104, in which there is provided a two-port, two-way valve 105 of a spring-offset pilot type, serving as a flow rate control valve, and a needle valve 106 serving as a throttle valve, in the form of a composite main valve 107. In addition, a check valve 108 is provided in series with the composite main valve 107.

Description will begin with the arrangement of the composite main valve 107. A valve member 110 cooperates with a valve seat 109 formed in the body 101. A piston 111 is integral with the valve member 110.

The piston 111 is slidingly fitted in a cylinder 112 in a fluid-tight manner. An internallythreaded cylindrical wall 113 extends from the cylinder 112, and a closure member 114 is fitted in the wall 113. A spring 115 is confined between the piston 111 and the seat member 114.

In the two-port-two-way valve 105, a pressure prevailing in the port 103 is applied to the piston 111 as a pilot pressure, so that the valve member 110 departs from the valve seat 109 against the action of the spring 115, thereby opening the passage 4. A needle valve 106 is built in the valve 105. A needle 120 is movable in a passage 116 running through a central portion of the valve member 110 and the piston 111. A tip portion 117 of needle 120 may vary the size of an opening defined between a transverse passage 118 in the valve member 110 and the passage 116.

The rear end portion of the needle valve 120 is threaded as at 121, the threaded portion 121 is threaded into a threaded hole 122 defined in closure member 114, with the outer end of the threaded portion 121 projecting externally of the body of the valve. A slot 123 is provided in the aforesaid outer end of the threaded portion 121 so that it can be adjusted by a screw driver.

Description will be given of check valve 108.

A check valve is provided on the fluid passage 104 in series relation to the composite main valve 107. The check valve includes a valve seat 124, a valve member 125 which cooperates with the valve seat 124, a spring 126 for forcing the valve member 125 against the valve seat 124, and a push rod 127 for use in keeping the valve member 125 off the valve seat 124. The push rod 127 is coupled to a threaded cylindrical member 129 which engages with an internally-threaded cylindrical wall 128 forming part of the body 101.

Defined in an end face of the threaded cylindrical member 129 is a slot 130, into which the tip of a screw driver can be fitted.

Shown in Figure 9 is a piston 133 in an actuator 131 which divides the interior of a cylinder 132 into a headside chamber and a rod-side chamber. A pipe 134 is connected to the head-side chamber and to the port 103.

The port 102 is connected to a pipe 136 communicates with a solenoid operated valve 135. A pipe 138 leads from the rod-side chamber 137 of the cylinder 132 to the valve 135 via speed controller 139 which provides a meter-out control. The speed controller 139 comprises a variable throttle 140 arranged in parallel with a check or non-return valve 141.

With this circuit arrangement, when a fluid is supplied from the port 103 towards the cylinder 132, as shown in Figure 10. the fluid slowly flows through a restricted opening defined by the needle 120 in the needle valve 106 and then through a clearance defined between the valve member 125, which is pushed by the push rod 127, and the valve seat 124 so that the piston 133 in the cylinder 132 moves slowly.

Figure 11 shows the condition where the piston rod 137 is pushed out. In this case, the pressure of fluid supplied to the port 102 is higher than a pressure set by the spring 115, with the result that the changeover valve 105 in the composite main valve 107 is brought to its fully open position, so that the speed of piston 133 in the cylinder 132 is controlled by the speed controller 139 connected to the rod side chamber, independently of the control valve according to the present invention.

When the piston rod 137 is retracted, as shown in Figure 12, the changeover valve 105 in the composite main valve 107 maintains its fully open position due to the pressure on the head side of the chamber, i.e.

at the port 103, so that the speed of piston 133 in the cylinder 132 is controlled by the opening in the check valve 108. i.e. the clearance defined between the valve member 125 and the valve seat 124.

Figures 13 to 18 illustrate the fifth embodiment if the invention.

Reference will now be made to Figures 13 to 18. Shown in Figure 13 is a body 201 of a control valve. The body 201 is provided with a port 202 connected to a flow directionchangeover valve, and a part 203 connected to a cylinder in an actuate. A fluid passage 204 in the body 201 interconnects the ports 202 and 203. A throttle valve 205 and a pressure control valve 206 are provided in series in the passage 204 which connects the port 202 to the port 203. The throttle valve 205 restricts the flow of a fluid due to a clearance defined between a valve member 207 and a valve seat 208, when fluid flows from the port 203 towards the port 202.

However, the throttle valve 205 does not restrict the flow of a fluid, when flowing from the port 202 towards the port 203, because the valve stem 209 is loosely fitted in a central hole 207', with the result that the valve body 207 is simply pushed downwards, leaving ample clearance for the fluid. The valve stem 209 protrudes outside the body 201 and is threaded into a seat member 210 provided in the body 201. By rotating a screw driver, with the tip thereof fitted in the slot 211 defined in the end face of valve stem 209, the stem 209 may be moved in or out of the seat member 210, thereby adjusting the minimum clearance between the valve member 207 and the valve seat 208.

A pressure-adjusting valve 206 comprises a valve member 213 and a corresponding valve seat 212, a piston integral with the valve member 213, and a pressure adjusting spring 216 confined between the piston 214 and a pressure adjusting member 215. When a pressure prevailing on the side of the port 203 exceeds a given level set by the pressure adjusting spring 216, the valve member 213 lifts off the seat 212, and retracts with the piston 214. In this embodiment, however, a narrow passage 217 is provided in the valve member 213, through which a small amount of fluid may pass.By rotating a screw driver, with the tip thereof being fitted in a slot 218 provided in the end face of the pressureadjusting member 215, the pressure adjusting member 215 threaded into the body 201 may be moved relative to the body 201, so that the force of the pressure adjusting spring 216 may be adjusted, thereby adjusting a preset pressure level.

With the circuit arrangement shown in Figure 17, there is no possibility that in the initial phase of operation under a meter-out control mode, a pressure fluid is abruptly supplied into the cylinder chamber and thus causes an impulsive movement of the piston.

In other words, in the starting phase of operation, a small amount of fluid flows (in the direction of the arrows shown in Figure 13) through the narrow passage 217, and then the valve member 213 is brought to its fully open position, as the pressure on the side of port 203 is gradually built-up. thus providing a desired safe speed for the piston.

Figure 18 depicts the resultant behaviour of the piston, which may be compared with the prior art arrangements illustrated by Figures 14 to 16.

Referring to Figure 19 there is shown a cylinder 401 of an actuator. A piston 402 is fitted in the cylinder 401 slidingly along the inner surface of the cylinder 401. there being an hermatic seal between the piston 402 and the cylinder 401. A piston rod connected to the piston 402 protrudes from the cylinder 401 so that the movement of piston rod 403 is converted into work required.

The opposite ends of the cylinder 401.

whose interior is partitioned by the piston into two chambers 404, 405, are closed with plugs 406, 407. In this embodiment, a control valve 408 is incorporated in the plug 406 which closes the head side chamber. The control valve 408 may alternatively be incorporated in the plug 407 on the side of the rod 403. Furthermore, control valves 408 may be incorporated in both the plugs 406, 407 if desired.

The control valve 408 comprises a valve member 412 positioned in a passage 410 interconnecting the chamber 404 and a port 409 provided in the plug 406, so as to provide a restricted passage 411; and a pressureresponsive member 413 which stops the restricting function of the valve member 412, when pressure in the passage 410 exceeds a certain level. The pressure-responsive member 413 comprises a piston member 414 integral with the valve member 412, a spring 415 confined between the piston member 414, and a seat 416.

A port 417 in the plug 407 communicates with the chamber 405.

With the aforesaid circuit arrangement, speed controllers 420, 421 are provided on supply pipes 418, 419 leading from the flow direction-changeover valve to their respective ports 409, 417. A fluid under pressure which has been supplied from the directionchangeover valve through the pipe 418 into the port 409 is introduced through a clearance defined between the valve member 412 and a valve seat cooperative therewith, i.e.

through the narrow passage 411 into the chamber 404. Due to a pressure rise in the chamber 404, the piston member 414 moves so that the valve body 412 departs from its seat, after which fluid is supplied in the fully open condition of the passage 410, thereby accelerating the movement of piston 402. In the case when the piston 402 is displaced in the opposite direction, the valve body 412 functions in a meter-out control mode, thereby suppressing impulsive movement of the piston 402.

According to the seventh embodiment of the invention, as shown in Figure 20, a valve stem 422 is secured to the valve member 412, and extends through the piston member 414 and a plug 416, and protrudes externally thereof. A threaded portion 423 formed on part of the valve stem 422 is fitted in a threaded hole 424 provided in the seat 416.

By inserting and rotating the tip of a screwdriver into a slot 425 defined in the end face of valve stem 422, the valve member 412 may be moved back and forth, thereby adjusting the opening of the narrow passage 411. The other components are similar to those in the embodiment of Figure 19.

WHAT WE CLAIM 1S:- I. A control valve comprising: a body provided with two ports serving as an inlet and an outlet for a fluid; a fluid passage provided in said body for interconnecting said two ports; a movable valve member positioned in said fluid passage adjacent to a valve seat, the valve member being arranged so that a primary fluid pressure at the inlet tends to displace the valve member away from the valve seat, and the valve member and its degree of movement being such that at one extreme of its movement it co-operates with the valve seat to provide a flow restriction for fluid in said fluid passage, and at the other extreme of its movement it is displaced away from the valve seat so as to provide substantiallv no restriction to the flow of fluid in the fluid passage;; resilient means acting on said valve member tending to displace said valve member towards said valve seat; and a piston responsive to a secondary fluid pressure for displacing the valve member away from said valve seat against the action of said resilient means, the arrangement being such that a secondary fluid pressure lower than the inlet pressure will suffice to oppose the action of said resilient means.

2. A control valve as claimed in claim 1, wherein at said one extreme of its movement the valve member remains clear of the valve seat, the clearance between the valve member and the valve seat providing said flow restriction.

3. A control valve as claimed in claim 1, wherein the valve member is provided with a bypass bore and wherein at said one extreme of its movement, the valve member abuts the valve seat, the said bypass bore providing said flow restriction.

4. A control valve as claimed in claim 1, 2 or 3, and further including an adjustable member which limits the travel of the valve member.

5. A control valve as claimed in claim 1, 2, 3 or 4, wherein the piston is a pilot piston which divides a chamber within the valve into two parts, one part being in communication with a pilot port, the arrangement being

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

side of port 203 is gradually built-up. thus providing a desired safe speed for the piston.

Figure 18 depicts the resultant behaviour of the piston, which may be compared with the prior art arrangements illustrated by Figures 14 to 16.

Referring to Figure 19 there is shown a cylinder 401 of an actuator. A piston 402 is fitted in the cylinder 401 slidingly along the inner surface of the cylinder 401. there being an hermatic seal between the piston 402 and the cylinder 401. A piston rod connected to the piston 402 protrudes from the cylinder 401 so that the movement of piston rod 403 is converted into work required.

The opposite ends of the cylinder 401.

whose interior is partitioned by the piston into two chambers 404, 405, are closed with plugs 406, 407. In this embodiment, a control valve 408 is incorporated in the plug 406 which closes the head side chamber. The control valve 408 may alternatively be incorporated in the plug 407 on the side of the rod 403. Furthermore, control valves 408 may be incorporated in both the plugs 406, 407 if desired.

The control valve 408 comprises a valve member 412 positioned in a passage 410 interconnecting the chamber 404 and a port 409 provided in the plug 406, so as to provide a restricted passage 411; and a pressureresponsive member 413 which stops the restricting function of the valve member 412, when pressure in the passage 410 exceeds a certain level. The pressure-responsive member 413 comprises a piston member 414 integral with the valve member 412, a spring 415 confined between the piston member 414, and a seat 416.

A port 417 in the plug 407 communicates with the chamber 405.

With the aforesaid circuit arrangement, speed controllers 420, 421 are provided on supply pipes 418, 419 leading from the flow direction-changeover valve to their respective ports 409, 417. A fluid under pressure which has been supplied from the directionchangeover valve through the pipe 418 into the port 409 is introduced through a clearance defined between the valve member 412 and a valve seat cooperative therewith, i.e.

through the narrow passage 411 into the chamber 404. Due to a pressure rise in the chamber 404, the piston member 414 moves so that the valve body 412 departs from its seat, after which fluid is supplied in the fully open condition of the passage 410, thereby accelerating the movement of piston 402. In the case when the piston 402 is displaced in the opposite direction, the valve body 412 functions in a meter-out control mode, thereby suppressing impulsive movement of the piston 402.

According to the seventh embodiment of the invention, as shown in Figure 20, a valve stem 422 is secured to the valve member 412, and extends through the piston member 414 and a plug 416, and protrudes externally thereof. A threaded portion 423 formed on part of the valve stem 422 is fitted in a threaded hole 424 provided in the seat 416.

By inserting and rotating the tip of a screwdriver into a slot 425 defined in the end face of valve stem 422, the valve member 412 may be moved back and forth, thereby adjusting the opening of the narrow passage 411. The other components are similar to those in the embodiment of Figure 19.

WHAT WE CLAIM 1S:- I. A control valve comprising: a body provided with two ports serving as an inlet and an outlet for a fluid; a fluid passage provided in said body for interconnecting said two ports; a movable valve member positioned in said fluid passage adjacent to a valve seat, the valve member being arranged so that a primary fluid pressure at the inlet tends to displace the valve member away from the valve seat, and the valve member and its degree of movement being such that at one extreme of its movement it co-operates with the valve seat to provide a flow restriction for fluid in said fluid passage, and at the other extreme of its movement it is displaced away from the valve seat so as to provide substantiallv no restriction to the flow of fluid in the fluid passage;; resilient means acting on said valve member tending to displace said valve member towards said valve seat; and a piston responsive to a secondary fluid pressure for displacing the valve member away from said valve seat against the action of said resilient means, the arrangement being such that a secondary fluid pressure lower than the inlet pressure will suffice to oppose the action of said resilient means.
2. A control valve as claimed in claim 1, wherein at said one extreme of its movement the valve member remains clear of the valve seat, the clearance between the valve member and the valve seat providing said flow restriction.
3. A control valve as claimed in claim 1, wherein the valve member is provided with a bypass bore and wherein at said one extreme of its movement, the valve member abuts the valve seat, the said bypass bore providing said flow restriction.
4. A control valve as claimed in claim 1, 2 or 3, and further including an adjustable member which limits the travel of the valve member.
5. A control valve as claimed in claim 1, 2, 3 or 4, wherein the piston is a pilot piston which divides a chamber within the valve into two parts, one part being in communication with a pilot port, the arrangement being

such that, in use, when fluid under pressure is supplied to said pilot port the fluid pressure acting on the piston forces the piston to force the valve member away from said valve seat.
6. A control valve as claimed in any preceding claim wherein said resilient means is a compression spring.
7. A control valve as claimed in claim 2 or 3 wherein the piston is integral with said valve member.
8. A control valve as claimed in claim 7, wherein the valve is mounted in the housing of a pneumatic actuator.
9. A control valve as claimed in any preceding claim wherein said valve also incorporates a throttle valve disposed in said fluid passage.
10. A control valve substantially as hereinbefore described with reference to and as shown in Figures 2 and 3.
II. A control valve substantially as hereinbefore described with reference to and as shown in Figure 4.
12. A control valve substantially as hereinbefore described with reference to and as shown in Figure 5.
13. A control valve substantially as hereinbefore described with reference to and as shown in Figure 8.
14. A control valve substantially as hereinbefore described with reference to and as shown in Figure 13.
15. A control valve substantially as hereinbefore described with reference to and as shown in Figure 19.
16. A control valve substantially as hereinbefore described with reference to and as shown in Figure 20.
17. A fluid circuit including a control valve substantially as hereinbefore described with reference to or as shown in any one of Figures 2, 4, 5, 8, 13, 19 and 20 of the accompanying drawings.
18. A fluid circuit comprising an actuator, a flow direction changeover valve, and a control valve sub-substantially as hereinbefore described with reference to or as shown in any of Figures 2 to 5, 7 to 13, and 17 to 20 of the accompanying drawings.