GB2131207A - A control valve - Google Patents

Abstract

The valve comprises inlet and outlet passages 11a, 11b, a pressure reducing orifice 12 between the inlet and outlet, a flow control member 2 operable in response to the difference in fluid pressures upstream and downstream of the orifice and a pressure relief valve member 17. The relief valve operates in response to pressure downstream of the orifice 1A, so that when the downstream pressure exceeds a particular value the pressure relief member operates to allow the flow control member 2 to prevent or reduce the flow of fluid to the outlet. The orifice may be provided integral with the valve, Figure 2, (not shown). <IMAGE>

Description

SPECIFICATION A control valve This invention relates to a control valve.

Hydraulic fluid is conventionally supplied from a source at a high pressure and flow rate, eg. a pressure of about 2,500 psi and a flow rate of about 60 gals/min. This pressure and flow rate are however often much higher than are required to drive certain hydraulic appliances, such as hand tools. It is therefore, necessary to incorporate control valve means into the hydraulic circuit which limit both the pressure and the flow rate of the fluid to be supplied to such an appliance. Previously, separate pressure control and flow control valves have been required.

This is disadvantageous as separate assembly of the respective valves into a hydraulic circuit is neces sary.An object of the present invention is to provide an improved control valve which mitigates the foregoing disadvantage.

According to the invention there is provided a control valve comprising an inlet and an outlet for fluid, pressure reducing means between the inlet and outlet, flow control means operable in response to the difference in fluid pressures upstream and downstream of the pressure reducing means, and pressure relief means operable in response to pressure downstream of the pressure reducing means so that when the pressure downstream of the pressure reducing means exceeds a given value the pressure relief means operates to allow the flow control to reduce the flow of fluid.

Preferably the pressure reducing means the flow control means and the pressure relief means are assembled as a single unit housed within a bore formed in a body. Such an arrangement makes the valve particularly easy to manufacture because the assembly of the working parts can be carried out virtually completely before location in the valve body.

The flow control means may be a cylindrical member mounted for axial sliding in a sleeve which has an inlet port, said cylindrial member being arranged to control flow of fluid through the inlet port.

The cylindrical member may comprise a spool member or a hollow annular member. Preferably, the fluid pressure upstream of the pressure reducing means is arranged to urge the cylindrical member in one direction along the sleeve to reduce fluid flow through the port and the fluid pressure downstream of the pressure reducing means is arranged to urge the cylindrical member in the opposite direction along the sleeve. In such a case, movement of the cylindrical member in said one direction may load resilient means, eg. a compression spring or other resilient member.

The pressure relief means may allow fluid to flow therethrough faster than it can be replenished from the inlet to enable the flow control means to prevent or reduce the flow of fluid to the outlet.

The control means may comprise an orifice through which fluid flows to the outlet. In such a case, the orifice may be defined by a fixed member defining a bore and an adjustable member which is movable towards or away from the bore whereby the orifice is defined between the bore and an adjacent peripheral portion of the adjustable member. Alternatively the orifice may comprise a constriction in an outlet passage formed in said body.

Control valves in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic longitudinal section through one form of valve in accordance with the invention, and Figure2 is a longitudinal section through an alternative valve in accordance with the invention.

In Figure 1 the valve comprises a sleeve 1 and a valve member in the form of a spool 2 of circular cross-section. The spool is slidable within a cylindrical cavity in the sleeve against the action of a retaining spring 10. The sleeve has inlet ports 3 and outlet ports 4for hydraulic fluid.

The spool has a central portion 5 of reduced diameter and two end portions 6 which fit slidably and substantially sealingly within the sleeve 1. The space around the central portion provides a pathway 7 for fluid between the inlet and outlet ports 3,4. The spool 2 is displaceable relative to the sleeve 1 in such a way that the inlet ports 3 can be partially or completely covered by the end portion 6 of the spool.

The sleeve 1 is positioned in a bore 1a formed in a body 1b and is held in place by a housing 15 which screws into the body. The housing 15 is secured to the right-hand end of the sleeve by an in-turned setion 1 spa. A chamber 8 is defined between the left-hand end of the spool 2 and the bore 1a and a further chamber 9 is defined between the right-hand end of the spool and the interior of housing 15. A helical coil spring 10 is arranged in the chamber 9 and biases the spool normally against an internal circlip C on the sleeve 1.

The ports 3 communicate with an inlet passage 1 in the body lb and the port 4 communicates with an outlet passage 11b in the body lb. The outlet pasage 1 1b is provided with an internal constriction in the form of an orifice 12. Downstream of this orifice the passage 1 1b is, in use, connected to a hydraulic actuator such as the motor of an applicance to be driven from the hydraulic supply. On the upstream side of the orifice 12 is provided a passage 13 communcating with the chamber 8, and on the downstream side a further passage 14 communicating with the chamber 9.Thus, the pressures immediately upstream and downstream of the orifice are conveyed to the chambers 8 and 9 respectively, and the pressure difference controls the position of the spool 2 within the sleeve 1, in conjunction with the spring 10.

The chamber 9, is in communication with a fluid discharge passage 16 in the body through a pressure relief valve 17. This pressure relief valve comprises a dart-shaped valve member 18 which can seat within a passage 19 of a cross-section d1.

The passage 14 is connected to the chamber 9 through a portion of reduced cross-section d2, where d1 > d2. In use, the discharge passage 16 is connected to a hydraulic fluid reservoir which is at atmospheric pressure. The pressure relief valve 17 is urged normally into the closed position by a spring 20 which reacts against a retaining screw 21. The latter screw could, if desired, take the form of a set screw by which the loading on the spring 20 could be varied.

In use the inlet passage 11 a is connected to a source of hydraulic fluid under pressure and the outlet passage 1 1b is connected to the actuator. The spring 20 is set so that the relief valve 17 will open when pressure downstream of the orifice 12 reaches a given value. With fluid passing to the actuator through the valve, the pressure in chamber 8 tends to urge the spool to the right whilst the relatively smaller pressure in chamber 9 together with the bias of spring 10 tends to urge the spool to the left and a balance will be achieved with the spool controlling the opening of inlet port 3. If, say, the actuator stalls so that fluid flow decreases, there will be a build up of pressure downstream of the orifice which will increase the pressure in chamber 9.If pressure rises sufficiently to open the relief valve 17, fluid in chamber 9 will escape past the valve member 18 so that pressure downstream of the orifice cannot rise further. As dl > d2, fluid cannot enter chamber 9 from passage 14fasterthan it can leave through passage 19 and pressure in chamber 8 will cause the spool to move to the right against the bias of spring 10 and reduce the flow through port 9 sufficiently to maintain the pressure downstream of the orifice to that determined by the relief valve. As soon as the downstream pressure falls again, spring 10 urges the spool to the left to allow fluid to move once more through the valve to the actuator.

In Figure 2 the valve comprises a sleeve 30 having an annular part 32 axially fast with its left-hand end, as viewed in the drawing, and a series of inlet ports 33. The right-hand end of the sleeve is screwed to the exterior of a coaxial tubular guide member 34 which is screwed to the interior of a coaxial housing 35. The sleeve 30 houses a coaxial tubular control member 36 which is axially slidable within the sleeve and in substantially sealing engagement therewith.

The control member is also slidably mounted in an elongate tube 37 which extends coaxially and sea linglythrough the guide member 34.

A compression spring S extends between the control member 36 and a guide member 34 and a chamber 60 is defined between the latter members.

The elongate tube 37 has a frusto-conical left-hand end 31 which co-operates with the part 32 as described below. The right-hand end of the tube 37 is axially fast with an adjustment sleeve 38 which is screwed to the interior of the housing 35. The right-hand end of the adjustment sleeve has surfaces 39, eg hexagon flats, for receiving torque applying means and carries a locking nut 40 co-operable with the right-hand end of the housing 35.

By slackening locking nut40and rotating the adjustment sleeve 38 the tube 37 moves axially whereby the frusto-conical end 31 moves towards or away from the part 32 to enable an annular orifice A, of desired area to be defined therebetween.

The adjustment sleeve 38 houses a dart-shaped relief valve member 41 which is urged against the right-hand end of the tube 37 by one end of a spring 42 to close the bore (indicated at 41 a) of the tube.

The opposite end ofthe spring 42 abuts an adjustabie stop 43 which sealingly engages the sleeve 38.

The spring 42 normally urges the stop 43 against an adjustment screw 44 which can be rotated by suitable means, to adjust the loading on the spring 42.

The control member 36 is formed with a plurality of ports 45 which communicate with a peripheral groove 46 in the control member. The housing 35 is formed with a drain bore 47. The sleeve 38 is formed with transverse ports 48 and the tube 37 is formed with a transverse bore 49. The left-hand end of the bore 41a of tu be 37 terminates at a reduced diameter section 41b.

The assembled components are located in a valve body 50. The body 50 is formed with a bore 52 which comprises a series of counterbores 53, 54 and 55.

The counterbore 53 is screw-threaded and receives a screw-threaded section 156 of the housing 35.

The housing 35 is formed with surfaces 157 such as hexagon flats for receiving torque applying means. The counterbores 54 and 55 are sealingly engaged by sealing portions 56 and 57 respectively on the sleeve 30. The body 50 is formed with an inlet passage 58 and a drainage passage 59.

In use, the inlet passage 58 is connected to a source of hydraulic fluid under pressure, the counterbore 55 is connected to the actuator such as hydraulic tool and the drainage passage 59 is connected to a fluid reservoir (Not shown) at atmospheric pressure. The orifice A is set as required. Fluid from the inlet passages passes through the ports 33 and 45, through the orifice A and out of the left-hand end of the sleeve 30, which constitutes an outlet, and into counterbore 55.

Flow through the orifice causes a pressure difference to occur between the flow upstream and downstream of the orifice. The lower downstream pressure is conveyed to chamber 60 through bores 41 h, 41 a and 49. The higher upstream pressure tends to urge the control member to the right against the bias of spring S and pressure in chamber 60 until the loads on the opposite ends of the control member are in the balance. Movement of the control member to the right reduces the flow of fluid from inlet passage 58 to the orifice A. If, say, the actuator stalls so that fluid flow decreases there will be a build up of pressure downstream of the orifice A, which will cause pressure in chamber 60 and hence in bore 41a to increase.

If pressure rises sufficiently to open the relief valve member 41, fluid in bore 41a will escape through ports 48, drainbore 47 and drainage passage 59, so that pressure downstream of the orifice A cannot rise further.

The pressure at which the relief valve member 41 is forced to open can be controlled by the loading on spring 42.

In view of the reduced diameter section 41b, the pressure in bore 41a will be less than that in bore 55.

The reduction in pressure in bore41a causes the pressure upstream of the orifice A to push the control member 36 to the right so as eventually to close the port 33 or permit only a samil amount of fluid to pass therethrough and out through bore 41a and drainage 59 so as to maintain the pressure in bore 55 to that determined by the relief valve member.

As soon as the pressure downstream of the orifice Afalls, the relief valve member 41 closes and pressure in the bore 41a and hence chamber 60 becomes substantially equal to that in bore 55.

The pressure immediately upstream of the orifice is also substantially equal to that downstream of the orifice and the spring S moves the control member 36 to the left to increase flow to the orifice to drive the actuator.

The invention allows both pressure and flow rate to be controlled by a single valve. Moreover, the valve can be assembled as a single unit and then introduced into a valve body having appropriate passages for the fluid. The Figure 2 embodiment is particularly advantageous as members defining the orifice A are housed within the sleeve 30 and the valve unit itself, rather than the body, defines passageways through which fluid is fed to control the axial position of the control member 36. The construction of the body 50 is thereby greatly simplified.

Claims (10)

1. A Control Valve Comprising an inlet and outletforfluid, pressure reducing means between the inlet and outlet, flow control means operable in response to the difference in fluid pressures upstream and downstream of the pressure reducing means, and pressure relief means operable in response to pressure downstream of the pressure reducing means so that when the pressure downstream of the pressure reducing means exceeds a given value the pressure relief means operates to allowthe flow control means to reduce the flow of fluid.

2. A control valve according to Claim 1, in which the pressure reducing means, the flow control means and the pressure relief means are assembled as a single unit housed within a bore formed in a body.

3. A control valve according to Claim 1 or 2, in which the flow control means is a cylindrical member mounted for axial sliding in a sleeve which has an inlet port, said cylindrical member being arranged to control flow of fluid through the inlet port.

4. A control valve according to Claim 3, in which the fluid pressure upstream of the pressure reducing means is arranged to urge the cylindrical member in one direction along the sleeve to reduce fluid flow through the port and the fluid pressure downstream of the pressure reducing means is arranged to urge the cylindrical member in the opposite direction along the sleeve.

5. A control valve according to Claim 4 in which movement of the cylindrical member in said one direction loads resilient means.

6. A control valve according to any preceeding claim in which the pressure relief means allows the fluid to flow therethrough faster than it can be replenished from the inlet to enable the flow control means to reduce the flow of fluid.

7. A control valve according to any preceeding claim in which the flow control means comprises an orifice through which fluid flows to the outlet.

8. A control valve according to Claim 7 in which the orifice is defined between a fixed member defining a bore and an adjustable member which is movable towards or away from the bore whereby the orifice is defined between the bore and an adjacent peripheral portion of the adjustable member.

9. A control valve according to Claim 7 when appendant to Claim 4 in which the adjustable member is an elongate tube through which fluid flows from a position downstream of the pressure reducing means to urge said cylinder in said opposite direction and through which fluid flows to said pressure relief means.

10. A control valve constructed and arranged substantially as described herein with reference to Figure 1 or Figure 2 of the accompanying drawings.