GB2080498A

GB2080498A - Improvements in or relating to hydraulic valves

Info

Publication number: GB2080498A
Application number: GB8118615A
Authority: GB
Original assignee: AEI
Current assignee: AEI
Priority date: 1980-07-23
Filing date: 1981-06-17
Publication date: 1982-02-03
Also published as: GB2080498B

Abstract

According to this invention a control valve for a hydraulic actuator incorporates a piston (10) on which are mounted spring loaded inlet and outlet poppets (1, 2) which cooperate with apertures in a casing (C) to form respective inlet and outlet valves controlling the flow of fluid to and from the actuator respectively, said poppets being mounted for independent movement, and movement of both poppets against said spring loading being controlled by hydraulic pressure in a common control chamber (7). <IMAGE>

Description

SPECIFICATION Improvements in or relating to hydraulic valves This invention relates to control valves for hydraulic actuators, particuiarly for use in high voltage electrical circuit interrupters.

It is an object of this invention to provide a control valve for a hydraulic actuator which can safely withstand loss and restoration of hydraulic pressure without causing unwanted actuation.

Further objects of the invention are that hydraulic pressure transients in the actuator are substantially reduced and oil consumption by the control valve is minimised.

According to one aspect of the present invention a hydraulic control valve for controlling the operation of a hydraulic actuator incorporates a piston on which are mounted spring loaded inlet and outlet poppets which co-operate with apertures communicating with the actuator, and are mounted for independent movement, the inlet poppet being movable to regulate or prevent supply of hydraulic fluid to the actuator and the outlet poppet being movable to regulate or prevent discharge of hydraulic fluid from the actuator, movement of both poppets against said spring loading being controlled by hydraulic pressure in a common control chamber.

The pressure in the control chamber may be controlled by a servo valve or by any other convenient means.

A control valve in accordance with the invention may be arranged so that both the inlet and outlet poppets cannot be in the open position simultaneously. This is desirable since direct loss of hydraulic fluid through the control valve is prevented.

According therefore to another aspect of the invention a hydraulic control valve incorporates a valve chamber arranged to be connected in use to a hydraulic actuator, an inlet valve poppet arranged to control the supply of pressurised hydraulic fluid into the valve chamber, and thence to the actuator, an outlet valve poppet for controlling the return of hydraulic fluid from the valve chamber, and hence from the actuator, the valve poppets being spring loaded into the closed position and being independently openable by variation of fluid pressure on the operative faces of respective driving pistons in a common control chamber, the relative areas of the piston faces and the spring loading being such that the poppets can both be closed but cannot both be open simultaneously.

The inlet and outlet poppets are preferably arranged so that positive hydraulic pressure in the control chamber acting on the operative faces of the driving pistons in said control chamber urges the inlet poppet to open and urges the outlet poppet to close.

Conveniently the outlet poppet and the driving piston therefor are slidably mounted on the inlet poppet driving piston.

The spring biasing of the inlet and outlet poppets is preferably such as to hold both poppets closed when the hydraulic pressure in the control chamber is zero. A loss of pressure may occur, for example, during maintenance of the system and it is an important feature of the invention that unwanted and possibly dangerous actuation does not occur when the pressure is restored.

The spring biasing of the outlet poppet is preferably such as to require a negative pressure in the control chamber to cause the poppet to open.

Pressure transients are reduced in preferred embodiments of the invention by reducing the initial opening speed of the inlet poppet. Pressure transients are preferably further reduced by provision of an obstruction on the inlet poppet which restricts the passage of hydraulic fluid through the respective inlet during the initial opening movement of the inlet poppet. The initial opening speed of the inlet poppet may be reduced in two ways. Admission of oil to the inlet poppet piston may be restricted during its initial opening movement. Alternatively the inlet poppet may drive a ported piston which impedes the initial movement of the poppet. The ported piston is preferably arranged to move independently of the inlet poppet so that the closing movement of the latter is not impeded.

The invention may be better appreciated from the following description, by way of an example in accordance with the invention, of two control valves for hydraulic actuators for electric circuit breakers.

Figure 1 shows a sectional view of a control valve.

Figure 2 shows a sectional view of part of a second control valve.

The control valve shown in Figure 1 comprises an inlet poppet 1 and an outlet poppet 2 within a common casing C (shown only in part). The inlet poppet 1 serves to regulate or prevent the admission of high pressure hydraulic fluid from an accumulator through a port 3 in the housing wall into the main valve chamber A for delivery from there, through a further port 4, to an actuator (not shown). The outlet poppet 2 controls the return flow-of fluid from the actuator to a reservoir (not shown) through another port 5.

The inlet poppet 1 and outlet poppet 2 are slidably mounted on a piston 10 which itself is free to slide within the control valve casing C.

Three guides 14 (only one of which is shown) are provided to ensure correct alignment of the inlet poppet which is urged to the closed position by a spring 1 8. The end surface 11 of the piston 10 remote from the inlet poppet 1 and an adjacent surface 1 6 of the outlet poppet 2, both form pistons against which hydraulic pressure in a control chamber 7 may act to actuate the inlet and outlet poppets. A port 1 9 from the exterior of the piston 10 to the interior of the poppet 1 permits free sliding movement of the poppet on the piston.

The breaker is closed by opening the inlet poppet 1 to admit pressurised hydraulic fluid from an accumulator through the port 3 and delivering it through the port 4 to the circuit breaker actuator. To open the breaker the inlet poppet 1 is closed and the outlet poppet 2 is opened to permit hydraulic fluid to be discharged from the actuator into the valve chamber A and then into the reservoir through the port 5. These poppet movements are brought about by admitting hydraulic fluid through a port 6 into the control chamber 7 to open the inlet poppet 1, and by exhausting the chamber 7 to close the poppet 1 and open the poppet 2. The supply of fluid to the port 6 is by a servo valve (not shown) driven by trip and close solenoid pilot valves according to normal circuit breaker practice.

When for example for maintenance purposes the oil pressure in the system is reduced to zero, it is important that the pressure can safely be subsequently restored without moving the actuator piston. With the arrangement shown both poppets 1 and 2 are closed at low hydraulic pressures so that the breaker can not be actuated simply by the increase in the hydraulic pressure.

Furthermore with a servo valve which is controlled to be in the state corresponding to the state of the breaker, i.e. open when the breaker is open and closed when the breaker is closed, and which will not reset automatically, as pressure is restored, poppet 1 or 2 moves to the appropriate position.

The outlet poppet 2 normally closes under the action of a spring 8 and is opened when the pressure in the control chamber 7 is at an adequate low value. The piston sizes are also such that the force due to fluid pressure urging the outlet poppet 2 closed is always greater than the force due to fluid pressure acting on the piston 10 and urging the inlet poppet 1 to open. Hence the poppet 2 always closes before the poppet 1 opens and poppet 1 always closes before poppet 2 opens. This ensures that there is never an overlap in poppet opening and that there can be no direct loss of oil through the control valve.

The initial opening speed of the inlet poppet 1 is reduced to reduce the pressure transients consequent upon the admission of high pressure fluid. The poppet is provided with an obstruction 9 which reduces the fluid flow during the initial opening movement.

The opening speed is also controlled. Hydraulic fluid is admitted from the chamber 7 to the piston 10 through an orifice 1 7 which is initially obstructed but opens fully after the piston has moved a predetermined distance. By this means the full opening speed is not attained until the valve has opened somewhat. Similar damping occurs during the last stages of closure of the poppet 1.

The Figure 2 shows an alternative method of fluid damping. The poppet 1 slidingly supports a ported piston 12 which is iocated between the spring 18 and the poppet 1 and acts as a fluid damper during the initial opening movement of the poppet. After a short travel the ports 1 3 are by-passed so that the damping restriction is removed and the valve can travel at full speed. The piston 12 has three radially projecting axiallyextending projections 15 (only one of which is shown) which are spaced equilaterally about the piston 12 and slide in guide slots in the valve casing, thereby ensuring that the piston 1 2 moves in the correct axial direction. Since it is slidingly supported on the poppet 1 this allows the poppet to move rapidly independently of the piston 12 when the poppet closes.

Claims

1. A hydraulic control valve for controlling the operation of a hydraulic actuator incorporating a piston on which are mounted spring loaded inlet and outlet poppets which co-operate with apertures communicating with the actuator, and are mounted for independent movement, the inlet poppet being movable to regulate or prevent supply of hydraulic fluid to the actuator and the outlet poppet being movable to regulate or prevent discharge of hydraulic fluid from the actuator, movement of both poppets against said spring loading being controlled by hydraulic pressure in a common control chamber.

2. A hydraulic control valve incorporating a valve chamber arranged to be connected in use to a hydraulic actuator, an inlet valve poppet arranged to control the supply of pressurised hydraulic fluid into the valve chamber, and thence to the actuator, an outlet valve poppet for controlling the return of hydraulic fluid from the valve chamber, and hence from the actuator, the valve poppets being spring loaded into the closed position and being independently openable by variation of fluid pressure on the operative faces of respective driving pistons in a common control chamber, the relative areas of the piston faces and the spring loading being such that the poppets can both be closed but cannot both be open simultaneously.

3. A control valve according to Claim 2 wherein positive hydraulic pressure acting on the operative faces of the pistons in the control chamber urges the inlet poppet to open and the outlet poppet to close.

4. A control valve according to Claim 3 wherein the outlet poppet and the driving piston therefor are slidably mounted on the inlet poppet driving piston.

5. A control valve according to any preceding Claim wherein the spring biasing of the inlet and outlet poppets is such as to hold both poppets in the closed position when the hydraulic pressure in the control chamber is zero.

6. A control valve according to Claim 4 wherein the spring biasing of the outlet poppet is such as to require a negative pressure in the control chamber to cause the poppet to open.

7. A control valve according to any preceding Claim in which the inlet poppet opens outwards against the supply of hydraulic fluid

8. A control valve according to any preceding Claim in which the inlet poppet is provided with a stepped portion adjacent to its seating surface of such dimensions as to significantly increase the dynamic fluid resistance to the opening of said poppet during the early part of its travel.

9. A control valve according to any preceding Claim in which part of that surface of the inlet poppet piston which is acted on by the fluid in the hydraulic control chamber and lies transverse to the direction of travel of the inlet poppet is in restricted communication with said fluid when said poppet is in its closed position.

10. A hydraulic control valve according to any preceding Claim in which a ported piston is slidably mounted on that part of the inlet poppet which is acted on by the hydraulic supply, the inlet poppet forming a stop against which the ported piston is urged by spring means tending to close the inlet poppet, the ported piston slidingly registering with an inwardly stepped portion of the valve casing when the inlet poppet is in its closed position.

11. A control valve substantially as described hereinabove with reference to Figure 1.

12. A control valve substantially as described hereinabove with reference to Figure 2.

13. A hydraulically actuated electrical circuit interrupter incorporating a control valve according to any preceding Claim.

14. A hydraulically actuated electrical circuit interrupter incorporating a hydraulic control valve according to any of Claims 1 to 12, and which is closed by opening the inlet poppet and opened by opening the outlet poppet.