GB2041496A - Excess pressure valve assembly for hydraulic circuits - Google Patents

Abstract

The assembly comprises a main pressure release valve having a closure 2 and an associated seat 6 located in a chamber 4 between hydraulic circuit connection 5 and return pipe connection 9, and an auxiliary pressure release valve 24 in communication with the chamber 4 via flow paths defined by passages 13,14 in, and by the clearance around, the closure 2. A valve 17,19 gradually closes onto seat 34 to close the flow path 13,14 when normal operating pressure prevails in the circuit. Progressive increase in the circuit pressure above the limit value is released by the auxiliary valve 27. However, severe excess pressure is released by opening of the closure 2. The valve 24 comprises a hollow sliding needle enclosed at one end by a flexible member 27 located in pressurised chamber 28. <IMAGE>

Description

SPECIFICATION Excess pressure valve for hydraulic circuits This invention relates to an excess pressure valve for hydraulic circuits.

In certain hydraulic circuits, it is known that it is necessary to provide an excess pressure valve which opens as soon as the pressure in the circuit exceeds a value which is considered dangerous.

Excess pressure valves are known in which the pressure of the hydraulic circuit is applied by means of a hollow needle inside a flexible gasket in the shape of a glove finger, this gasket being compressed against the needle by means of a tight cushion filled with a gas under pressure. These valves are generally satisfactory, but they are unable to allow the passage of a high rate of flow of fluid under pressure.

Valves which can be used for allowing the passage of high rates of flow of fluid comprises a clack valve in which a resilient member pushes back against its seat. Thus, the least escaping excess pressure causes a displacement of the clack valve and a considerable leakage of fluid.

An object of the invention is to provide an excess pressure valve capable of construction to obviate or at least mitigate the aforementioned drawbacks, i.e. which is capable of dealing with a brief excess pressure without allowing an untimely leakage, but which is able to allow the passage of a high rate of flow of fluid when this is necessary.

According to the invention an excess pressure valve comprises a clack valve having a front face located in an annular chamber connected to a pressurised fluid circuit and defined between a bore in which the clack valve slides and a seat which the front end of the clack valve is able to close, a pipe for returning the fluid to the reservoir opening in front of the seat, a rear face of the clack valve being located in a rear chamber and being subject to action of a return spring which tends to push the clack valve forwards, the rear chamber being connected to the annular chamber through the intermediary of a passage provided in the clack valve, said passage being able to be closed by a slide valve which slides axially in the clack valve, and said rear chamber being also connected to an inlet aperture of an auxiliary excess pressure valve in which the pressure is applied inside the conduit of a hollow needle opening into a flexible gasket in the shape of a glove finger, the face of this gasket which is not in contact with the hollow needle being compressed by a cushion of pressurised gas.

The passage provided in the clack valve for connecting the rear chamber to the annular chamber valve can comprise a hole and an axial bore of the clack valve which is constantly closed in front of the clack valve by a cylindrical part of the slide valve. The hole extends between the axial bore and the front face of the clack valve. The clack valve can comprise a rear part which is able to move forwards under the effect of the pressure prevailing in the rear chamber to close the axial bore clack valve.

The clack valve can have a return spring which is compressed between an annular rear face of said clack valve and an annular shoulder provided at a rear and of the slide valve.

According to an additional feature of the invention, the annular chamber and the rear chamber of the clack valve are also connected to each other by the clearance which exists between the clack valve and the bore in which the clack valve slides.

The needle and the flexible gasket of the auxiliary excess pressure valve can slide in one piece in the manner of a piston inside the auxiliary excess pressure valve in order to compress the cushion of gas, this sliding movement allowing a displacement of the clack valve rearwards in the event of sudden excess pressure in the fluid circuit.

The longitudinal axes of the auxiliary excess pressure valve and the clack valve can be colinear. An inlet aperture of the auxiliary excess pressure valve can open in to the interior of the rear chamber through a wall against a rear face of the slide valve normally presses under the action of the return spring, when said slide valve is inoperative. The rear face of the slide valve has at least one groove allowing passage of fluid between the rear chamber and the inlet aperture of the auxiliary excess pressure valve when the slide valve is in the inoperative position.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section of an excess pressure valve formed according to the invention, and Figures 2 and 3 are also longitudinal sections of this valve, illustrating its operation.

Fig. 1 shows an excess pressure valve according to the invention. This valve comprises a main body 1 enclosing a clack valve 2, whereof the front annular face 3 is located in an annular chamber 4 connected to the pressurised fluid circuit 5. The annular chamber 4 is defined in the body 1 between a seat which the front frustonical end 7 of the clack valve 2 is able to close and a bore 8 in vw ch the clack valve 2 slides with clearance. The pipe 9 which extends in front of the seat 6 in the body 1 is a hydraulic outlet pipe or pipe for returning the fluid to the reservoir. Tha rear annular face 10 of the clack valve 2 is located in a rear chamber 11 of the body 1.

The rear chamber 11 is defined, in the rear part of the bore 8, by a plug 1 2 attached to the body 1.

The annular chamber 4 is connected to the rear chamber 11, in the body 1, on the onehand through the intermediary of the clearance which exists between the bore 8 and the corresponding cylindrical surface of the clack valve 2 and on the other-hand through the intermediary of a passage provided in the clack valve 2 itself. This passage comprises an axial bore 1 3 of the clack valve 2 and a hole 14 which extends obliquely between the front annular face 3 and this bore 1 3. The bore 13, which extends as far as the rear chamber 11, is extended forward by an axial bore 1 3a of smaller diameter.The bore 1 3a which opens into the pipe 9, is constantly closed by the front bearing surface 1 5 of a slide valve 1 6 mounted to slide axially in the clack valve 2.

The slide valve 1 6 also comprises a bearing surface 1 7 which is able to engage in the bore 13, closing off the latter when this slide valve moves forwards and which a cylindrical surface of small diameter 18 separates from the bearing surface 1 5. At its rear end, the slide valve 1 6 comprises an annular shoulder 1 9 and a return spring 20 is compressed between the rear annular face 10 of the clack valve 2 and this annular shoulder 1 9. The spring 20 is advantageously constituted by a stack of frustoconical spring washers. A diametral groove 21 cut in the rear transverse face 22 of the slide valve 16 allows the passage of fluid between the rear chamber 11 and an axial orifice 23 in the plug 12.

The aperture 23 constitutes the inlet aperture of an auxiliary excess pressure valve 24 fixed to the plug 1 2. The latter is a conventional excess pressure valve in which the pressure is applied in the conduit 25 of a hollow needle 26 opening into the inside of a flexible gasket 27 in the shape of a glove finger. The face of the gasket 27 which is not in contact with the hollow needle 26 defines a cushion of gas 28 at the blind end of the body 29 of the valve 24. The cushion of gas 28 may be pressurised through the intermediary of a filling aperture 30 in the body 29. A bush 31, which is fitted around the needle 26 in front of the flexible gasket 27, comprises radial holes 32 through which tfre fluid may escape to the outside, the holes 32 being located in facing relationship to holes 33 in the body 29.In fact, in the case of an excess pressure, a controlled leakage of fluid occurs between the outer surface of the hollow needle and the flexible gasket 27.

When the valve 24 is inoperative, the front edge of the flexible gasket 27 is kept in abutment against the bush 31 under the effect of the pressure of the cushion of gas 28. If an abnormally high excess pressure occurs at the inlet 23, the arrangement comprising the hollow needle 26, the flexible gasket 27 and the bush 31 may slide in one piece in the body 29, in the manner of a piston, in the direction of the rear of the body 29.

The operation is as follows: If a hydraulic operating pressure, which is less than the limit value allowed, is established suddenly in the hydraulic circuit 5, this pressure is immediately applied in the rear chamber 11 of the valve. In fact, the slide valve 16, which has not had time to leave its inoperative position (Fig. 1), allows fluid to pass through the bore 13, the annular chamber 4 and the rear chamber 11 thus being connected to each other by means of a passage of considerable cross-section. Due to the construction, when the chambers 4 and 11 are at the same pressure, the axial thrust produced by the pressure of the chamber 11 on the clack valve 2 is greater than the axial thrust produced by the pressure of the chamber 4 on this same clack valve, but in the opposite direction.Thus, in the aforementioned case, the sole effect of an operating pressure being established suddenly is to keep the clack valve 2 pressed even more tightly against the seat 6, the pressure forces cooperating with the spring 20 to this end.

When the operating pressure is applied permanently, the pressure forces prevail over the spring 20, thus pushing the slide valve 1 6 progressively forwards. As it moves forwards, the slide valve 1 6 closes the bore 1 3 with its bearing surface 1 7 (Fig. 2) and the annular shoulder 1 9 finally arrives in abutment against a rear lip 34 of the clack valve 2.

In this position, the rear chamber 11 continues to be connected to the annular chamber 4 through the intermediary of the passage of small cross-section constituted by the clearance provided between the clack valve 2 and the bore 8 in the body 1.

If the hydraulic pressure rises above the limit value allowed, the auxiliary excess pressure valve 24 is thus able to allow a controlled leakage of fluid to escape in order to bring about a return of the pressure to the normal value. This allows slow and progessive regulation of the pressure, so long as the excess pressures are themselves progressive.

In the case of severe excess pressure, the hydraulic shock wave is restricted between the clack valve 2 and the bore 8, so that the excess pressure of the circuit is unable to reach the rear chamber 11. The excess pressure thus acts solely on the clack valve 2 in the region of the annular chamber 4. The clack valve 2 moves immediately rearwards thus moving away from the seat 6 (Fig. 3), which is made possible owing to a sliding movement of the hollow needle 26, of the flexible gasket 27 and of the bush 31 in the body 29 of the valve 24. A high rate of flow of fluid may thus return to the reservoir through the intermediary of the pipe 9. As soon as the pressure drops, the cushion of gas 28 pushes the flexible gasket 27 forwards, whilst the clack valve 2 returns to the seat 6.

The valve according to the invention has the following advantages in particular: -When the operating pressure is established rapidly in the circuit, for example at the time of sudden starting, one eliminates any displacement of the main valve and consequently any inopportune leakage of hydraulic fluid.

-In normal operation, the valve ensures slow and progessive operation, thus compensating for progressive excess pressure by controlled leakages.

-In the case of severe excess pressure, of the "water hammering" type, the valve quickly allows leakage with a high rate flow, thus limiting the rise in pressure.

The valve can be used for any system for protecting a high pressure hydraulic circuit. In particular, it can be used for protecting the props of rams for support timbering in mines.

Thus, the clack valve 2 operates only exceptionally, in the case of a movement in the roof of the mine, which prevents twisting of the props or breakage of the pins acting as safety cotter pins. Nominal calibration may be 500 bars for example. In case of "water hammer ing", the valve prevents the pressure from exceeding 700 bars.

Claims (9)

1. An excess pressure valve comprising a clack valve having a front face located in an annular chamber connected to a pressurised fluid circuit and defined between a bore in which the clack valve slides and a seat which the front end of the clack valve is able to close, a pipe for returning the fluid to the reservoir opening in front of the seat, a rear face of the clack valve being located in a rear chamber and being subject to action of a return spring which tends to push the clack valve forwards, the rear chamber being connected to the annular chamber through the intermediary of a passage provided in the clack valve, said passage being able to be closed by a slide valve which slides axially in the clack valve, and said rear chamber being also connected to an inlet aperture of an auxiliary excess pressure valve in which the pressure is applied inside the conduit of a hollow needle opening into a flexible gasket in the shape of a glove finger, the face of this gasket which is not in contact with the hollow needle being compressed by a cushion of pressurised gas.

2. A valve as claimed in claim 1, in which the passage provided in the clack valve for connecting the rear chamber to the annular chamber comprises a hole and an axial bore of the clack valve which is constantly closed in front of the clack valve by a cylindrical part of the slide valve, said hole extending between said axial bore and the front face of the clack valve, and the clack valve comprises a rear part which is able to move forwards under the effect of the pressure prevailing in the rear chamber in order to close said axial bore.

3. A valve as claimed in claim 1 or claim 2, in which a return spring of the clack valve is compressed between an annular rear face of said clack valve and an annular shoulder provided at a rear end of the slide valve.

4. A valve as claimed in claim 3, in which the force of the return spring is chosen so that, when the hydraulic operating pressure of the hydraulic circuit is established in the rear chamber, the pressure forces acting on the slide valve prevail over the return spring in order to push the slide valve forwards.

5. A valve as claimed in any preceding claim, so designed that when the annular chamber and the rear chamber are at the same pressure, the axial thrust produced by the pressure in the rear chamber on the clack valve is greater than the axial thrust in the opposite direction on said clack valve produced by the pressure in the annular chamber direction.

6. A valve as claimed in any preceding claim, in which the annular chamber and the rear chamber are also connected to each other by means of a clearance provided between an outer cylindrical surface of the clack valve and a bore in which the clack valve slides.

7. A valve as claimed in any preceding claim, in which the auxiliary excess pressure valve comprises a bush which is mounted at the front of the flexible gasket around the hollow needle, the arrangement comprising said bush, the hollow needle and the flexible gasket being able to slide in one piece, in the manner of a piston, inside a body of the auxiliary excess pressure valve in order to compress the cushion of gas, this sliding movement allowing the displacement of the clack valve rearwards in the event of sudden excess pressure in the fluid circuit.

8. A valve as claimed in any preceding claim, in which the longitudinal axes of the auxiliary excess pressure valve and the clack valve are co-linear, an inlet aperture of the auxiliary excess pressure valve opens into the interior of the rear chamber through a wall against which a rear face of the slide valve normally presses under the action of a/the return spring, and the rear face of the slide valve comprising at least one groove allowing passage of hydraulic fluid between said rear chamber and said inlet aperture when the slide valve is in its inoperative position.

9. An excess pressure valve substantially as hereinbefore described with reference to the accompanying drawings.