GB1566873A

GB1566873A - Relief valves

Info

Publication number: GB1566873A
Application number: GB3989176A
Authority: GB
Original assignee: Centre Stephanois de Recherches Mecaniques Hydromecanique et Frottement SA
Current assignee: Centre Stephanois de Recherches Mecaniques Hydromecanique et Frottement SA
Priority date: 1976-09-25
Filing date: 1976-09-25
Publication date: 1980-05-08

Description

(54) IMPROVEMENTS IN OR RELATING TO RELIEF VALVES (71) We, CENTRE STEPHENOIS DE RICHERCHES MECHANIQUE HYD ROMECHANIQUE ET FROTZTEMENT, a body corporate organised and existing under the laws of France, of Zone Industrielle Sud, Rue Beniot, Fourneyron Andreyièup Boutheon (Loire) France 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: The present invention is concerned with a relief valve for use in a hydraulic circuit.

Many kinds of relief valves for used in mine props especially are known. Such a valve is adapted to establish leakage from a fluid circuit where the fluid is compressed beyond a determined pressure limit.

uncertain known relief valves, the fluid pressure is applied so as to raise a valve member from its seat by acting against an opposing spring. In the absence of pressure, the 5 ring maintains the valve member very forcibly against its seat. This permanent contact ensures conservation of the surfaces. Moreover, the spring is always compressed and it happens frequently that the pressure limit or calibration of the valve varies according to the shelf life. Indeed when the fluid pressure is lower than this calibration the force of application of the valve member on its seat varies inversely to the fluid pressure such that if the calibration is not precise the opening of the valve is very progressive.

In other known relief valves, the valve member is urged against its seat by a reserve of compressed gas. There again the contiguous surfaces are constantly compressed, and one cannot control the calibration value which necessitates storage of a large number of valves of different kinds.

The present invention has for its object the obviating of these inconveniences by providing a valve in which the forces applied to the contacting surfaces at the edge of the seat remain practically nil when the fluid circuit is not under pressure. This valve has moreover a more precise calibration value which is controllable.

According to the invention there is provided a relief valve comprising a body in which a fluid-tight chamber is adapted to be put into communication with a pressurised fluid circuit, and a valve member within the chamber and resiliently urged against a seat to close the chamber, the seat being disposed on a barrel freely slidable in the body to take up a balanced condition between fluid pressure forces in the chamber, and, the force of a return spring, whereof one end abuts the barrel, an abutment fixed to the body being provided, so as to be contactable by the valve member when the latter is on its seat and moving with the barrel so that - if the fluid pressure in the chamber is nil the return spring is loaded only by the resilient pressure urging the valve member against its seat and is thus practically noncompressed, - if the fluid pressure remains lower than a predetermined calibration value for the valve, the valve member is applied against its seat by the fluid with a force proportional to this fluid pressure and the barrel slides to more or less compress the return spring, - if the pressure is above the predetermined calibration value of the valve, the barrel further compresses the return spring causing the valve member to contact the abutment whereby it is spaced from its seat.

Preferably, the body comprises a central bore, whereof one end is closed by a cap having an integral coaxial stem which extends into a central bore of the barrel, the cap being provided with an axial throughhole to permit the valve to be placed in communication with the pressurised fluid circuit and the chamber being within the barrel bore and being delimited by the end of the stem, a seal being provided between the cylindrical surface of the stem and the barrel, Preferably also, the chamber encloses a small helical spring constantly compressed between the valve member and the end of the stem to provide the resilient loading which urges the valve member against its seat, this small spring being much less powerful than the barrel return spring.

The valve member may be constituted by a ball and the seat is constituted by a frusto-conical bore in a disc carried by the barrel.

The valve member may be of frustoconical shape and the seat is constituted by the orifice of a hole in the barrel.

The valve member may have at its end a plane annular surface adapted to abut against the face of a circular boss constituting the seat.

The return spring of the barrel is preferably constituted by a helical spring, whereof one end abuts a shoulder of the body, at the end of the central bore, and whereof the other end abuts the slidable barrel.

Preferably, the other end of the central bore of the valve body is also closed by a cap in the centre of which is fixed a rod extending axially into the bore and adapted to engage with substantial play inside the seat on the sliding barrel, and whereof the free end constitutes the abutment for the valve member. This abutment can be plane, round, or any other appropriate form to suit the type of valve member.

This rod is preferably screw engaged in a bore of the cap, and it can be used to determine the calibration value of the valve by being screwed in one direction or the other, which varies the longitudinal position of its free end.

The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a sectional view of a relief valve according to the invention; Figures 2 and 3 are views of part of the valve of Figure 1 shown to an enlarged scale in closed and open position respectively; Figure 4 is a sectional view showing a modification, to an enlarged scale, of part of the valve shown in figure 1; Figure 5 is another sectional view showing a further modification, to an enlarged scale, of part of the valve shown in Figure 1; and Figure 6 is a diagram in the form of a graph showing the functioning of the relief valve.

As shown in Figure 1, the relief valve according to the invention comprises a body 1 with a central cylindrical bore 2 sealed at both ends by caps 3 and 4.

The cap 3 is fixed to the body 1 by means of screws (not shown) and it is attached to a screw-threaded nozzle 6 enabling the valve to be connected into a hydraulic circuit in a known manner. The cap 3 is integral with a coaxial stem 7 which extends into the bore 2 and which itself has an axial bore X.

A barrel 9 with an axial bore therethrough slides freely in the bore 2 and one of the ends of the barrel is recessed to accommodate a disc 10. A sealing ring 11 is compressed between the barrel 9 and the disc 10. The disc 10 has an axial frustoconical bore 12 therethrough which widens towards the interior of the barrel 9 and which forms the valve seat. The closure member of the valve is a ball 14. A small helical spring 15 is compressed between the ball 14 and a shoulder 16 provided around the opening of the bore 8 in the free end of the stem 7. The barrel 9 can slide freely over the stem 7 and an annular sealing ring 17 is compressed in an annular groove in the inner surface of the barrel 9 to ensure the sealing of a first chamber 18 of the valve, defined within the barrel 9 by the free end of the stem 7.

A second chamber 19 of the valve is defined within the bore 2 between the barrel 9 and the disc 10, on the one hand, and the cap 4, on the other hand. The cap 4 is screwed into a screw-threaded bore 20 of the body 1 and this cap 4 itself has a screw-threaded axial bore 21 in which is screwed a rod 22. The end 23 of the rod 22 is substantially reduced in cross-sectional area to enable it to penetrate substantially within the bore 12 as the barrel 9 slides inside the bore 2.

A helical return spring 24 is positioned in the chamber 19, one of its ends abutting the cap 4 and the other end abutting the disc 10.

This spring 24 surrounds the rod 22.

The body 1 has two radial bores 25 and 26 which connect the bore 2 to the exterior of the valve.

In use, when scarcely any fluid pressure is exerted within the bore 8 and consequently the chamber 18, the valve is in the state shown in Figure 1. Only the spring 15 holds the ball 14 on the seat 13 in opposition to the weight of the ball to prevent the ball 14 being displaced when the valve is orientated in various positions in any particular circuit.

As shown in Figure 1, the spring 24 is relaxed and under either no pressure or under very slight compression from the spring 15 acting via the intermediary of the disc 10.

When the fluid pressure within the bore 8 and the chamber 18 rises, the fluid cannot escape from the chamber 18 and an axial force is produced acting on the disc 10 to force the barrel 9 in a direction 28 and, compress the spring 24 proportionate to the barrel's displacement. Simultaneously, the fluid pressure forces the ball 14 against the seat 13, sealing it.

When the fluid pressure reaches a predetermined value, according to the adjustment of the valve, the barrel 9 compresses the spring 24 sufficiently for the end 23 of the rod 22 to contact the ball 14 (see Figure 2).

As the pressure rises above the predetermined value, the barrel 9 compresses the spring 24 further so that the end of the rod 22 removes the ball 14 from its seat 13 (see Figure 3). The fluid can then flow in a direction 29 from the chamber 18 into the chamber 19, where it escapes from the valve via the bore 25. The bore 25 can be connected topipe-work to collect the fluid.

When the tmld pressure falls, the barrel 9 returns to its initial position under the action of the spring 24. The bore 26 maintains a chamber 27 formed between the barrel 9 and the cap 3 at atmospheric pressure so that the sliding of the barrel is not inhibited.

To regulate the calibration of the valve, it is sufficient to screw the cap 4 and the rod 22 further into or out of the body 1.

The graph shown in Figure 6 plots along the abscissa the pressure of the fluid and along the ordinate the force exerted on the seat of a discharge-valve by the fluid pressure.

The line 30 corresponds to the plot for a known type of valve in which the fluid pressure moves an obturating member progressively from its seat in opposition to a spring. It can be seen that the force is inversely proportional to the pressure. This results in a poor sealing of the valve even when the pressure is well below the predetermined adjustment value of the valve.

Also, the greatest force is exerted in the absence of pressure, when sealing of the valve is unnecessary. This force is exerted in a fashion injurious to the surfaces of the contacting members of the valve.

The curve 31 corresponds to the plot for a valve according to the present invention. In the absence of fluid pressure, at point 32, the force exerted is very weak being that exerted by the spring 15. As the pressure increases, the force increases proportionally up to a point 33 corresponding to the pre-determined adjustment value of the valve at which the ball just touches the end 23 of the rod 22. When the pressure increases beyond this value, the force becomes inversely proportional to the pressure but the gradient of the curve is a function of the sections defined between the chamber 18 and the contact circle of the ball 14. More importantly, when compared to a valve giving a plotted line 30, the opening of the present valve occurs at a more precisely defined moment.

In a modification of the invention the ball 14 can be replaced by a frusto-conical valve member 34 so that the valve seat can comprise simply the opening of a bore 35 in the disc 10 (see Figure 4). In this modification, as when using a ball, the presence of a conical contact surface is advantageous because the seat is self-cleaning, particles in suspension in the fluid tending to be automatically eliminated during successive openings and closings of the valve.

In another modification of the invention, the ball 14 is replaced by a disc whose end surface abuts against a seat comprising an annular projection surrounding the opening of a bore 38 in the disc 10 (see Figure 5).

This modification enables a more rapid opening of the valve to be obtained.

WHAT I CLAiM IS: 1. A relief valve comprising a body in which a fluid-tight chamber is adapted to be put into communication with a pressurised fluid circuit, and a valve member within the chamber and resiliently urged against a seat to close the chamber, the seat being disposed on a barrel freely slidable in the body to take up a a balanced condition between fluid pressure forces in the chamber, and the force of a return spring, whereof one end abuts the barrel, an abutment fixed to the body being provided, so as to be contactable by the valve member when the latter is on its seat and moving with the barrel so that - if the fluid pressure in the chamber is nil the return spring is loaded only by the resilient pressure urging the valve member against its seat and is thus practically noncompressed, - if the fluid pressure remains lower than a predetermined calibration value for the valve, the valve member is applied against its seat by the fluid with a force proportional to this fluid pressure and the barrel slides to more or less compress the return spring, - if the pressure is above the predetermined calibration value of the valve, the barrel further compresses the return spring causing the valve member to contact the abutment whereby it is spaced from its seat.

2. A valve according to claim 1, in which the body comprises a central bore, whereof one end is closed by a cap having an integral coaxial stem which extends into a central bore of the barrel, the cap being provided with an axial through-hole to permit the valve to be placed in communication with the pressurised fluid circuit and the fluidtight chamber being within the barrel bore and being delimited by the end of the stem, a seal being provided between the cylindrical surface of the stem and the barrel.

3. A valve according to claim 1 or 2, in which the fluid-tight chamber encloses a small helical spring constantly compressed between the valve member and the end of the stem to provide the resilient loading

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. barrel's displacement. Simultaneously, the fluid pressure forces the ball 14 against the seat 13, sealing it. When the fluid pressure reaches a predetermined value, according to the adjustment of the valve, the barrel 9 compresses the spring 24 sufficiently for the end 23 of the rod 22 to contact the ball 14 (see Figure 2). As the pressure rises above the predetermined value, the barrel 9 compresses the spring 24 further so that the end of the rod 22 removes the ball 14 from its seat 13 (see Figure 3). The fluid can then flow in a direction 29 from the chamber 18 into the chamber 19, where it escapes from the valve via the bore 25. The bore 25 can be connected topipe-work to collect the fluid. When the tmld pressure falls, the barrel 9 returns to its initial position under the action of the spring 24. The bore 26 maintains a chamber 27 formed between the barrel 9 and the cap 3 at atmospheric pressure so that the sliding of the barrel is not inhibited. To regulate the calibration of the valve, it is sufficient to screw the cap 4 and the rod 22 further into or out of the body 1. The graph shown in Figure 6 plots along the abscissa the pressure of the fluid and along the ordinate the force exerted on the seat of a discharge-valve by the fluid pressure. The line 30 corresponds to the plot for a known type of valve in which the fluid pressure moves an obturating member progressively from its seat in opposition to a spring. It can be seen that the force is inversely proportional to the pressure. This results in a poor sealing of the valve even when the pressure is well below the predetermined adjustment value of the valve. Also, the greatest force is exerted in the absence of pressure, when sealing of the valve is unnecessary. This force is exerted in a fashion injurious to the surfaces of the contacting members of the valve. The curve 31 corresponds to the plot for a valve according to the present invention. In the absence of fluid pressure, at point 32, the force exerted is very weak being that exerted by the spring 15. As the pressure increases, the force increases proportionally up to a point 33 corresponding to the pre-determined adjustment value of the valve at which the ball just touches the end 23 of the rod 22. When the pressure increases beyond this value, the force becomes inversely proportional to the pressure but the gradient of the curve is a function of the sections defined between the chamber 18 and the contact circle of the ball 14. More importantly, when compared to a valve giving a plotted line 30, the opening of the present valve occurs at a more precisely defined moment. In a modification of the invention the ball 14 can be replaced by a frusto-conical valve member 34 so that the valve seat can comprise simply the opening of a bore 35 in the disc 10 (see Figure 4). In this modification, as when using a ball, the presence of a conical contact surface is advantageous because the seat is self-cleaning, particles in suspension in the fluid tending to be automatically eliminated during successive openings and closings of the valve. In another modification of the invention, the ball 14 is replaced by a disc whose end surface abuts against a seat comprising an annular projection surrounding the opening of a bore 38 in the disc 10 (see Figure 5). This modification enables a more rapid opening of the valve to be obtained. WHAT I CLAiM IS:

1. A relief valve comprising a body in which a fluid-tight chamber is adapted to be put into communication with a pressurised fluid circuit, and a valve member within the chamber and resiliently urged against a seat to close the chamber, the seat being disposed on a barrel freely slidable in the body to take up a a balanced condition between fluid pressure forces in the chamber, and the force of a return spring, whereof one end abuts the barrel, an abutment fixed to the body being provided, so as to be contactable by the valve member when the latter is on its seat and moving with the barrel so that - if the fluid pressure in the chamber is nil the return spring is loaded only by the resilient pressure urging the valve member against its seat and is thus practically noncompressed, - if the fluid pressure remains lower than a predetermined calibration value for the valve, the valve member is applied against its seat by the fluid with a force proportional to this fluid pressure and the barrel slides to more or less compress the return spring, - if the pressure is above the predetermined calibration value of the valve, the barrel further compresses the return spring causing the valve member to contact the abutment whereby it is spaced from its seat.

which urges the valve member against its seat, this spring being much less powerful than the barrel return spring.

4. A valve according to claim 2 or 3, in which the valve member is constituted by a ball and the seat is constituted by a frustoconical bore in a disc carried by the barrel.

5. A valve according to claim 2 or 3, in which the valve member is of frusto-conical shape and the seat is constituted by the orifice of a hole in the barrel.

6. A valve according to claim 2 or 3, in which the valve member has at its end a plane annular surface adapted to abut against the face of a circular boss constituting the seat.

7. A valve according to any one of claims 1 to 6, in which the return spring of the barrel is constituted by a helical spring, whereof one end abuts a shoulder of the body, at the end of the central bore, and whereof the other end abuts the slidable barrel.

8. A valve according to claim 7, in which the shoulder against which the return spring abuts is provided on a cap closing the corresponding end of the central bore of the body, this cap carrying a rod extending axially into the bore and adapted to engage with substantial play through the barrel by passing in an axial bore of the barrel, this axial hole traversing the seat, the free end of the rod constituting the abutment for the valve member, at least one fluid leakage orifice being provided in the body to allow escape of fluid passing the seat.

9. A valve according to claim 8, in which the cap carrying the shoulder is screwed into a screw-threaded bore of the valve and can be used to determine the calibration value of the valve by rotation of the cap.

10. A valve according to claim 8 or 9, in which the rod is screwed into a screwthreaded bore of the cap and can be used to determine the calibration of the valve by varying the longitudinal position of its free end.

11. A relief valve substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.