GB2359609A

GB2359609A - A pressure relief valve

Info

Publication number: GB2359609A
Application number: GB0000151A
Authority: GB
Inventors: Robert Dews
Original assignee: Renold PLC
Current assignee: Renold PLC
Priority date: 2000-01-06
Filing date: 2000-01-06
Publication date: 2001-08-29
Also published as: GB0000151D0

Abstract

An in-line pressure relief valve comprises a body 1 with an open bore 2 extending therethrough, at least one transverse relief passage 9 that extends from the bore to an opening, and a resilient sealing collar 6 disposed over at least a part of the valve body including the openings. In use, the collar is expandible so that when the pressure in the bore exceeds a predetermined value the collar expands allowing the at least one transverse relief passage to communicate with the surroundings. The valve may be bi-directional, the at least one transverse relief passage may be radially disposed and the collar may be a friction or interference fit over the body. The valve may be used in conjunction with a telescopic bracing strut of the piston and cylinder type.

Description

2359609 1 A PRESSURE RELEASE VALVE The present invention relates to a

pressure release valve and to a hydraulic or pneumatic cylinder assembly of the kind that is used to effect extension or retraction of telescopic bracing struts and is fitted with such a valve.

Bracing struts are commonly used as part of shoring equipment that is designed to support the surrounding earth during ground excavations so as to prevent subsidence. The bracing struts typically extend across the width and/or along the length of an excavated trench and bear against support plates or walls that line the excavation and are biased into an extended position so as to hold the plates or walls in place against the pressure of the surrounding earth- Such bracing struts are telescopically extensible or retractable by means of a hydraulic or pneumatic cylinder that is disposed inside the strut. The bracing struts can be arranged into any appropriate configuration along the width, length and depth of the excavated hole.

A hydraulic or pneumatic cylinder of the kind described above has inlet and outlet valve assemblies for the supply and return of working fluid. The valve assemblies each have quick-connect couplings to which, in use, are connected the fluid supply and return hoses of a pump. The valve assemblies are usually designed such that when the hoses are not connected they are closed so as to prevent leakage of fluid from the cylinder.

There is a disadvantage associated with the cylinder designs described above in that if outlet hose is not connected properly the outlet valve will remain closed or at least partially open. Thus, in use, whilst the supply fluid passes through the inlet valve and into the cylinder to extend the piston and therefore the strut, the return fluid from the other side of the piston is unable to escape at sufficient rate. This results in an increase in fluid pressure in the cylinder and when the pressure reaches a certain value it causes distortion of the cylinder wall or damage to seals and therefore failure of the equipment.

It is an object of the present invention to obviate or mitigate the aforesaid disadvantage.

2 According to a first aspect of the present invention there is provided an in-line pressure relief valve comprising a body with an open bore extending therethrough, at least one transverse relief passage that extends from the bore to an opening at the surroundings and a resilient sealing collar disposed over at least part of the valve body so as to seal the opening and prevent communication of the bore with the surroundings via the transverse relief passage, wherein the collar is expansible so that when the pressure in the bore exceeds a predetermined value relative to the surroundings the collar expands so as to open the transverse relief passage to the surroundings.

According to a second aspect of the present invention there is provided a piston and cylinder assembly comprising a cylinder in which a piston is reciprocally disposed, a first variable volume chamber for supply fluid on one side of the piston and a second variable volume chamber for return fluid on the other side of the piston, a fluid inlet in communication with the first chamber via an inlet valve and a normally closed fluid outlet in communication with the second chamber via an outlet in-line pressure relief valve, wherein the outlet pressure relief valve comprises a body with an open bore extending therethrough which, in use, connects the second chamber to a reservoir of return fluid, at least one transverse relief passage that extends from the bore to an opening at the surroundings and a resilient sealing collar disposed over at least part of the valve body so as to seal the opening and prevent communication of the bore with the surroundings via the transverse relief passage, wherein the collar is expansible so that when the pressure in the bore exceeds a predetermined value relative to the surroundings the collar expands so as to open the transverse relief passage to the surroundings.

According to a third aspect of the present invention there is provided a telescopic bracing strut being telescopically movable by a piston and cylinder assembly as described above.

A specific embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

3 Figure 1 is a side view of a pressure relief valve according to the present invention; Figure 2 is an end view of the valve of figure 1; Figure 3 is a longitudinal sectioned view of a piston and cylinder rod assembly incorporating the pressure relief valve of figures 1 and 2; Figure 4 is an end view of the assembly of figure 3; and Figure 5 is a longitudinal view of a telescopic bracing strut fitted with the piston and cylinder rod assembly of figures 3 and 4.

Referring now to the drawings, the pressure relief valve 1 is generally cylindrical with a central circular bore 2 extending coaxially therethrough from an inlet 3 to an outlet 4. The inlet 3 and outlet 4 ends of the valve 1 are of reduced diameter and are externally threaded so as to allow connection to other apparatus.

The main part of the valve body comprises a first cylindrical section 5 on which a resilient nylon annular collar 6 is mounted with a friction (e. g. interference) fit and a second section 7 that has a plurality of peripheral flats 8 that are designed to co-operate with an installation tool (not shown).

Four equi-angularly spaced radial passages 9 pass through the valve body 1 and connect the central bore 2 to the interior surface of the collar 6.

In use, the central bore 2 carries pressurised fluid such as air or hydraulic oil from inlet to outlet. In circumstances (such as those described later) where the outlet 4 is closed the fluid pressure may increase and the fluid in the radial passages 9 bears against the interior surface of the collar 6. The collar 6 is carefully designed such that when the fluid in the passages 9 reaches a predetermined pressure with respect to the surrounding atmosphere it expands slightly so as to allow the fluid to leak past the collar 6 to atmosphere thereby relieving the pressure in the bore 2. When the pressure falls below the predetermined valve the collar 6 contracts so as to re-seal the radial passages 9.

An exemplary application for such a pressure relief valve 1 will now be described with reference to a piston and cylinder assembly illustrated figures 3 and 4. A piston 10 comprising a head 11 and a hollow piston rod 12 is slidable reciprocally 4 in a cylinder tube 13. One end of the cylinder 13 is connected to a first trunnion block 14 by which the assembly is connected to other apparatus. The other end of the cylinder 131 has a gland sleeve 15 fitted with a bearing 16 and a sealing ring 17 so as to allow the piston rod 12 to slide relative thereto without fluid leakage. The piston rod 12 is concentrically disposed with respect to the cylinder 13 and separated therefrom by an annular clearance 18. A conduit (not shown) through the piston rod 12 connects the annular clearance 18 to the interior of the piston rod 12. A second trunnion block 19 is connected to the free end of the piston rod 12 and closes the interior thereof.

The first trunnion block 14 has fluid inlet 20 and outlet 21 connectors which use are connected to the supply and return hoses (not shown) of a fluid pump. The fluid outlet 21 has an in-line pressure relief valve 1 according to that described in relation to figures 1 and 2 above. The first trunnion block 14 has internal conduits (not shown) that respectively connect the inlet 20 to a first variable volume chamber 22 defined on a first side of the piston head 11 (the chamber is shown closed in figure 3) and the outlet 21 to a second variable volume chamber 23 defined the other side of the piston head 11 by the annular clearance 18 in combination with the fixed volume inside the piston rod 12. The second variable chamber 23 is connected to the internal conduits in the first trunnion block 14 by a return pipe 24 that is fixed thereto and extends through the piston head 11 and into the piston rod 12 interior. The piston head 11 has a bore 25 in which the return pipe 24 is slidably received, the bore 25 having several annular grooves 26 in which are disposed an annular bearing 27 and a sealing ring 28. The outer surface of the piston head 11 also has annular grooves 29 in which there are disposed sealing rings 30 and a bearing 31 so as to accommodate sliding movement of the head 11 relative to the cylinder 13.

In use the inlet and outlet 20, 21 are connected respectively to the supply and return hoses (not shown) of a fluid pump by means of quickconnect couplings. The couplings are of a well-known design which ensures that the inlet and outlet 20, 21 are closed until such time as the hoses are properly connected. M7hen the pump is operated to extend the piston and cylinder assembly, fluid is supplied via the inlet 20 to the first side of the piston head 11. This forces the piston 10 to slide relative to the cylinder 13 and the return pipe 24 thereby increasing the volume of the first variable volume chamber 22 and decreasing the volume of the second chamber 23. The reduction in volume in the second chamber 23 forces fluid into the return pipe 24 and out of the outlet 21 back to the pump. In the instance where the return hose is not connected properly and therefore the outlet valve is closed or only partially open the pressure in the return pipe 24 and the throughbore 2 of the pressure relief valve 1 increases until the collar 6 expands as described above and releases the fluid pressure. The relief valve 1 thus prevents the cylinder 13 or seals from being fouled by the increased pressure. When the assembly is extended to the required length a lock valve 40 of conventional design is operated to hold the pressures inside the respective chambers.

When it is necessary to retract the assembly the pump is reversed so as to reverse the flow of fluid through piston and cylinder assembly. The pressure relief valve 1 is thus bi-directional in operation.

The provision of an in-line pressure relief valve 1 of this kind obviates the need additional connectors such as tee-fittings or the like, and additional working parts.

Figure 5 shows the cylinder fitted inside a telescopic bracing strut. The trunnion blocks 14, 19 are each connected to a respective box beam 41, 42 by means of a connecting pin 43 that passes through a bore 44 in each trunnion block 14, 19. The respective box beams 41, 42 slide relative to one another during extension or retraction of the piston and cylinder assembly.

It will be appreciated that numerous modifications to the above described design may be made without departing from the scope of the invention as defined in the appended claims. In particular, the pressure relief valve may have other in-line applications in addition to the exemplary embodiments described above. Moreover, it will be appreciated that the predetermined value at which pressure is to be released from the valve can be varied by changing the components or structure of the valve. For example, the following can be varied in isolation or in any combination: the 6 number and size (diameter) of radial passages; the material of (and hence the physical properties) the collar; the dimensions of the collar; or the fit between the collar and valve body.

7

Claims

An in-line pressure relief valve comprising a body with an open bore extending therethrough, at least one transverse relief passage that extends from the bore to an opening at the surroundings and a resilient sealing collar disposed over at least part of. the valve body so as to seal the opening and prevent communication of the bore with the surroundings via the transverse relief passage, wherein the collar is expansible so that when the pressure in the bore exceeds a predetermined value relative to the surroundings the collar expands so as to open the transverse relief passage to the surroundings.

An in-line pressure relief valve according to claim 1, wherein the valve is bidirectional.

An in-line pressure relief valve according to claim 1 or 2, wherein the or each transverse relief passage is radially disposed.

An in-line pressure relief valve according to claim 1, 2 or 3, wherein the collar is a friction fit over the valve body.

A piston and cylinder assembly comprising a cylinder in which a piston is reciprocally disposed, a first variable volume chamber for supply fluid on one side of the piston and a second variable volume chamber for return fluid on the other side of the piston, a fluid inlet in communication with the first chamber via an inlet valve and a normally closed fluid outlet in communication with the second chamber via an outlet in-line pressure relief valve, wherein the outlet pressure relief valve comprises a body with an open bore extending therethrough which, in use, connects the second chamber to a reservoir of return fluid, at least one transverse relief passage that extends from the bore to an opening at the surroundings and a resilient sealing collar disposed over at 8 least part of the valve body so as to seal the opening and prevent communication of the bore with the surroundings via the transverse relief passage, wherein the collar is expansible so that when the pressure in the bore exceeds a predetermined value relative to the surroundings the collar expands so as to open the transverse relief passage to the surroundings.

6. A telescopic bracing strut being telescopically movable by a piston and cylinder assembly according to claim 5.

7.

A pressure relief valve substantially as hereinbefore described with reference to the accompanying drawings.

8. A piston and cylinder assembly substantially as hereinbefore described with reference to the accompanying drawings.

9. A telescopic bracing strut substantially as hereinbefore described with reference to the accompanying drawings