GB2071807A - Hydraulic shock-absorbing arrangement suitable for supporting pipes - Google Patents

Abstract

A shock-absorbing support arrangement comprises a cylinder 1, filled with hydraulic fluid, having a hollow piston 2 with a plurality of ports 15, 16 in each end face 12, 14. Valve plates 17, 18 are each biassed away from the ports in each end face, and are dimensioned so as to be capable of closing all of the ports in one face or the other simultaneously. Slow piston movement does not affect the valve plates. Sudden shock on the piston rod moves one or other plate to close all its ports simultaneously. Fluid flow normally takes place past both outer and inner periphery of each plate thus allowing closer spacing and therefore quicker response than prior art proposals. Accessible screws 20 permit easy adjustment. The parts are disposed in a circle. <IMAGE>

Description

SPECIFICATION Hydraulic shock-absorbing arrangement suitable for pipe conduit systems The invention relates to a hydraulic shock absorbing arrangement suitable for pipe conduit systems, of the type which supports the pipe conduit system so as to permit slow displacement (eg. due to thermal expansion) but provide rigid support against shock displacement, eg. due to earthquake or the like.

A shock-absorbing arrangement suitable for this purpose is disclosed in German Published Specification 2721890. In this prior proposal a cylinder filled with hydraulic fluid is provided with a hollow piston having a port in each end face whereby hydraulic fluid can pass from one side of the cylinder through the hollow piston space, to the other. Springbiassed ball-valve closure members are provided for each port, being individually replaceable with value inserts of difference calibration. Within the hollow piston there is a volume-compensating bellows member, vented to atmosphere down through a piston rod itself passing out through an end wall of the piston. The cylinder is connected, (directly or indirectly) either to the pipe conduit system or to a stationary abutment, and the protruding piston rod is connected to the other of these members.Thus slow movements due to thermal expansion allow fluid to flow through both parts. Sudden shocks cause one of the ball valves to close its valve, due partly to inertia and partly to entrainment by the sudden fluid flow due to initial attempted movement, whereby the pipe conduit system is rigidly supported.

Under normal conditions, this system operates satisfactorily. However, the setting resistance of the arrangement can be altered only be unscrewing inserts containing the valve balls from the pistons and thereafter replacing them by differently calibrated inserts. Moreover, for some purposes it would be convenient if the response time of the arrangement could be shortened.

It is an object of the present invention to improve the valve for the restrictor port so that flow resistance can be regulated in a manner simpler than hitherto and so that furthermore the operating response is shortened. It is a further object of the invention to provide as low a resistance to motion when the piston performs the normal movements resulting from thermal expansion of the pipe conduit system.

According to the invention there is provided a hydraulic shock absorbing arrangement suitable for supporting and mounting pipe conduit systems comprising: a hydraulic cylinder closed at each end face and filled with hydraulic fluid; a piston adapted to slide within said cylinder, having a first and second piston end face defining an internal space therebetween, each of said piston end faces being provided with a plurality ports thereby placing said internal space in communication with the interior of the cylinder to either side of the piston, a first and second annular plate located parallel to and biassed to be spaced outwards from the first and second piston end face respectively, each said plate being slideable towards its adjacent piston end face to constitute a common closure member for all of said ports therein; a deformable hollow compensation member located within said piston internal space and vented to atmosphere; and a piston rod attached to one piston end face and sealingly slidable through one cylinder end face.

This offers the advantage that the setting resistance can be adjusted by a simple change of distance between the annular plate and the end face of the piston. Another advantage is due to the fact that the same annular plate acts to close a plurality of ports, so that a large number of flow paths are available for the hydraulic medium and the resistance is exceptionally low against the slow displacement movements which result from thermal expansion.

It is advantageous for the axial guidance of the annular plate to be provided by a plurality of guide screws which are secured in the respective piston end face and are distributed around the circumference of said annular plate.

It has also been found convenient if the spring force for maintaining the annular plate in the open state is provided by compression springs around the guide screws. In general, three compression springs distributed symmetrically over the circumference are sufficient.

They offer the advantage that the arrangement continues to operate reliably even in the event of fracture of one spring, since the two remaining springs are sufficient to actuate the annular plate. In known valve systems each valve member is dependent on the spring associated therewith.

For manufacturing reasons it is advisable for the guide screws which provide axial guidance for the annular plate to be disposed in one part of the restrictor ports. It is thus possible in one operation to provide each piston end face with 12 restrictor ports, three of which are subsequently used to receive the guide screws.

The annular plate may have internal and external diameters such in use hydraulic fluid can flow past both the internal and external peripheries thereof. In practice, this doubles the exit cross-section for the hydraulic fluid flowing from the gap between the annular plate and the piston. This doubling of the cross-section offers the advantage that the annular plate can be disposed substantially closer to the piston and its distance can be reduced in practice to half the valve conventionally employed for flow on one side. This means that the closing travel over which the annular plate has to traverse in the event of sudden shocks to the pipe conduit system is only half as long. The arrangement therefore responds twice as fast.By adopting this construction it has been found possible to restrict the movement of the piston rod to 1.5 to 2 mm in the event of sudden surge loading or in the event of load changes.

Further details and advantages of the subject of the invention are disclosed in the description hereinbelow of an exemplified embodiment with reference to the accompanying drawing which shows a longitudinal section through a shock absorbing arrangement according to the invention.

The drawing shows a hydraulic cylinder 1 and a piston 2, which is axially slideable therein and whose piston rod 3 is axially slideably guided in a guide 4 at one end face of the hydraulic cylinder 1. The piston rod 3 is surrounded by sealed bellows 5, connected in liquid-tight manner at one end to the piston 2 and at the other end to the end (not shown) of the guide 4 disposed in the cylinder chamber. The clear internal diameter of the sealed bellows 5 is slightly greater than the external diameter of the piston rod 3. The purpose of the sealed bellows 5 is to prove a hermetic closure between the cylinder chamber and the surrounding zone so that no hydraulic fluid is able to escape outwardly along the piston rod 3 where it passes through the end of the cylinder chamber.

The piston 2 is constructed as a hollow piston with internal compensating bellows 8, mounted on the internal wall of the piston at the piston rod end, disposed coaxially in the internal chamber 7 of said piston. The interior of the compensating bellows 8 communicates via an axial bore 10 of the piston rod 3 with atmosphere.

The cylinder chambers 6 and 13 are located one to each side of the piston 2 and communicate with each other through the internal chamber 7 of the piston by means of plurality of axial ports 15 or 16 in the piston end faces 12 and 14 respectively. In each location the axial ports 15, or 16, are positioned to open at positions located around a circular arc, preferably coaxially with the piston axis, these positions most conveniently having a uniform distance between them. In the exemplified embodiment the diameter of the port is approximately 34 mm but this can of course be substantially larger for larger shock absorbing arrangements.

At these positions. all ports in each end face 12 or 14 are restricted to a greater or lesser extend by means of a common annular plate 17 or 18 respectively The internal and external diameters of the said annular plates 17 and 18 are such that in the closed position they completely cover the ports 15 or 16 associated therewith. Each of said plates is guided to be axially slideable in relation to its associated piston end face by means of a plurality of screw members 19 or 20 distributed around its circumference. Compression springs (which take the form of helical springs 21 and 22 disposed around the screw members 19 and 20 in the exemplified embodiment, but which can also be differently constructed and positioned) urge each of the two annular plates away from the relevant piston end face into a position where the ports are open.The gap between the annular plates 17, 18 and the respective piston end faces associated therewith, normally being of the order of magnitude of a few tenths of a millimetre, is defined by the effective length of the screwfasteners 19 or 20.

Operation of the system is as follows: Normal slow motion of the supported pipe conduit systems eg. due to thermal expansion are accompanied by a slow displacement of the piston 2, allowing hydraulic fluid to flow without obstruction from one cylinder chamber 6 into the other cylinder chamber 13 or vice versa, depending on the direction in which the piston 2 is displaced. Compensating bellows 8 expands or contracts to compensate for the volume of piston rod 3 entering or leaving the cylinder, as known in the prior art, the internal air venting or drawing from atmosphere accordingly. Since the hydraulic medium is able to flow past the inner periphery as well as past the outer periphery of the annular plate, when flowing through the gap between the piston end face and the associated annular plate, it follows that the flow resistance is exceptionally low.The shock absorbing arrangement according to the invention is therefore characterized by particularly low setting forces.

However, in the event of a sudden motion of the piston 2, for example to the left on the drawing, the annular plate 17 will be thrust against the force exerted by the springs 21, on to the piston end face 12 to block the flow. This takes place on the one hand because of the sudden flow of hydraulic fluid discharged from the cylinder chamber 13 and on the other hand because of the inertia of the plate. Annular plate 18 operates correspondingly for the reverse direction.

Because of the flow, as described above past both peripheries of the annular plate, the operating time of the shock absorbing arrangement according to the invention is much shorter than in conventional shock-absorbing arrangement. This is because flow past both peripheries of the annular plates permits of operation, when the ports are in the open position, with an exceptionally narrow gap of a few tenths of a millimetre so that the closing travel of the valve plate is substantially shorter than in known prior art proposals of this type.

The device continues to operate even if one of the compression springs 21 or 22 is broken, because the remaining springs will again open the annular plate.

Manufacture of the valves is considerably cheaper because it is not necessary to use complicated components.

Claims (6)

1. A hydraulic shock absorbing arrangement suitable for supporting and mounting pipe conduit systems comprising: a hydraulic cylinder closed at each end face and filled with hydraulic fluid; a piston adapted to slide within said cylinder, having a first and second piston end face defining an internal space therebetween, each of said piston end faces being provided with a plurality ports thereby placing said internal space in communication with the interior of the cylinder to either side of the piston; a first and second annular plate located parallel to and biassed to be spaced outwards from the first and second piston end face respectively, each said plate being slideable towards its adjacent piston end face to constitute a common closure member for all of said ports therein; a deformable hollow compensation member located within said piston internal space and vented to atmosphere; and a piston rod attached to one piston end face and sealingly slidable through one cylinder end face.

2. A shock absorbing arrangement as claimed in Claim 1 further comprising a plurality of guide screws, distributed around the circumference of each annular plate and secuied in the respective piston end face to constitute axial guide means for the annular plate.

3. A shock absorbing arrangement as claimed in Claim 2 further comprising a compression spring around at least one guide screw as a biassing member for each annular plate.

4. A shock absorbing arrangement as claimed in Claim 2 in which the said guide screws which provide axial guidance for the annular plate are each themselves disposed in a partition of one of said ports.

5. A shock absorbing arrangement as claimed in Claim 1 in which the internal and external diameter of said annular plate is such that in use hydraulic fluid flows past both the internal and external peripheries thereof.

6. Surge decelerator according to Claim 1 characterised in that the axial guide means for the annular plate (17, 18)are provided by a plurality of guide screws (19, 20) distributed over the circumference of said annular plate and secured in the piston end face (12, 14) and that the radial ring width is adapted to the diameter of the restrictor ports (15 or 16) so that in the open state, the hydraulic fluid can flow around the annular plate radially from the inside as well as radially from the outside.