GB2147083A

GB2147083A - Cylinder construction for jack

Info

Publication number: GB2147083A
Application number: GB08423060A
Authority: GB
Inventors: William Stroud
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-09-21
Filing date: 1984-09-12
Publication date: 1985-05-01
Also published as: GB8423060D0

Abstract

A telescopically extensible piston and cylinder assembly (12, 10), such as a jack, comprises a piston (16) axially reciprocable within a cylinder member (14) the cylinder member having an inner tubular portion (26) of relatively weak material in sealing engagement with the piston, and an outer reinforcing portion (28) of relatively strong material which surrounds the tubular portion and reinforces against deformation or damage caused by fluid pressure in the inner tubular portion. <IMAGE>

Description

SPECIFICATION Piston and cylinder assembly This invention relates to a piston and cylinder assembly. More particularly, the invention relates to a piston and cylinder assembly suitable for use as, or as part of, a jack, wherein the cylinder is subjected to high internal fluid properties.

According to the invention a telescopically extensible piston and cylinder assembly comprises a piston axially reciprocable within a cylinder member, the cylinder member having an inner tubular portion of relatively weak material in sealing engagement with the piston, and an outer reinforcing portion of relatively strong material which surrounds the tubular portion and reinforces it against deformation or damage caused by fluid pressure in the inner tubular portion.

In this regard "relatively weak" and "relatively strong" refer to the tensile strength of the materials in question, the relatively weak material having a lower tensile strength than the relatively strong material.

The tubular portion may thus be of a plastics material, the reinforcing portion being of metal. The plastics material may be selected from the group consisting in polyvinyl chloride (PVC) and glass fibre reinforced resin, the metal being steel.

The tubular portion may be a pipe length eg of smooth-sided plastics piping, the reinforcing portion also being a pipe length, the tubular portion being receivable within the reinforcing portion with a sufficiently close fit, eg a sliding fit or closer, to prevent fluid pressure in the tubular portion from expanding the tubular portion sufficiently to affect the sealing engagement between the piston and said tubular portion.

Opposite ends of the reinforcing portion may be closed off by closure members, which may be removable, which engage opposite ends of the tubular portion to locate it axially in the reinforcing portion, at least one of the closure members having the piston passing sealingly therethrough, and at least one of the closure members having a passage therethrough for working fluid. This construction permits easy replacement of the tubular portion, eg after it is worn, and in use each passage for working fluid will be connected to a source of working fluid under pressure, eg a pump or compressor. The closure members may thus be plugs which are externally screw threaded and which screw into the ends of the reinforcing member, which are internally screw threaded.

The piston may be provided with at least one flexible cup seal for sealing engagement with the inside of the tubular member, the cup seal facing away from a rigid support therefor on the piston.

The assembly may form part of a jack. as it is particularly suitable for the high pressures encountered in the working fluid in the interior of a piston and cylinder type jack.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows a sectional side elevation of a piston and cylinder assembly according to the invention forming part of a jack; and Figure 2 shows a sectional side elevation of another piston and cylinder assembly according to the invention.

In Fig. 1 of the drawings, reference numeral 10 generally designates a piston and cylinder assembly in accordance with the invention and forming part of a jack. The jack is thus designated 10 and comprises the piston and cylinder assembly which is generally designated 1 2. The piston cylinder assembly 12 in turn comprises a cylinder member 14 and a piston 16.

The piston 1 6 is a circular cylindrical steel post or rod, telescopically reciprocably slidable, lengthwise, in the interior of the cylinder member 14. In Fig. 1 it is shown projecting axially outwardly, at 18, from one end of the cylinder member 14.

The opposite end of the piston 16, in the interior of the cylinder member 14, is shown provided with a flexible elastomeric cup seal 20 of the same nominal diameter as the piston 16, and held concentrically in position on the end of the piston 1 6 by a bolt 22 provided with a washer 24 and screwed axially into a centrally provided tapped passage in said end of the piston 1 6. The end of the piston 1 6 forms a rigid support for the cup washer 24, and the washer faces away from this support.

The cylinder member 14 comprises an inner tubular portion 26 and an outer reinforcing portion 28. The tubular portion 26 is a PVC pipe, and the reinforcing portion 28 in turn is a steel pipe. The outer diameter of the tubular portion 26 is substantially the same as, or fractionally larger than, the inner diameter of the reinforcing portion 28, so that the tubular portion 26 is a close frictional or press fit in the reinforcing portion 28. The material of the PVC pipe has a substantially lower tensile strength than that of the steel pipe.

The end of the tubular portion 26 into which the piston 1 6 projects is held in position in the reinforcing portion 28 by an annu lar locating plug 30. The locating plug or ring 30 is externally screw threaded, and engages corresponding threads on the inside of the associated end of the reinforcing portion 28, and abuts the adjacent end of the tubular portion 26.The internal opening through the plug 30 permits the piston 1 6 to slide therethrough, so that it can project outwardly, as shown at 1 8. The opposite end of the reinforcing portion 28 is also screw threaded, and is shown connected to a roughly cylindrical steel connector in the form of a plug 32 having the same outside diameter as the reinforcing portion 28, and having a spigot 34 screwed into the adjacent end of the reinforcing portion 28, the connection being provided with two O-ring seals 36 respectively between the plug 32 and the associated ends of the tubular portion 26 and reinforcing portion 28.

The connector 32 has a further spigot 38 projecting in the opposite direction, and screwed into the end of a steel pipe 40, similar to the steel pipe of the reinforcing portion 28, and which forms an axial extension to the piston and cylinder assembly 1 2.

The connection between the pipe 40 and spigot 38 is also provided with an O-ring seal, designated 42. The spigot 38 in turn has a co-axial socket 44 which is threaded and which receives the threaded end of a steel tube 46. The tube 46 has a cylindrical rod 48 reciprocable therein and is provided with a pair of axially spaced O-ring seals 50, 52 located in annular circumferential grooves in its outer surface and engaging sealingly against the inside of the tube 46, in which the rod 48 is a sliding fit. The rod 48 is substantially the same length as the tube 46 and its end remote from the connector 32 is provided with a steel eye 54 welded thereto.The end of the tube 46 remote from the connector 32 in turn is supported and spaced co-axially within the pipe 40, by an annular spacer 56 which is welded to the inside of the pipe 40 and to the outside of the tube 46 as at 58, in fluid-tight fashion.

The pipe 40 has a radial opening therethrough (not shown) of the same or slightly larger diameter than the opening through the eye 54, and in register therewith when the rod 48 is telescoped fully inwardly into the tube 46, as shown in Fig. 1. The diametrically opposite side of the pipe 40 is provided with an axially extending slot 60, whose width is the same as or slightly larger than the diameter of the opening through said eye 54.

The connector 32 is provided with an axial passage 62 which provides an inlet from the tube 46 into the cylinder member 14. The passage 62 tapers as at 64 to provide a frusto-conical valve seat for a ball valve 66, which is located in the broader part of the passage 62 by an annular insert 68, which is a press fit in the broader part of said passage 62. The valve 66 acts as a non-return inlet valve into the cylinder member 14.

The connector 32 further has a diametrical passage 70 which intersects the broader part of the passage 62, between the insert 68 and seat 64. The passage 70 in turn has a tapered part as at 72, which forms a frusto-conical valve seat for a ball valve 74. The seat 72 is to one side of the passage 62, and the ball 74 is located between said passage 62 and the seat 72, and is held in position in the broader part of the passage 70, by the ball of the valve 66. The narrow part of the passage 70 is connected by a passage 76 to the interior of the pipe 40, outside the tube 46.

The narrow part of the passage 70, at its end opposite the ball valve 74, is countersunk at 78, the countersink having a narrow inner portion, which opens into the narrow portion of the passage 70, and a broader threaded outer portion.

A pressure relief screw 80 has an externally threaded slotted head 82 which screws into the threaded outer portion of the countersink 78, and a shank 84 which fits with a sliding fit into the unthreaded narrow inner portion of the countersink 78. The shank 84 is provided with a circumferential groove carrying an 0ring seal 86 which seals against said unthreaded inner portion of the countersink 78.

The shank 84 in turn has an axially outwardly projecting probe or pin 88 which is receiveable with clearance in the narrow portion of the passage 70 and which is engageable with the ball of the valve 74.

In this regard it will be appreciated that the relief screw 80 is shown in an exploded view, axially outwardly of its operative postion in which said head 82 engages the threaded outer portion of the countersink 78.

The broad portion of the passage 70, on the opposite side of the ball valve 66 from the ball valve 74 is provided with a closure in the form of a grub screw 90.

The jack 10 of Fig. 1 in use can act as a building prop for raising and holding up shuttering during building.

In use, the interior of the pipe 40 outside the tube 46 and between the connector 32 and spacer 56, will be filled with a suitable hydraulic fluid such as water, eg via the passage 70 and passage 62, the passage 76 and countersink 78 forming an air outlet. In this regard it should be noted that the interior of the tube 46 is connected to the interior of the pipe 40 by a radial hole 92 through the wall of the tube 46. The reservoir 94 constituted by the interior of the pipe 40 outside the tube 46 will be filled with sufficient hydraulic fluid so that it is entirely filled with fluid when the rod 48 is in its axially inner most position in the tube 46 as shown in Fig.

1 of the drawings, and when the piston 1 6 is in its axially innermost position with the seal 20 adjacent the spigot 34 of the connector 32 (unlike the condition shown in Fig. 1 of the drawings, where the piston and cylinder assembly 1 2 has been extended somewhat).

In this condition, with the rod 48 fully retracted into the tube 46 and the piston 1 6 including its end at 18, fully retracted into the cylinder member 14, the jack 10 is ready for use, the reservoir 94 being filled with hydrau lic fluid and having all gas and air excluded therefrom, the grub screw 90 being in position as shown in the drawing, and the relief screw 80 being screwed partially into the threaded broad outer portion of the countersink 78, so that its probe 88 does not project from the narrow portion of the passage 70 and does not engage the ball 74.

The jack 10 is then inserted into position so that the upper end 96 of the pipe 40 is in contact with a load, such as shuttering, to be jacked upwardly, and the lower end of the reinforcing portion 28 of the cylinder member 1 4 is in contact with a support, such as a floor.

To operate the jack 10, a suitable lever such as a crowbar, is inserted through the slot 60 in the pipe 40, through the eye 54, and then through the diametrically opposed opening through the pipe 40. Reciprocation of the lever along the slot 60, causes reciprocation of the rod 48 in the tube 46. The rod 48 and tube 46 in fact act as a piston and cylinder type pump, and pump hydraulic fluid from the reservoir 94 through the inlet passage 62 past the valve 66 into the cylinder member 14.

When the rod 48 is reciprocated by the lever away from the connector 32, a vacuum is drawn in the end of the tube 46 adjacent the connector 32 which has been vacated by the rod, the ball valve 66 seating sealingly on the seat 64. When the end of the rod 48 clears the hole 92 through the tube 46, hydraulic fluid from the reservoir 94 flows into said vacated space in the tube 46.Reciprocation of the rod 48 in the opposite direction pumps hydraulic fluid past the ball valve 66 into the interior of the piston and cylinder assembly 12, causing extension thereof, to telescope the piston 1 6 axially outwardly from the cylindrical member 1 4. Repeated reciprocation of the lever along the slot 60, causes successive amounts of hydraulic fluid to be pumped from the reservoir 94 in this fashion into the interior of the piston and cylinder assembly 12, thereby jacking up the load at 96 on the end of pipe 40 to the desired degree. It will be appreciated that, during this pumping, the ball valve 74 seats sealingly against its seat 72 to close the passage 70.

To release the jack 10, and to permit the piston 1 6 to telescope into the cylinder member 14, the relief screw 80 is screwed inwardly in the threaded outer portion of the countersink 78, until the probe 88 engages the ball valve 74, and unseats it from its seat 72. Hydraulic fluid under pressure can then flow from the interior of the piston and cylinder assembly 1 2 via the passages 62, 70 and 76, from the piston and cylinder assembly 1 2 directly into the reservoir 94. This permits the piston 1 6 to be retracted into the cylinder member 14.

In Fig. 2 reference numeral 110 generally designates a further piston and cylinder assembly in accordance with the invention. The assembly comprises a piston 11 2 and a cylinder member 114. The cylinder member 11 2 comprises an inner tubular portion 11 6 made of a smooth walled PVC pipe and a tubular outer reinforcing portion 11 8 made of steel pipe. The piston 11 2 in turn comprises a steel piston rod 120 and a piston head 122. The piston head comprises an annular steel disc 1 24 which is internally threaded and screwson to the end of the rod 1 20 inside the cylinder 114, said end of the rod 1 20 being correspondingly threaded.Two annular cup seals 1 26 are provided on opposite sides of the disc 1 24 facing away therefrom. An annular shoulder or flange 1 28 is provided on the rod 1 20 between the threaded end of the rod 1 20 and the remainder thereof. The shoulder 1 28 projects radially outwardly and extends circumferentially and the disc 1 24 and seals 1 26 are held tightly and sealingly up against the shoulder 1 28 by a pair of lock nuts 1 30.

The disc 1 24 acts as a rigid support for the seals 126, the seals facing away from said support.

Opposite ends of the pipe 11 8 are internally threaded and are provided with externally threaded plugs 132, 1 34. The plug 1 34 is annular and has an annular seal 1 36 which seals against the rod 1 20 which passes axially out of the cylinder member 114 via said plug 1 34. The outer end of the rod 1 20 is shown having an eye 138; and the pipe 11 8 is shown having a bracket 140 fast therewith on its outside at its end adjacent the plug 132, the bracket 140 having an eye 142.

The plugs 1 32 and 1 34 abut opposite ends of the PVC pipe 11 6 and locate it axially in position in the steel pipe 118. The plugs 132 and 1 34 respectively have passages 144 and 1 46 therethrough via which the interior of the cylinder 114 is placed in communication with respective high pressure hydraulic hoses 148 and 1 50 by means of pipe nipples 1 52.

In use said hoses 148 and 1 50 will be connected eg to a source of hydraulic working fluid under pressure, in the form of a hydraulic pump, which may be reversible, or may be provided with valves whereby it pumps reversibly, so that the pump feeds hydraulic liquid to one of the hoses 148, 150, while withdrawing hydraulic fluid from the other. A double acting piston and cylinder assembly 110 is thus provided, which can be extended or retracted by working liquid under pressure from the hydraulic pump.

The eyes 1 38 and 1 42 are connected to objects, such as the parts of a jack mechanism, which are to be moved relatively to one another by force from the piston and cylinder assembly.

With regard to Fig. 2 it will be appreciated that by omitting one of the cup seals 1 26 and one of the hoses 148, 150, the piston and cylinder assembly 110 can be made to be single acting instead of double acting. In this case the hose on the side of the disc 1 24 remote from the retained cup seal 1 26 will be omitted, the passage 80, 82 with which the omitted hose was associated merely acting as an air bleed passage.

A prime advantage of the invention is the simplicity of construction, with particular reference to the inexpensive materials of construction, and the simple and inexpensive maching operations which must be carried out to make the various metal parts of the piston and cylinder assembly. All the parts of the piston and cylinder assembly. All the parts of the piston and cylinder assembly other than the PVC pipe can be of mild steel, and the machining operations which have to be carried out to make the various metal parts can be essentially confined to drilling, tapping, welding, cutting and turning.

The most sophisticated parts of the invention which are subjected to wear are the seals 20 and 126, and it is a major advantage of the invention that the use of the PVC pipe, or some similar pipe such as glass fibre reinforced resin, forming the tubular portion 26, 11 6 combats such wear. The inner surface of said PVC pipe provides a smooth cylindrical surface against which the seals 20, 1 26 can seal, while moving axially along said PVC pipe, under considerable hydraulic pressure.

Were the PVC pipes to be omitted, and were the seals to act directly against the steel pipes 28, 118 constituting the reinforcing portions, the seals would be worn away relatively quickly. On the other hand, the PVC pipes 26, 116, by themselves, will be unable to withstand the internal hydraulic pressures encountered, the steel pipes 28, 11 8 consequently provide external support for the PVC pipes 26, 116, to enable them easily and inexpensively to resist such pressures. Piston and cylinder assemblies in accordance with the invention are thus provided, with the necessary strength and durability, in an extremely inexpensive and easily applied fashion, various seals which are readily available and the PVC piping, forming the only nonmetal parts. Indeed, stock PVC piping and steel piping can be used provided that the outer diameter of the PVC piping matches the inner diameter of the steel piping sufficiently closely, and the provision of the plugs which screw to opposite ends of the steel piping permits easy opening of the assembly, and replacement of any seals or PVC piping which become warn.

Claims

1. A telescopically extensible piston and cylinder assembly which comprises a piston axially reciprocable within a cylinder member, the cylinder member having an inner tubular portion of relatively weak material in sealing engagement with the piston, and an outer reinforcing portion of relatively strong material which surrounds the tubular portion and reinforces it against deformation or damage caused by fluid pressure in the inner tubular portion.

2. An assembly as claimed in claim 1, in which the tubular portion is of a plastics material and the reinforcing portion is of metal.

3. An assembly as claimed in claim 1, in which the plastics material is selected from the group consisting in polyvinyl chloride (PVC) and glass fibre reinforced resin, and the metal is steel.

4. An assembly as claimed in any one of the preceding claims in which the tubular portion is a pipe length and the reinforcing portion is also a pipe length, the tubular portion being receivable within the reinforcing portion with a sufficiently close fit to prevent fluid pressure in the tubular portion from expanding the tubular portion sufficiently to affect the sealing engagement between the piston and said tubular portion.

5. An assembly as claimed in claim 4, in which opposite ends of the reinforcing portion are closed off by closure members which engage opposite ends of the tubular portion to locate it axially in the reinforcing portion, at least one of the closure members having the piston passing sealingly therethrough, and at least one of the closure members having a passage therethrough for working fluid.

6. An assembly as claimed in claim 5, in which the closure members are plugs which are externally screw threaded and which screw into the ends of the reinforcing member, which are internally screw threaded.

7. An assembly as claimed in any one of the preceding claims, in which the piston is provided with at least one flexible cup seal for sealing engagement with the inside of the tubular member, the cup seal facing away from a rigid support therefor on the piston.

8. An assembly as claimed in any one of the preceding claims, which forms part of a jack.

9. A telescopic extensible piston and cylinder assembly, substantially as described and as illustrated herein.