GB2190962A - Lifting jacks - Google Patents

Abstract

A jack having an elongatable jack body comprising a pair of telescopically mutually slidable members (2,4) forming a housing, a fluid pressure ram positioned within the housing such as to force elongation of the jack body in use, and a locking fork (8) having arms (9) positionable in holes (7) in member (4) to engage the member (2) to form a mechanical barrier against shortening of the jack body. The jack can be operated front the hydraulic fluid system of a tractor. <IMAGE>

Description

SPECIFICATION Lifting jacks The present invention relates to lifting jacks.

It is known to provide lifting jacks in which a hydraulic or pneumatic ram is employed to provide the lifting action. Generally, a telescopically slidable member of the hydraulic ram will be exposed in use. Where such jacks are to be used in conditions where they will be exposed to contamination by dirt or by corrosive chemicals, this is likely to lead to failure of the jack due to ingress of dirt or corroding materials into the seals of the ram.

Jacks incorporating such hydraulic and pneumatic rams generally require the maintenance of hydraulic or pneumatic pressure in order to keep the ram extended against a load.

It has been proposed to provide a hydraulic jack comprising a hydraulic ram having an inner and an outer telescopically slidable part, the inner such part being welded at its free end to a base plate member to which is also welded a square-section tubular member which surrounds the inner telescopically slidable member of the ram. The tubular member is provided with holes in which a locking fork may be received passing around the inner slidable member of the ram. The space between the legs of the locking fork is insufficient to accommodate the outer slidable member of the ram which in use is uppermost. Accordingly, the tubular member provides some degree of protection for the ram and also provides, in conjunction with the locking fork, a means for supporting the ram in an extended position without the use of hydraulic pressure.

Accordingly, the ram may be extended by use of hydraulic pressure, locked in an extended position and disconnected from the hydraulic supply.

Such a device fails to provide the best shielding of the ram from contamination because only one half of the ram is enclosed within a protective member. Also, the full weight of any load applied to the jack is carried on the locking fork, once the hydraulic supply has been disconnected. The locking fork comprises a pair of arms each of which passes through a pair of aligned bores in opposed walls of the tubular member. The weight of the load is transmitted by the outer telescopi cally slidable member of the ram onto those portions of the arms lying inside the tubular member between the opposed bores. There is therefore a danger that an excessive load may bend the arms of the fork making it impossible to remove the fork from the tubular member. In an extreme case, the arms of the fork might give way.

The present invention provides a jack comprising an elongatable jack body comprising a pair of telescopically mutually slidable members forming a housing, a fluid pressure ram positioned within the housing such as to force elongation of the jack body in use, and a locking device positionable to engage the said telescopically slidable members to form a mechanical barrier against shortening of the jack body.

Preferably, the jack comprises a base for ground engagement bearing a first of the said telescopically slidable members.

Preferably the second of the said telescopi cally slidable members slides within the first said telescopically slidable member.

Preferably, one of said pair of telescopically slidable members is provided with a plurality of holes spaced lengthwise of the jack body and passing through a wall of the said member in which a portion of the locking member is receivable to block shortening of the jack body.

The locking member may in such a case be a locking pin.

Preferably however, said one telescopically slidable member is provided with a plurality of pairs of adjacent through holes, said pairs being spaced lengthwise of the jack body. The locking member may then suitably be a fork having a pair of generally parallel arms.

Preferably, the said one member is provided with a further plurality of holes passing through a wall of the said member, each hole of said further plurality being disposed opposite to and in alignment with a corresponding hole in the first mentioned plurality of holes.

The locking pin or locking fork arms may pass through aligned holes of the first plurality and the second plurality provided in respective opposite walls of the slidable member.

It is advantageous if both sets of holes are through bores. However, it is possible to operate such a jack if at each level lengthwise along the jack body there is provided at least one through bore facing a blind bore open to the interior of the telescopically slidable member so that the locking pin or arm of the locking fork can be passed through the through bore to locate in the blind bore.

Preferably, an extension member is provided adapted to be connected to the end of the jack member opposite the base to provide an extension of the length of the jack body.

This may be connected to the jack body by use of a similar locking pin or locking fork as described above and may comprise depending wall members containing aligned bores for alignment with bores of the telescopically slidable member to receive the locking pin or fork of the extension.

Preferably, the jack comprises an inlet/outlet connection for pressurising fluid. This is preferably situated adjacent the base of the jack.

Preferably, the actuating ram is a hydraulic ram.

Preferably, such a ram is of metal construction and preferably the housing members are also of metal construction, the ram being fixed, eg by welding, within the housing.

In an alternative embodiment, the ram may be a pneumatic ram.

The ram may be provided with manually operable means for pressurising the ram such as a hydraulic fluid pump or a pneumatic pump.

The invention will be further illustrated by the following description of a preferred embodiment thereof with reference to the accompanying drawings in which Figure 1 is a perspective view of a jack according to the invention; Figure 2 is a perspective view of a hydraulic ram contained within the jack of Figure 1; Figure 3 is a perspective view of an extension piece for fitting to the upper part of the jack of Figure 1.

As shown in Figure 1, a jack comprises a base member 1 having welded thereto a square-section tubular member 2 having an inverted U-shaped aperture 3 at its lower end at which it is welded to the base member 1.

Received within the tubular member 2 is a smaller tubular member 4 which is telescopically slidable within tubular member 2 and defines a housing. Tubular member 4 is provided at its upper end with a closure wall 5 and a pair of outwardly flared load gripping wall members 6. In each of two opposed faces of the tubular member 4 are provided a pair of parallel spaced rows of through bores 7 arranged as adjacent pairs of bores on each of the two opposed faces. A locking fork 8 having a pair of parallel spaced arms 9 is provided attached to the jack by a chain 10. The arms 9 are sized to be received within any pair of bores 7 and to pass through such bores 7 on one side of the jack and out through an aligned pair of bores 7 in the opposite face of the tubular member 4.

A hydraulic ram 11 shown in Figure 2 of conventional design is received within the housing of the jack of Figure 1 and is welded to the base member 1 and to the closure wall 5 at its lower and upper ends. The hydraulic ram 11 is provided with a connector 12 for connection to a hydraulic fluid pressurised supply line, suitably by means of a quick release fitting.

Preferably, the connector 12 incorporates a check valve which serves to prevent leakage of hydraulic fluid from the ram 11 once the connector is disconnected.

As shown in Figure 3, there is provided an extension piece for fitting to the top of the jack as shown in Figure 1. The extension piece comprises a tubular wall member 13 of similar cross sectional dimensions to tubular member 4. At its upper end, the extension 13 is provided with a pair of load gripping outwardly flared wall members 14 similar to wall members 6 of the tubular member 4. At its lower end, the extension 13 is provided with a pair of depending wall members 15 each provided with a pair of through bores 16, the pairs being in alignment.

In use, wall members 15 may be slid over the saddle formed at the top of the tubular member 4 by the load gripping wall members 6 so as to bring the bores 16 into alignment with the uppermost pair of bores 7 of the tubular member 4. A locking fork 17 similar to locking fork 8 is provided attached to the extension by a chain and can be used to secure the extension in place.

It will be noted that the weight of the load applied to the jack is carried by the locking fork 8 once the hydraulic connection 12 is disconnected. However, because of the design of the housing, the weight of the load is carried on widely spaced regions of the arms 9 of the fork. The arms are trapped between the bores 7 in which they are located and the upper edge of the tubular member 2. There is therefore little tendency for the arms to be deformed by bearing the load.

The jack may be used in conjunction with a hydraulic supply such as that of a tractor and is likely to be particularly useful in agricultural work. The jack may for instance be employed in changing tractor and trailer wheels on a farm at any location, or for raising a tractor to enable settings of the tractor machinery to be altered.

The jacks may be used as axle stands or parking jacks by using the locking bar and disconnecting the hydraulic supply once the jacks are in position.

Whilst the invention has been described with reference to particular characteristics of the specific embodiment, it will be appreciated that many variations and modificiations of this embodiment are possible within the scope of the invention.

Claims (9)

1. A jack comprising an elongatable jack body comprising a pair of telescopiclly mutually slideable members forming a housing, a fluid pressure ram positioned within the housing such as to force elongation of the jack body in use, and a locking device positionable to engage the said telescopically slidable members to form a mechanical barrier against shortening of the jack body.

2. A jack as claimed in Claim 1, comprising a base for ground engagement bearing a first of the said telescopically slideable members.

3. A jack as claimed in Claim 1 or Claim 2, wherein one of said pair of telescopically slidable members is provided with a plurality of holes spaced lengthwise of the jack body and passing through a wall of the said member in which a portion of the locking member is receivable to block shortening of the jack body.

4. A jack as claimed in Claim 3, wherein said one telescopically slidable member is provided with a plurality of pairs of adjacent through holes, said pairs being spaced length wise of the jack body.

5. A jack as claimed in Claim 3 or Claim 4, wherein the said one member is provided with a further plurality of holes passing through a wall of the said member, each hole of said further plurality being disposed opposite to and in alignment with a corresponding hole in the first mentioned plurality of holes.

6. A jack as claimed in any preceding claim, including an extension member adapted to be connected to the end of the jack member opposite the base to provide an extension of the length of the jack body.

7. A jack as claimed in Claim 6, wherein the extension member comprises depending wall members.

8. A jack as claimed in any preceding claim, which comprises an inlet/outlet connection for pressurising fluid.

9. A jack as claimed in any preceding claim, wherein the actuating ram is a hydraulic ram.