GB2184191A - Plungers - Google Patents

Abstract

A plunger (5) is adapted for detachably holding rigidly together two lengths of tubing (1 and 3). The plunger (5) comprises two part-cylindrical members (8) adapted to fit face to face to form a cylinder of diameter just less than the internal diameter of the tubing so that it can slide easily within said tubing. The members (8) are held together in said cylindrical disposition by resilient means (10). The members (8) may be forced apart against the resilient holding means by such means as a bolt (11) until said plunger forms a tight fit against sides of said tubing. It thereby fixedly engages the two lengths of tubing together. The tubing (1), which may form a handle 2 of a wheelchair or pram, may be pivotted (4) to the tubing (3). <IMAGE>

Description

SPECIFICATION Plungers The present invention relates to plungers, particularly of the type used to connect together two lengths of tubing.

In general, such plungers occupy substantially the entire internal area ofthetubing and can be moved from a position wherethey bridgethe join to a second position where the plunger is substantially entirely within one length of tubing. In this second position the two lengths of tubing can then be separated or bent. It is generally preferred that the length oftubing which accepts the plunger is, in use, u ppe rm ost so that a positive action is required to separatethetwo lengths. when they are subsequently placed in alignment, the plungerfalls underthe influence of gravity to connect them together.

Plungers ofthistype are commonly used infolding articles such as wheelchairs or prams which require to be folded for ease of transport. In the case of wheelchairs, it may be necessary to have parts which fold easily, when the occupier wishes to take part in a sporting activity or when he requires to be lifted from behind. One part which commonly folds in wheelchairs is a back resttowhich is attached the handles by which the wheelchair is pushed. The invention will be described with particular reference to this utilisation although, as stated above, other uses are possible.

As stated above, it is common to hingetogether two lengths of tubing to form a back frame for a wheelchair. The handles are attached to the upper of these lengths of tubing. Great force may have to be transmitted through such a joint, for example, when the wheelchair is tilted backwards to be lifted up a kerb. Accordingly, the joint must be strong. Clearly, in order to be easily operable, the plunger must be an easy sliding fit within the tubing so that it can be disengaged undue effort. However, it has been found that the forces exerted on this joint cause the plunger to damagethe lower section ofthetubing at a pointoppositethe hinge.This is generallythought to be because the plunger is a loose fit and because the hinges are so arranged thatthe usual force on the handles, downwardly, causes the plungerto knock against the internal surface ofthe lowertubeand eventually cause bulging and possibly fracture at that point.

It is the object of the present invention to provide a plungerwhich will overcome the above disadvantage and which may have other useful applications.

According to the present invention there is provided a plungerfor detachably holding rigidly together two lengths oftubing, the plunger comprising two part-cylindrical members adapted to fit face to face to form a cylinder of diameter just less than the internal diameter of the tubing to be able to slide easilywithin said tubing, resilient meansto hold said members in said cylindrical disposition, and meanstoforceapartsaid membersagainstthe resiliant holding means until said plungerforms a tightfitagainstsidesofsaidtubing.

Preferably each of the members comprises an axially extending half of the cylinder.

The resilient holding means may comprise one or more elastomeric rings extending in a respective one or more grooves around an outer circumference of the members when they are assembled together.

One end of each member may be so tapered that the assembled plunger has a substantially hemispherical end.

The forcing means may be a screwthreaded bolt extending through a correspondingly screw threaded through-hole in one memberto engage the contiguous surface ofthe other.

Preferably said surface is provided with a blind hole aligned with the through hole.

The bolt may extend through a slotin thetubing wall to beturnedforseparatingthemembers.The bolt may also constitute means by which the plunger is causedto slidewithin thetubing at least in one direction.

The lengths oftubing advantageously are hinged togetherand maycomprise partofaframeofa wheelchair, pram or other folding article.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: Figure 1. shows schematically part of a wheelchair frame including a plunger embodying the invention; Figure 2. a side elevation of a plunger embodying the invention; Figure3. is a view from one end of a plunger embodying the invention in separated condition; and Figure 4. is a cross-sectional view of a plunger in separated condition.

Referring now to the drawings, and particularly Figure 1,there is shown a portion of a backframefor a wheelchair comprising a handle section 1, bent at one end to receive handles 2 and a main section 3.

The two sections are hinged together by means of hinge4. In orderto hold the two sections rigidly togetherthere is provided a plunger 5 able to slide within the tubing. The upper section 1 has a slot 6 in one wall through which a handle 7 of the plunger protrudes. By this means, the plunger 5 can be lifted upwardly so that it is entirely within the upper section 1, whereafter the two sections can be hingedly separated.

When the sections are again aligned,the plunger5 should slide down underthe force of gravity to re-engage the sections. Forthis purpose, the lower end ofthe plunger5 is generally rounded to aid locating itself within the lower section 3.

Referring now to the more detailed view ofthe plunger shown in Figures 2 to 4, it can be seen that the plunger comprises a cylinderformed of two longitudinal halves. These longitudinal members8 may bethe same length ordifferent,for example 55 or75 millimetres. Each member8 has two grooves9 extending around its curved circumferential surface.

The grooves 9 are each dimensioned to accomodate an O-ring 10 of resilient material such as nitride rubber, for example 1.78 millimetresthickand 17.2 millimetres outside diameter. Once the two halves of the plunger are assembled together, they may be held in such condition by means of these O-rings 10.

The handle 7 by means of which the plunger is moved upwardly in the tubing, is connected to the plunger 5 by means of a screwthreaded bolt 11 engaging in a correspondingly screwthreaded hole 12 in one of the members 8. The other member 8 has a corresponding blind hole on its flat surface, against which the bolt 11 may bear.

In order to use the plunger embodying the invention, it is first slid downwardly, either by gravity or by use ofthe handle7 until itis in a locking disposition. The bolt 11 is then turned so that the one member8which is inscrewthreaded engagement therewith will move away from the other member 8 against which the bolt bears. The O-rings 10 will expand to allow this moving apart but are sufficiently resilient that once the bolt 11 is unscrewed, they will act to draw tog ether the two members 8. The expansion ofthe plunger causes each member8to contact corresponding portion of the internal wall of the tubing and be fixedly held there until the bolt 11 is unscrewed. Since the plunger is nowfixedly engaged the two sections oftubing are more securely eonnected and there is less danger of damage to one section because of repeated pressure byan end of a comparatively loosefitting plunger.

Use of a plunger embodying the invention also enables a single plungerto be used fortubing of quite different internal diameters.

The preferred material for the plunger is mild steel or SG iron, finished with a brightzine plating.The plunger may easily be manufactured byturning a bar of material, cutting in half, and forming the blind hole in each half, one of which is later drilled through and tapped. Assembly is quite straightforward.

Claims (10)

1. Aplungerfordetachablyholding rigidly together two lengths of tubing, the plunger comprising two part-cylindrical members adapted to fit face to face to form a cylinder of diameter just less than the internal diameter of the tubing to be able to slide easily within said tubing, resilient means to hoid said members in said cylindrical disposition, and means to force apart said members againstthe resilient holding means until said plunger forms a tight fit against sides of said tubing.

2. Aplungerasclaimed in claim 1 ,wherein each ofthe members comprises an axially extending half of the cylinder.

3. A plunger as claimed in either claim 1 orclaim 2, wherein the resilient holding means comprises one or more elastomeric rings extending in a respective one or more grooves around an outer circumference of the members when they are assembled together.

4. A plunger as claimed in any one ofthe preceding claims, wherein one end of each member is so tapered that the assembled plunger has a substantially hemispherical end.

is. A plunger as claimed in any one of the preceding claims, wherein the forcing means is a screw-threaded bolt extending through a correspondingly screw-threaded through-hole in one memberto bear against the contiguous surface of the other.

6. A plunger as claimed in claim 5, wherein said contiguous surface is provided with a blind hole aligned with the through hole.

7. A plunger as claimed in eitherclaim 5 or claim 6, wherein the bolt extends through a slot in the tubing wall to be turned for separating the members.

8. A plunger as claimed in claim 7, wherein the bolt constitutes means by which the plunger is caused to slide within the tubing at least in one direction.

9. A plunger as claimed in any one ofthe preceding claims, wherein the lengths oftubing are hinged together and comprise parfofaframeofa wheel chair, pram or other folding article.

10. Aplungerfordetachablyholding rigidly togethertwo lengths of tubing substantially as herein described with reference to the accompanying drawings.