GB2184657A

GB2184657A - Hypodermic syringe

Info

Publication number: GB2184657A
Application number: GB08531333A
Authority: GB
Inventors: Roger Hubert Morley; Richard Kitley Power
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-12-19
Filing date: 1985-12-19
Publication date: 1987-07-01
Also published as: GB8531333D0

Abstract

As shown in Figure 1, a pawl 30 is held displaced by a sleeve 34 located behind the piston 18. When the piston is retracted to draw liquid into the syringe the sleeve is displaced to the opposite end of the barrel where the pawl is then resiliently urged into the path of the piston. When the syringe is used to make an injection, the piston displaces the pawl to the inoperative condition as the piston passes the pawl, but then the pawl resiliently returns behind the piston, because the sleeve 34 is out of the way, and the pawl 30 then prevents the piston being withdrawn on a second occasion. This makes the syringe capable of use once only. <IMAGE>

Description

SPECIFICATION Hypodermic syringe This invention relates to a hypodermic syringe.

The object of the invention is to provide a disposable syringeforonce only use.

According to the invention a disposable hypodermic syringe comprises a barrel, a needle located at one end of the barrel, a piston in the barrel, and a piston rod projecting from the opposite end of the barrel, and is characterised by the provision of non-return means effective between the relatively moveable parts allowing a single cycle of operations only and preventing a second cycle of operations.

The non return means may comprise a rachel or pawl mechanism held in an inoperative position priorto a first operational cycle, and displaced to an operational condition during that cycle so asto be effective subsequently.

The invention is more particularly described with reference to the accompanying somewhat diagrammatic drawing wherein Figure 1 is a sectional elevation, on an enlarged scale, of an embodiment ofthe invention in one position; and Figure2 is a similarview of the same in a second position.

Referring now to the drawing, the syringe illustrated is conventional in having a generally tubular body 10 closed by an end wall 12 to which needle 14 is attached at one end ofthe body, and by a cap 16 at the opposite end ofthe body. These parts 10-16form a barrel assembly.

Piston 18 is attached to piston rod 20 which extendsthroughthe body and terminates in an enlarged end 22 for manual retraction/displacement ofthe piston assembly relative to the barrel assembly.

In ordinary use,the needle 14 is inserted for example into an ampoule ofthe drug to be dispensed, the piston 18 is retracted from the illustrated position towardsthe end 16to draw liquid into the barrel, the piston is returned for a small distance to expel air, and then the injection is made returning the piston to the illustrated position as the barrel contents are expressed.

The syringe ofthe invention, in this embodiment, has two additional components namely, a pawl 30 which is disposed in a chamber32 opening from the barrel neartheend 12, and a sleeve 34.

Figure 2 shows the pawl 30 in its extended position. In this position it substantially prevents movement of the piston in the direction necessaryto draw liquid into the syringe.

Figure 1 shows the sleeve 34 located adjacent to the needle and holding the pawl in a displaced condition. Figure 1 shows the position of the syringe according to the invention ready for use. In this position, the piston can be retracted to draw liquid into the syringe because the sleeve 34 holds the pawl retracted. The pawl is only freed for displacement to the Figure 2 position after the piston has moved past the pawl. The sleeve is moved by the piston, and terminates its movement adjacent the cap 16 shown in Figure 2.

When the piston is returned to make the injection by expressing liquid from the barrel, the piston can displace the pawl backtowardsthe Figure 1 position but it then snaps behind the piston as the parts reach the Figure 2 position.

Hence the syringe can be used once, and once only, because any attempt to use it a second time results in the pawl 30 blocking the path of the piston.

In this embodiment shown in the drawings,the pawl may be moulded integrally with the barrel from a suitable plastics material, or possibly made in a separate operation and moulded in when the barrel is made. The movement of the pawl from the Figure 1 to Figure 2 position is intended to be due to the inherent resilience ofthe material, but it is possible for example to arrange that it is the wall of the barrel orchamberwhich is deformed at the root ofthe pawl during this operation.

The strength of the pawl is preferably such that any attempt to force the piston past the pawl in an attempt to re-use the syringe, will result in the syringe being rendered useless, for example bythe piston being pulled off the piston rod 20, or by the pawl rupturing the wall of the barrel. Thus, the pawl and the wall of the barrel may be arranged so that the pawl is freely moveable between the positions shown in Figures 1 and 2 and is resiliently urged to the Figure 2 position, but any attempt to continue the effectively clockwise movement of the pawl (in the drawing)aboutitsrootcausesthechambertotearat its junction with the barrel proper.

The invention is not limited to the use of a pawl, or to the use of a pawl in the illustrated position. It may be preferable to provide the non-return means such as the pawl on the piston rod for co-operation with a formation provided on the cap 16, in the interests of more convenient moulding ofthe parts in manufacture.

Claims

1. According to the invention a disposable hypodermic syringe comprises a barrel, a needle located at one end of the barrel, a piston in the barrel, and a piston rod projecting from the opposite end of the barrel, and is characterised by the provision of non-return means effective between the relatively moveable parts allowing a single cycle of operations only a preventing a second cycle of operations.

2. A disposable syringe as claimed in Claim 1 wherein a pawl provided on one of the relatively removable parts is held in an ineffective position during a part of a first cycle of operation in use ofthe syringe, and is freed during that cycle so asto project into the path of movement of the parts.

3. A disposable syringe as claimed in Claim 2 wherein the pawl is arranged to be displaced backto an ineffective position during a later part of the said first cycle of operation and then snap engages to a position permanently blocking movement and so preventing a second cycle of operations.

4. A disposable syringe as claimed in Claim 2 or Claim 3 wherein means are provided for holding the pawl in the ineffective position which are displaced by the piston assembly.

5. A disposable syringe as claimed in Claim 1 wherein the non return means are effective between the piston rod and the barrel.

6. A disposable syringe as claimed in Claim 1 wherein the non return means are effective in the vicinity of the opposite end of the barrel to the needle.

7. A disposable syringe as described and/or illustrated in the drawings.