US2419401A - Syringe plunger seal - Google Patents

Description

April 22, 1947 w. H N 2,419,401

SYRINGE PLUNGER SEAL Filed Feb. 25, 1946 l a Fig. I

F'l'g. 2 .F'ig.3

Dr. William E. Hinds INVENTOR ATTORNEY Patented Apr. 22, 1947 UNITED STATES PATENT OFFICE.

SYBINGE PLUNGER SEAL William E. Hinds, Hillsboro, Oreg.

Application February 25, 1946, Serial No. 650,107

4 Claims.

The present invention relates to improved syringes and particularly to a plunger seal attachment adapted for use with commercially available injection syringes.

The most commonly used hypodermic injection syringe comprises a glass barrel and a glass plunger, the inner cylindrical surface of the barrel and the outer cylindrical surface of the plunger of each syringe being ground and mated with high degree of accuracy to assure a close fit between the barrel and plunger. Glass is a preferred material for the manufacture of syringes since it is easily formed, readily sterilized and permits inspection of the contents of the syringe so that the operator can be certain that the injection is not contaminated by any foreign matter, air bubbles and the like which would interfere with the operation of the syringe or be injurious to the patient. However, even when the barrel and plunger are ground to obtain the closest sliding fit, more or less leakage of the contents of the syringe takes place between these two parts as the plunger is pushed in. This is particularly true when the injections are made at a slow rate. For example when the rate is of the order of 1 to 2 cc. per hour for a 20 cc. syringe, the liquid may seep past the plunger at such a rate that none of the liquid is actually injected into the patient.

Another disadvantage of glass syringes is that the glass parts thereof are easily broken. Since the plunger and barrel of each syringe are matched during grinding thereof by the manufacturer, the plungers of two difierent syringes of the same type cannot be satisfactorily interchanged to obtain a leak-proof fit, so that when either the barrel or plunger is broken, both must be discarded.

A primary object of the present invention is to provide a simple, inexpensive attachment for such syringes, which attachment will effectively prevent leakage of the injection past the plunger irrespective of the rate at which the injection is being administered.

Another object of the invention is to provide a plunger seal for a syringe so constructed that it can be securely attached to the plunger and easily removed therefrom to facilitate sterilization of the attachment and the various parts of the syringe.

A further object of the invention is to provide an attachment for existing syringes which will permit a greater clearance between the plunger and barrel thereof and the interchanging of plungers of varying diameters.

These and further objects of the invention will become apparent from the following descrip-- tion when taken in connection with the accompanying drawing in which:

Fig. 1 is a view, partially in section, of a standard glass hypodermic syringe provided with the attachment of the present invention; Fig. 2 is an enlarged cross-sectional view of the attachment; and Fig. 3 illustrates a modified form of the attachment.

Referring to Fig. 1 of the drawing, I is the glass barrel of a standard hypodermic syringe having at one end thereof a nipple 2 adapted for connection of a hypodermic needle (not shown). The other end of the barrel is open to receive a cylindrical glass plunger 3 having a knob or handle 4 at one end, the inner end 5 of the Plunger being formed substantially flat and at right angles to the longitudinal axis of the plunger. The inner cylindrical surface of the barrel and that portion outer cylindrical surface of the plunger which comes in contact with the barrel during use of the syringe are ground to obtain a close, slidable fit between the two parts, the manufacturing cost of the syringes varying directly with the degree of accuracy with which the barrel and plunger are ground and mated.

The above mentioned elements comprise the principal parts of a standard glass syringe. Such syringes are particularly acceptable to the medical profession because their simple design, involving no crevices, joints or threaded connections, makes them easy to use and greatly facilitates the cleaning and sterilization thereof.

It will be noted that the closer the lit between the ground surfaces of the barrel and plunger, the less likelihood there is of substantial leakage of the contents of the syringe between these surfaces. On the other hand a close fit also means greater friction between these two elements and greater possibility of breakage during assembly and use of the syringe. Hence for practical purposes, there is a limit on the closeness with which the two elements can be fitted since they must be so constructed as to permit repeated disassembly for cleaning and sterilization purposes.

Depending on the degree of accuracy with Which the plunger and barrel are mated, more or less leakage takes place therebetween when the plunger is pushed in during injection of a medicant, particularly when the rate of injection is low. In accordance with the present invention I have provided an attachment. for existing syringes which is designed to eliminate completely the difficulty of leakage between the plunger and barrel of such devices. The attachment 6 which is designed to be readily attached to and detached from the forward end of the plunger is shown in greater detail in the enlarged cross-sectional view of Fig. 2 as comprising a disc I having a suction cup 8 integrally formed with one side of the disc. The disc and cup are made of a non-toxic elastomeric material such as rubber, neoprene, or the like, natural rubber being preferred for most applications. The circumference of the disc is slightly larger than the internal diameter of the barrel 1 so that a'close fit is obtained therebetween. The suction cup 8 detachably holds the attachment tightly onto the end of the plunger 3. On removal of the plunger from the barrel, the attachment 6 can be readily slipped laterally from the end of the plunger.

It will be apparent that I have provided a leakproof seal for use in standard syringes which is of simple construction and easy to clean and sterilize in that it contains no crevices, cavities or other surface irregularities, It is readily attachable and detachable from the end of the syringe plunger and can be cleaned and sterilized along with the remaining parts of the syringe,

I am aware that various syringes have previously been proposed having rubber plungers or plunger tips to prevent leakage of the injection between the plunger and the barrel. However, in these prior devices the rubber member was either not attached or attachable to the plunger member as in. those cases where the rubber member forms part or all of the closure plug for an ampoule adapted to be inserted into a syringe or the rubber members were permanently or semipermanently attached to the plungers so that they were difficult to clean and sterilize and when once removed from the plunger member for such purposes were even more difficult to replace. The attachment of the present invention differs markedly from the prior art devices in the ease with which it can be attached to the plunger. For example, after the syringe has been disassembled and the various parts thereof sterilized the whole can be reassembled without touching any parts of the syringe which come in contact with the medicant. This can be done by picking up the plunger by means of the knob 5, using the forward end of the plunger to expose the suction cup portion of the seal and touching the flattened forward end of the plunger to the suction cup with a pressure sufficient merely to obtain some adhesion between these two parts; At this point the disc E need not be centered with respect to the longitudinal aXis of the plunger. The disc portion of the attachment is then inserted into the barrel i. If necessary the attachment can then be centered with reference to the plunger by suitably moving the plunger into line with respect to the barrel after which both the plunger and attachment can be inserted intothe barrel.

The modification shown in Fig. 3 is adapted to provide a more positive wiping action of the edge of the disc portion of the attachment with the sides of the barrel. In this modification, the disc portion comprises a main front portion l I of a size adapted to provide a close fit with the syringe barrel and a backing portion i2 of a diameter somewhat less than the diameter of mainportion I i but sufiiciently large to-reinforce the main portion without contacting the inner surfaces of'the syringe barrel. Suction cup I 3 is integrally formed on the backing portion of the disc, neck- 4 [4 being as large as possible without interfering with the suction action of cup l3.

As has been previously indicated my seal can be employed not only for leak-proofing the standard glass syringes but also for reclaiming unbroken parts of such syringes.

In any given type and'make of syringe it has been found that there is only a very small variation in the diameters of the barrels, Although these variations are sufiicient to cause substantial leakage particularly when the smallest plunger of a given line of syringes is inserted into one of the larger barrels, the differences in diameter are not so great that an attachment of the type herein disclosed having a disc diameter slightly larger than the smallest barrel opening cannot satisfactorily be employed with any syringe of the same type and make. Thu by means of my attachment, an unmated barrel and plunger can be reclaimed provided the plunger can be slidably inserted into the barrel.

The attachments of the present invention are particularly adapted for use with syringes having a barrel diameter of about one inch or less. With such attachments the thickness of the disc portion will ordinarily be from one-fourth to oneseventh the diameter of the disc while the neck 9 connecting the vacuum cup to the disc should have a diameter at least equal to one-half that of the disc and preferably should be as large as possible. As is also shown in Fig. 2 of the drawing the vacuum cup should have a diameter of at least about three-fourths that of the disc and ispreferably made as shallow and flexible as possible since only a minimum amount of suction is necessary to assure satisfactory adherence of the attachment to the plunger head.

While the invention has been described with reference to the use of the seal in combination with glass syringes, it is not restricted thereto since the sealing attachment can also be employed for leak-proofing metal or combination metal and glass syringes comprising a plunger having a fiat forward end to which the attachment can be secured by means of the suction cup.

Having decribed the invention in what are considered to be preferred embodiments thereof it is desired that it be understood that the specific details shown are merely illustrative and that the invention may be carried out by other means.

What I claim is:

l. A plunger attachment for preventing leakage between the plunger and barrel of a syringe, said attachment comprising a resilient discshaped member and a suction cup integrally formed therewith and adapted for holding said attachment on the forward end of the plunger.

2. A syringe plunger seal adapted to be detachably held on the forward end of a syringe plunger, said seal comprising a resilient discshaped member having integrally united therewith a resilient suction. cup adapted to hold said seal in operating position on the end of said plunger.

3. A rubber attachment adapted to prevent leakage between the ground, slidably engagingv surf-aces ofthe plunger and barrel of a glasssyringe, said attachment comprising arubber disc having a diameter slightl larger than the inter-- nal diameter of the syringe barrel and a shallow suction cup integrally formed with one .side of said disc and connected thereto'over at least onehalf the diameter of the disc, saiddischaving a thickness from about one-fourth to one-seventh: the diameter thereof, the said suctioncuphaving,

a diameter about three-fourths the diameter of with the inner cylindrical surface of said barrel, and a resilient seal detachably mounted on the forward end of said plunger, said seal comprising a disc having a diameter slightly larger than the internal diameter of the barrel and a suction cup integrally formed with said disc for. detachably securing said seal to said plunger.

WILLIAM E. HINDS.

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