Syringe Plunger Head

Abstract

Syringe apparatus having a plunger head with a peripherally grooved flange urged against the interior wall of the syringe by a resilient O-ring wedged in an annular groove in the head.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to syringes and relates more particularly to plungers of precise measuring devices or syringes which are used to inject minute samples in gas chromatography, for delicate medical injections, in treatment of small animals, and for a variety of similar projects in chemical and medical research laboratories.

2. Description of the Prior Art

There are various types of plunger heads for syringes used in chromatographic work and the like but there has been a problem in some types of such syringes of keeping tight sealing engagement of the plunger head with the inner wall of the syringe bore so that relatively high pressures may be developed by the syringe without leakage.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises a plunger head for precise measuring syringes having a tubular or hollow barrel, and a plunger which carries the plunger head.

The present plunger head includes a cylindrical body from the forward end of which extends a reduced diameter part. There is an annular flange on the reduced diameter part of the head, the periphery of the flange slidingly and sealingly engaging the interior bore of the syringe barrel. The flange is thinner at the base where it joins the reduced diameter part and the head has an annular, outwardly opening groove at the inner side of the open end so that said groove is narrower at the bottom than at the top. A resilient or elastic O-ring is tightly wedged in the groove and urges the flange forwardly to increase the sealing pressure of the periphery of the flange against the wall of the bore of the barrel. The O-ring itself does not engage the barrel but exerts a pressure on the flange such that it urges the free peripheral part of the flange forwardly and this in turn increases the pressure of the flange on the wall of the barrel bore.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a syringe plunger head having a highly effective sealing relation with the wall of the bore of the syringe barrel.

It is another object of the invention to provide a plunger head having a flange the periphery of which engages the wall of the bore of the syringe barrel and there is an O-ring providing pressure to increase the pressure of the flange on the wall of the syringe barrel bore.

The characteristics and advantages of the invention are further sufficiently referred to in connection with the following detailed description of the accompanying drawings which represent certain embodiments. After considering these examples skilled persons will understand that many variations may be made without departing from the principles disclosed and I contemplate the employment of any structures, arrangements or modes of operation that are properly within the scope of the appended claims.

Referring to the drawings, which are for illustrative purposes only:

FIG. 1 is a longitudinal sectional view of a portion of a syringe barrel with a side view of the plunger head embodying the present invention operably anchored to and supported by the syringe plunger;

FIG. 2 is an enlarged longitudinal sectional view of the plunger head carried by said plunger; and

FIG. 3 is a longitudinal sectional view showing an alternative arrangement of the forward end of the plunger head.

Referring more particularly to the drawings, there is shown a syringe barrel, indicated generally at 10, with a plunger member indicated generally at 12, operably disposed therein and having a plunger head, indicated generally at 14, anchored to the forward end of the plunger and supported by said plunger.

The syringe barrel 10 is of the usual well-known type and of any suitable material such as glass of suitable quality, for example. The barrel 10 has a cylindrical wall 16 defining a bore 18 which is closed at the forward end by an end wall 20 from which a tip 22 of well known character extends forwardly, there being a fluid passage 24 extending longitudinally from the forward free end of the tip into the bore of the barrel. The barrel is provided at the other end with a conventional flange, not shown.

The plunger head 14 is of any suitable material. A plastic material such as Teflon, for example, has been found to be very satisfactory, Teflon being Du Pont's registered trademark for its fluorocarbon resins, including the TFE (tetrafluoroethylene) resins.

Plunger head 14 comprises a cylindrical body 28 from the forward end of which a reduced diameter part 30 axially extends, The exposed annular wall 32 of the forward end of the body is inclined inwardly and forwardly.

On the reduced diameter part 30 and spaced forwardly of said forward end wall of the body is an annular radially extending flange, indicated generally at 36, of somewhat greater diameter than that of the body 28. Flange 36 has a peripheral portion the peripheral surface of which has a plurality of external grooves 40 separating a plurality of lands 42 the surfaces of which engage the interior wall surface of the barrel bore.

At its base, where it joins the reduced diameter part 30 of the plunger head, the flange is thinner, there being sidewall parts 44 and 46 at the rear side and the front side respectively that taper or are inclined inwardly toward each other, as best shown in FIGS. 2 and 3. The base of the flange 36 is to be considered the region where the flange joins the reduced diameter part and is indicated at 48. From FIGS. 2 and 3 it will be apparent that in cross section the flange is somewhat wedge shaped and that it will flex in an annular pivotal area at the base.

The walls 32 and 44 of the body 28 and flange 36 respectively are inclined forwardly and inwardly to define the sidewalls of a groove 50 at the rear side of the flange 36, with the wall 32 of the body inclined forwardly at a greater angle relative to the axis of the head than the forward inclination of the wall 44 so that the bottom of the groove 50 is narrower than the width of the open top of the groove.

Within the groove 50 is a resilient O-ring 52 of suitable material. For example, the O-ring may be of neoprene, or of Teflon, or Parker O-rings (Viton O-rings, Viton being the trademark of Parker Seal Co., 10567 W. Jefferson, City of Commerce, California).

The O-ring 52 is wedged in the groove 50 so that it exerts pressure against the flange 36 urging said flange forwardly and causing said flange to flex forwardly in the annular pivotal area at the base thereof. Thus the O-ring exerts pressure against the flange which in turn causes the flange, and particularly the lands 42 thereof, to be pressed tightly against the interior wall of the syringe barrel. This pressure of the O-ring on the flange effects a tilting thereof and greatly increases the effective sealing engagement of the flange with the interior wall of the barrel.

The O-ring is of such cross-sectional area and of such external diameter that when it is in the groove 50 it is wedged therein in such manner as to exert forward pressure on the flange but does not contact the internal wall of the syringe barrel. Thus the O-ring functions only as a spring. It is to be understood that the size of the O-ring is such that it must be stretched in order to place it in the groove 50, and when disposed in said groove it will be wedged therein due to the groove 50 tapering inwardly and being inclined forwardly, the bottom being narrower than the top.

By way of example, the angle of the wall 32 of the body 28 is 45.degree. relative to the axis of the plunger head while the angle of the wall 44 is 75.degree. relative to said axis. Also, the angle of the wall 46 of the flange is 60.degree.. These angles may be varied according to the flange action desired.

There is a part of the plunger head that extends forwardly of the plane of the forward end of the flange. In the arrangement shown in FIG. 2 there is a cylindrical part 56 that extends forwardly from the base of the flange and is about the same diameter as the diameter of the reduced diameter part 30. At the end of the part 56 is an enlarged knob 58. The purpose of this arrangement is to minimize the side of the bore 18 of the barrel ahead of the plunger, thereby providing greater accuracy of control of the discharge of the sample in the syringe.

The plunger member 12 comprises a tubular plunger rod 60 of suitable material such as stainless steel for example. The wall of the plunger rod is relatively thick but has an interior chamber portion 62 at the forward end that is of enlarged diameter so that the wall 64 of the portion 62 is thinner than the wall of the rest of the plunger rod.

The plunger head has an anchoring and support part 66 that extends rearwardly thereof and that is snugly received in the chamber 62. At the junction of the anchoring and support part with the plunger head there is an annular groove 68 in said anchoring and support part, said groove being generally V-shaped in cross section. The forward end of the wall 64 of the plunger rod has an inwardly extending flange 70 having a shape corresponding to the shape of the groove 68 and is disposed therein to secure the plunger head to the plunger rod.

At its outer end the plunger rod has a radially extending annular flange or button 72 secured to the rod by any well-known means. The external diameter of the plunger rod is somewhat smaller than the diameter of the body 28 of the plunger head and said plunger rod, as well as the button 72 is coated with a layer of plastic 74, Teflon being an example of a suitable plastic for the coating 74.

In FIG. 3 there is shown another arrangement of the plunger head. In this arrangement the part that projects forwardly of the flange is a cylindrical part 78, the part 78 being substantially shorter longitudinally than the parts 56 and 58 of the arrangement shown in FIG. 2. Also, there is no groove at the forward end of the anchoring and supporting part 66.

Claims

I claim:

1. A plunger head for a syringe comprising:

A. a cylindrical body;

B. a cylindrical reduced diameter part extending forwardly from the forward end of said body;

C. an annular flange on said reduced diameter part, said flange being spaced forwardly of the forward end of said body, there being an annular outwardly opening groove defined by the adjacent end walls of said body and said flange, said groove being narrower at its base where it joins the reduced diameter part than at the open top part and narrower longitudinally at its base than at the outer free end;

D. a resilient O-ring wedged in the groove exerting forward springlike pressure against and for urging the flange pivotally forwardly and flexing said flange in an annular pivotal base area in the region of the junction of the flange with the reduced diameter part of the plunger head and pressing the outer annular surface of said flange against the interior syringe wall, the outside diameter of said O-ring being no greater than the diameter of the flange;

E. and an anchoring and support part projecting rearwardly of the cylindrical body.

2. The invention defined by claim 1, wherein the outside diameter of the O-ring, when disposed in said groove, is smaller than the diameter of the flange.

3. The invention defined by claim 2, wherein the flange has a plurality of peripheral, cylindrical lands separated longitudinally by peripheral grooves.

4. The invention defined by claim 3, including plunger rod, the anchoring and support part of the plunger head being secured to the front end of said plunger rod.

5. The invention defined by claim 1 wherein the flange has a plurality of peripheral grooves, and peripheral lands at the sides of said grooves.

6. The invention defined by claim 4, including a tubular syringe barrel in which the syringe head and plunger are operably disposed, said flange being in peripheral engagement with the inner wall of the barrel, said barrel having a forward end wall from which a tip extends forwardly, there being a fluid passage through the tip and into the hollow interior of the barrel.

7. The invention defined by claim 4, wherein the plunger rod is hollow and said anchoring and support part of the plunger head is disposed and secured within a forward portion of said plunger rod.

8. The invention defined by claim 1, wherein the forward end of the plunger body has an annular wall adjacent the periphery of the body which is inclined forwardly and inwardly, and the adjacent side of the flange has at least an inner annular wall portion inclined forwardly and inwardly at a greater angle relative to the cylindrical surface of the reduced diameter part than the angle of the adjacent inclined annular wall of the body.

9. The invention defined by claim 8, wherein the forward end of the flange has at least an inner annular wall part that flares from the base of said flange forwardly and outwardly.