US2893391A - Injection apparatus - Google Patents

Description

July 7, J G v As c 2,893,391

INJECTION APPARATUS Filed Aug. 19, 1958 INVENTOR.

ATTORNEYS 2,893,391 Patented July 7, 1959 INJECTION APPARATUS John G. Vlasic, Harvey, Ill., assignor, by mesne assignments, to Sinclair Research Laboratories, Inc, Harvey,

111., a corporation of Delaware Application August 19, 1958, Serial No. 755,950

1 Claim. (Cl. 128-218) This invention relates to syringes which dispense measured quantities of fluid and more particularly to an improved syringe of simple and durable construction capable of dispensing fluid in very small approximately identical amounts.

An object of this invention is to provide an apparatus operable by unskilled individuals, capable of dispensing exact, minute, almost identical amounts of fluid an indefinite number of times without measurement.

Another object is to provide a syringe constructed of commonly available materials but, nevertheless, exceptionally rugged and particularly adapted for use with exceedingly small quantities of material. Ordinary tubing or pipe may be used for the plunger and standard syringe barrel for the body.

A further object of this invention is to provide a novel plunger and barrel relationship in which plunger-barrel leakage is inconsequential, which insures exclusion of air from the apparatus and prevents internal plunger-barrel Wear.

A conventional syringe apparatus, hereafter referred to as piston type, operates in two strokes. The intake or supply stroke fills the syringe in this manner: the piston is depressed as far as possible, the syringe needle is placed in the supply fluid and the piston withdrawn to draw the desired amount of fluid into the syringe body or barrel. While this system is satisfactory for ordinary use, several inherent factors combine to produce excessive error when very small quantities of fluid are involved. During the supply stroke, complete elimination of air is virtually impossible and while the amount of air involved may be small, its presence causes several undesirable eifects.

Since air is easily compressible, some of the force applied by the piston during the ejection stroke compresses the trapped air. Thus, initially the piston applies force to compress the air rather than eject the fluid and therefore, the piston moves a greater distance at first to eject a given quantity than later. Usually, the quantity of fluid ejected is determined by multiplying the distance the piston has moved by the known cross-sectional area of the piston. However, when air is contained in the apparatus the compression of the air varies in proportion to the speed of plunger movement, the amount of air trapped, the resistance encountered at discharge, etc. These factors are diflicult to determine and ordinarily result in small errors which can be ignored. However, when quantitative accuracy of very small amounts of fluid is required this eifect can cause large relative errors in the volume of fluid ejected. Minimum error may be effected by careful grinding of the mating parts but wear between the piston and barrel walls will result in relatively large discrepancies within a short period. In the apparatus of my invention air is expelled in a single filling operation and no skill or care is required to assure complete certainty.

The invention can more readily be understood in view of the drawings.

In the accompanying drawings:

Figure 1 is an exploded perspective view of a syringe according to the invention, showing the parts in assembly position;

Figure 2 is the side elevation of the syringe; and

Figure 3 is a cross-sectional view of the valve assembly attached to the plunger.

The syringe is composed of a barrel 1, adapted at one end to fit into and secure needle 2, and open at theopposite end to accommodate tapered portion 3 of annular collar 4. Collar 4 contains a longitudinal passage 5, in which hollow plunger 6 travels, in sealing engagement with collar 4. Valve housing 7 is permanently attached to the remote end of plunger 6. Housing 7 contains longitudinal bore "10 communicating with the bore of plunger 6 in one direction, and terminating in valve seat 11 in the other direction. Needle valve 9 engages housing 7 obstructing flow through hollow plunger 6 to vent 8 when in the closed position, and permitting flow when separated from the valve seat 11.

In the operation of my syringe, the plunger is placed in the extended position, i.e. the lower end of the plunger even with the bottom of the collar, and the valve is opened. Fluid is supplied underpressure until it flows from the vent, at which time the valve is closed and the supply removed. At this point the apparatus is entirely filled with fluid and all air has been eliminated. Compressibility of air is no longer a factor and movement of the plunger accurately indicates the quantity dispensed.

Since the filling stroke does not require drawing the fluid into the syringe by creating a vacuum in front of the piston, sealing action between the plunger and barrel is not necessary. Further, fluid is ejected by displacement of the plunger as it moves into the barrel and not by the action of a piston forcing the fluid out of the barrel. Leakage around the piston of a conventional syringe occurs not only on filling, i.e. air leaking in, but on the ejection stroke as well, i.e. fluid leaking out around the piston, thus compounding the measuring error. It can be seen that for reasonably quantitative results with conventional equipment an accurately ground, sealing piston is necessary. In my invention, the novel design, allows this simple filling operation, thus an ordinary tubing or pipe can be used as a plunger and contact with the sides of the syringe barrel is neither necessary nor desirable. For most uses, an external tubing diameter at least 2 millimeters smaller than the internal diameter of the barrel has been found preferable. This allows ade quate sealing area for the tapered portion of the annular collar between the syringe barrel and the tubing or plunger. The plunger can be conventional tubing, preferably stainless steel and machining or grinding is not required. Since mating the plunger with the barrel is unnecessary, the partially tapered annular collar, preferably made of rubber, polytetrafluoroethylene, or other low pressure polyethylene, can fit any standard size syringe barrel.

In conventional equipment, frequently a reading must be taken at the beginning and a second reading at the end of a stroke to determine the amount of discharge. However, in my syringe since the starting and ending points of the discharge stroke are always the same; respectively, when the plunger is just even with the lowest part of the tapered portion of the collar, and when the valve housing is bottomed against the annular collar, the quantity of fluid discharged is positively determined. The accompanying error is obviously less than the conventional two-reading method.

In the previous paragraphs, the invention has been described for general utility. However, an important use is in vapor phase chromatography. In chromatography,

it is necessary to apply very small virtually identical samples. This invention is ideal in elfecting the delivery of identical, minute quantities of flud. That is, each time it is properly loaded it will eject. exactly the same amount of fluid without any measurement required. This is accomplished by a simple mechanical operation. The plunger is placed through the longitudinal passage in the collar and gently tapped back until it is just even with the bottom of the tapered portion ofthe collar, then the collar is secured to the barrel; the apparatus is then supplied with fluid under pressure as previously described. When discharge is desired the plunger is forced all the way down until the bottom of the valve housing contacts the upper portion of the collar. Inthis way exactly the same amount of fluid may be dischargedeachtime. The length or diameter of the tubing can be varied until a plunger of the desired displacement value is obtained. Thereafter the same plunger and collar with any standard syringe barrel will dispense the same quantity of fluid each time it is used.

From the foregoing, it can be: seen that my invention provides a novel syringe in which it is not necessary to have the plunger and barrel mate. The perpetual problem of leakage around the piston member of conventional syringe apparatus is obviated. The new syringe is airbubble-free and can use interchangeable syringe bodies of standard sizes. Standard syringe barrels are much less expensive than precisely ground, narrow gauge barrels generally used. It is capable of discharging very small precise amounts of fluid even when used with relatively large diameter syringe barrels. The quantity discharged can be identically reproduced in an indefinite number of applications without measurement. Since the plunger and barrel do not mate, wear and resulting error are prevented. Also, since mating is unnecessary, ordinary inexpensive tubing can be used for the plunger. Air leakage into, and fluid leakage out of the apparatus is avoided, permitting more accurate readings and greater reliability when operated by semior unskilled personnel.

In situations requiring minute quantities, the plunger diameter can be quite small without varying the size of the syringe body and the length of the stroke can be longer to eject a given quantity of sample. The relative measurement error for the same amount of sample decreases with longer strokes. To accomplish the same effect a piston type syringe would have to be very narrow requiring extensive grinding or machining in order to achieve adequate mating of the tiny parts; 'I hese narrow gauge syringes are difficult to hold and are delicate. Furthermore, readings must be made with great care and skill to discharge precisely the correct amount of fluid. With my device a largeba'rrel may be used resulting in greater ease of handling and strength of construction. With the proper size plunger the exact quantity can be applied Without involvingany measurements.

It is understood that the drawings and description are illustrative only, and various modifications and changes may be made without departing from the spirit of the invention.

I claim:

A syringe comprising a barrel, a plunger having a longitudinal bore, an annular collar rigidly sealing an end of said barrel and having a passage adapted to admit said plunger in sealing engagement, the plunger having a diameter substantially smaller than the internal diameter of the barrel, a valve affixed to the end of said plunger external of said barrel and having a vent communicating with the bore of said plunger when the valve is open.

References Cited in the file of this patent UNITED STATES PATENTS

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