Syringe for use in fluid-handling apparatus

Details Syringe for use in fluid-handling apparatus Syringe for use in fluid-handling apparatus

1998-04-17

2001-05-22

Seidel, Richard K. (Department: 3763)

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

C604S122000

Reexamination Certificate

active

06235002

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an improved syringe, and in particular, to an improved displacement-type syringe comprising at least one port at each end of the syringe which are connected in fluid communication via an axially-elongated passageway, the syringe being particularly suitable for use in apparatus for hematological analysis and/or particle counting.
BACKGROUND INFORMATION
Typically, a syringe comprises a hollow syringe cylinder which is open at a first end to accept a plunger, and which includes an axial port at a second end through which fluids may pass. The plunger may be of the forced discharge or of the displacement type, the displacement type having an intentional significant gap between the plunger and the syringe cylinder.
The forced discharge type of syringe relies mainly on a pressure differential between the syringe contents and the discharge port in order to force out the contents. Unfortunately, this type of syringe may display a non-linear relationship between plunger rate and discharge rate due in part to internal fluid dynamics, especially near the extremes of plunger travel. The displacement type of syringe generally displays a more linear relationship between plunger rate and discharge rate.
A common goal with many types of syringes is to eliminate gas within the hollow syringe cylinder. Displacement-type syringes may be generally more susceptible to gas build-up than other types mainly because of the substantial non-displaced volume remaining within a displacement-type syringe even at full plunger travel.
Syringes mounted in fluid-handling apparatus, such as apparatus for hematological analysis and/or particle counting, may be especially plagued by gas build-up due to the inability to conveniently reorient and reposition the syringe in order to expel a gas bubble. A significant problem with gas bubbles is that they act as pressure and vacuum reservoirs which especially reduce the displacement accuracy of the syringe. In addition, expelling the gas from a syringe mounted downwards may be nearly impossible with many prior art fluid-handling apparatus.
Accordingly, it is an object of the present invention to facilitate an improved displacement-type syringe suitable for mounting in fixed, fluid-handling apparatus and which overcomes the above-described drawbacks and disadvantages of the prior art.
SUMMARY OF THE INVENTION
The present invention is directed to a syringe comprising a syringe housing, a plunger slidably received within the syringe housing, and a longitudinally-extending passageway formed between the plunger and syringe housing. A fixed seal is mounted at approximately one end of the longitudinally-extending passageway, and the plunger is slidably received and movable through the seal to displace fluid into and out of the syringe housing. At least one fluid port is located at approximately one end of the longitudinally-extending passageway, and at least one other fluid port is located at approximately the other end of the passageway in fluid communication with the other fluid port to permit the flow of fluid and gas into and out of the passageway regardless of the orientation of the syringe. Thus, the plunger displaces a known volume of fluid corresponding to its volumetric displacement, but otherwise leaves fluid within the syringe passageway. Any gas or bubbles left within the passageway are permitted to flow out through one or both fluid ports at either end of the passageway to thereby maintain the syringe in a gas-free state.
One advantage of the invention is that the syringe may be mounted at any angle of inclination including horizontally (although a substantially horizontal orientation, having an inclination of approximately two to five degrees, is preferred), and still be substantially impervious to gas accumulation. Thus the syringe will remain accurate over a wider range of fixed mounting positions than permitted under the prior art.
Another advantage is that the seal which is fixedly mounted at one end of the longitudinally-extending passageway has the smooth plunger as its only sliding surface, thus reducing friction, wear, and distortion in comparison to prior art syringes that may slide a seal against the inside surface of a syringe housing. Thus the seal is subjected to lower friction than a moving seal in a typical prior art syringe, resulting in lower wear, longer life, less seal distortion, and/or higher accuracy.
Other advantages of the present invention will become apparent in view of the following detailed description and accompanying drawings.


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