Non-reusable hypodermic syringe

• US 5,254,093 A
• Filed: 02/12/1990
• Issued: 10/19/1993
• Est. Priority Date: 02/12/1990
• Status: Expired due to Fees

• Current Assignee: Medical Appliances Incorporated
• Original Assignee: Medical Appliances Incorporated
• Inventors: Linn, Gail F., Bartlett, Joseph W.
• Primary Examiner(s): Rosenbaum, C. Fred
• Assistant Examiner(s): Bockelman, Mark
• Application Number:
  US07/478,667
• Time in Patent Office: 1,345 Days
• Field of Search: 604/110, 604/111, 604/187, 604/199, 604/218, 604/221, 604/236-238, 604/240, 604/245, 604/220
• US Class Current: 604/110
• CPC Class Codes: A61M 2005/3128 Incorporating one-way valves, e.g. pressure-relief or non-return valves
• CPC Class Codes: A61M 2005/3132 having flow passages for injection agents at the distal end of the barrel to bypass a sealing stopper after its displacement to this end due to internal pressure increase
• CPC Class Codes: A61M 2005/5053 Valve or plug actuated by fluid flow or fluid pressure allowing initial filling of the syringe
• CPC Class Codes: A61M 5/5013 Means for blocking the piston or the fluid passageway to prevent illegal refilling of a syringe

Abstract

A single use disposable hypodermic syringe having a hollow elongated barrel portion, a piston and sealing engagement with an axially translatable along the barrel portion, a piston rod secured to the piston and projecting from the rearward end of the barrel portion for use in reciprocating the piston, a walled chamber disposed proximate the forward end of the barrel portion and plug means disposed in the chamber and moveable therein from a rearward position to a forward position in response to liquid being forced against the plug member by the piston. The plug member defines fluid passages therein to allow fluid flow about the plug member and an annular flange which cooperates with the interior surface of the chamber for maintaining the plug member in the rearward position upon air being passed through the fluid passages in response to translation of the piston within the barrel portion. The annular flange also cooperates with a second portion of the chamber wall for permanently maintaining the plug member in the forward position upon the plug member being moved to the forward position by the liquid during ejection thereon from the syringe. With the plug member in the forward position, the annular flange thereon seals the fluid passages upon the piston being retracted within the barrel portion toward the rearward end thereof to prevent any additional liquid from being aspirated into the barrel portion of the syringe about the plug member thereby rendering the syringe non-reusable.

Claims

1. A single use disposable hypodermic syringe comprising:

a hollow elongated barrel portion;

a piston in sealing engagement with and axially translated along said barrel portion;

a piston rod secured to said piston and projecting from one end of said barrel portion for use in reciprocating said piston;

a walled chamber disposed proximate the other end of said barrel portion;

a first plug member disposed in said chamber and moveable therein from a rearward position to a forward position;

a second plug member disposed forwardly of said first plug member;

fluid flow means disposed in said first plug member for allowing fluid flow therethrough;

means defined by said first plug member for maintaining said first plug member in said rearward position upon air being drawn into and ejected from said barrel portion through said fluid flow means in response to translation of said piston within said barrel portion and for permanently maintaining said first plug member in said forward position upon said first plug member being moved to said forward position by said liquid during ejection thereof from said syringe; and

means defined by said second plug member for sealing said fluid flow means upon said first plug member being forced to said forward position and said piston being retracted within said barrel portion toward said one end thereof to prevent any additional liquid from being drawn into said barrel portion through said fluid flow means thereby rendering said syringe non-reusable.

2. A single use disposable hypodermic syringe comprising:

a hollow elongated constant diameter barrel portion;

a piston in sealing engagement with and axially translatable along said barrel portion;

a piston rod secured to said piston and projecting from one end of said barrel portion for use in reciprocating said piston;

a walled chamber disposed proximate the other end of said barrel portion;

a first plug member disposed in said chamber and defining means therein to allow fluid flow therethrough, said plug member being moveable from a rearward position to a forward position in response to liquid being forced against said plug member by said piston;

a second plug member disposed in said chamber forwardly of said first plug member and defining means for allowing liquid flow about said second plug member for ejection from said syringe and means for sealing said fluid flow means in said first plug member upon said second plug member being forced against said first plug member when said first member is in said forward position; and

means for maintaining said first plug member in said rearward position upon air being passed therethrough in response to translation of said piston within said barrel portion and for permanently maintaining said plug member in said forward position upon said first plug member being moved to said forward position by said liquid during ejection thereof from said syringe such that upon said first plug member being forced to said forward position and said piston being retracted within said barrel portion toward said one end thereof, said second plug member is caused to be drawn rearwardly within said chamber against said first plug member, sealing said fluid flow means therein and preventing any additional liquid from being aspirated into said barrel through said first plug member thereby rendering said syringe non-reusable.

3. The syringe of claim 2 wherein said maintaining means comprises an annular resilient flange projecting from said first plug member against a portion of the wall of said chamber and a radial shoulder defined by said wall such that upon said first plug member being forced from said rearward position to said forward position, said flange passes forwardly of said shoulder and flexes radially outwardly therefrom, and upon said piston being subsequently retracted within said barrel portion, abuts said shoulder to maintain said first plug member in said forward position.

4. The syringe of claim 3 wherein said fluid flow means in said first plug member comprises a fluid flow channel extending axially therein and communicating with a conical recess formed in said first plug member and wherein said sealing means on said second plug member comprises a conical extension thereon adapted to be received within said recess in said first plug member and seal said fluid flow channel therein.

5. The syringe of claims 2, 3 or 4 including a cap member disposed about the forward end of said walled chamber, said cap member defining a central opening in the forward end thereof and wherein said second plug member is axially moveable within said chamber between the forward end of said cap member and the forward end of said chamber wall.

6. The syringe of claim 5 wherein said piston rod defines an enlarged portion at the forward end thereof, said portion being received and held within a correspondingly configured recess in said piston such that upon said first plug member being disposed in the forward position and said piston being retracted within said barrel portion, a vacuum is created between said piston and said first plug member causing said enlarged portion of said piston rod to be pulled from said recess, rendering said piston rod incapable of further reciprocation of said piston.

7. A single use disposable hypodermic syringe comprising:

a hollow elongated barrel having a forward end and a rearward end;

a piston in sealing engagement with and axially translatable along a first portion of said barrel;

a piston rod secured to said piston and projecting from the rearward end of said barrel for use in reciprocating said piston;

a first plug member disposed in a second portion of said barrel forwardly of said piston, said member being moveable from a rearward position to a forward position within said second barrel portion in response to liquid being forced against said member by said piston and defining a fluid flow channel extending axially therethrough;

a second plug member disposed in said barrel forwardly of said first plug member and defining one or more channels therein for the passage of fluid about said second plug member and means thereon for sealing said fluid flow channel in said first plug member upon said plug members being disposed in an abutting relationship to prevent fluid flow through said channel; and

means for maintaining said first plug member in said rearward position and spaced from said second plug member to allow a variable volume of air to be drawn into and ejected from said barrel through said channel in said first plug member and about said second plug member in response to reciprocation of said piston within said barrel prior to liquid being drawn into said barrel whereby said syringe can operate as an air pump and, upon liquid being drawn into said barrel about said second plug member and through said channel in said first plug member and said first plug member being forced forwardly within said barrel to said forward position during ejection of liquid from said barrel by the force of the liquid acting on said first plug member, said means maintains said first plug member in said forward position such that upon said piston being retracted toward said rearward end of said barrel, said second plug member is caused to be drawn rearwardly against said first plug member, sealing said fluid flow channel in said first plug member and preventing any additional fluid from being drawn into said barrel through said first plug member thereby rendering said syringe non-reusable.

8. The syringe of claim 7 wherein said maintaining means comprises an annular resilient flange formed with and projecting outwardly from said first plug member and bearing against a first portion of said barrel when said first plug member is disposed in said rearward position to maintain said plug member in said rearward position prior to the ejection of liquid from said barrel, and a stop member in said barrel disposed forwardly of and radially outwardly from said first portion of said barrel such that upon said first plug member being forced to said forward position by said liquid during ejection thereof, said flange passes forwardly of said stop member, flexes outwardly and bears against a second portion of said barrel disposed below said stop member whereby said first plug member is permanently held in said forward position by the abutment of said flange with said stop member.

9. The syringe of claims 7 or 8 wherein said first plug member includes a conical chamber formed therein communicating with said fluid flow channel and wherein said sealing means defined by said second plug member comprises a conical extension thereon adapted to be received within said chamber in said first plug member and seal said fluid flow channel therein.

10. The syringe of claim 9 including a cap member disposed about the forward end of said barrel and defining a central opening in the forward end thereof, said second plug member being axially moveable between the forward end of said cap member and the forward end of said barrel.

11. The syringe of claims 7 or 8 wherein said piston rod defines an enlarged portion at the forward end thereof, said portion being received and held within a correspondingly configured recess in said piston such that upon said first plug member being disposed in said forward position and said piston being retracted in said barrel, a vacuum is created between said piston and said first plug member such that upon retracting said piston within said barrel, said enlarged portion of said piston rod is caused to be pulled from said recess, rendering said piston rod incapable of further reciprocation of said piston.

12. A single use hypodermic syringe comprising:

a hollow elongated barrel having a forward end, a rearward end, and a constant diameter portion adjacent said rearward end;

a piston in sealing engagement with and axially translatable along said constant diameter portion of said barrel;

a piston rod secured to said piston and projecting from said rearward end of said barrel for use in reciprocating said piston;

a first plug member disposed in said barrel forwardly of said piston and defining a fluid flow channel extending axially therethrough and means cooperating with said barrel for retaining said plug member within a first portion of said barrel as a variable volume of air is drawn into and ejected from said barrel in response to translation of said piston within said barrel prior to liquid being drawn into said barrel whereby said syringe can operate as an air pump, said means, retaining said plug member within a second portion of said barrel upon liquid having been drawn into said barrel and ejected therefrom through said channel so as to move the plug from first to second portion of the barrel; and

a second plug member spaced from said first plug member, said second plug member having flow passages therein for the passage of fluid about said second plug member and means thereon for sealing said channel in said first plug member upon said first plug member being disposed within said second portion of said barrel and said piston being retracted toward said rearward end thereof whereby liquid is prevented from being further drawn into said barrel through said first plug member, rendering said syringe non-reusable.

13. The syringe of claim 12 wherein said piston rod defines an enlarged portion at the forward end thereof, said portion being received and held within a correspondingly configured recess in said piston such that upon said first plug member being disposed in said second portion of said barrel and said piston being retracted within said barrel, a vacuum is created between said piston and said first plug member such that upon retracting said piston within said barrel, said enlarged portion of said piston rod is caused to be pulled from said recess, rendering said piston rod incapable of further reciprocation of said piston.

14. The syringe of claims 12 or 13 wherein said barrel defines a first stop member and a second stop member, said second stop member being disposed forwardly of and spaced radially outwardly from said first stop member and wherein said cooperating means comprises an annular resilient flange formed with and projecting outwardly from said first plug member and bearing against a portion of said barrel below said first stop member when said first plug member is disposed in said first portion of said barrel thereby restricting the rearward movement of said first plug member in said barrel and maintaining said first plug member in place as air is drawn into and ejected from said barrel and, upon said first plug member being forced to said second portion by said liquid during ejection thereof, said flange passes forwardly of said second stop member, flexes outwardly and bears against a portion of the barrel disposed below said second stop member whereby said first plug member is permanently held within said second portion of said barrel by the abutment of said flange with said second stop member.

15. A single use disposable hypodermic syringe comprising:

a hollow elongated barrel having a forward end, a rearward end and a constant diameter portion adjacent said rearward end;

a piston in sealing engagement with and axially translatable along said constant diameter portion of said barrel;

a piston rod secured to said piston and projecting from said rearward end of said barrel for use in reciprocating said piston;

a cap member secured to and disposed about said forward end of said barrel and defining a central opening therein;

a cannula means carried by said cap member and communicating with said central opening;

a first plug member disposed in said barrel forwardly of said piston and defining a fluid flow channel extending axially therethrough, a first stop means adapted to abut a first shoulder defined by said barrel to limit the forward movement of said plug member within said barrel, and an annular resilient flange member in sealing engagement with said barrel to prevent fluid flow therebetween and retain said plug member within a first portion of said barrel as a variable volume of air is drawn into and out of said barrel through said cannula means prior to liquid being drawn into said barrel whereby said syringe can operate as an air pump and, upon said plug member being forced forwardly of said first portion of said barrel during the ejection of liquid from said barrel by the force of the liquid acting on said plug member, to cooperate with a second shoulder defined by said barrel to retain said plug member within a second forward portion of said barrel; and

a second plug member disposed forwardly of said first plug member and defining means thereon for sealing said fluid channel in said first plug member upon said first plug member being disposed in said second forward portion of said barrel and said piston being retracted toward said rearward end of said barrel, whereby any additional liquid is prevented from being drawn into said barrel through said flow channel in said first plug member thereby rendering said syringe non-reusable.

16. The syringe of claim 15 wherein said piston rod defines an enlarged portion at the forward end thereof, said portion being received and held within a correspondingly configured recess in said piston such that upon said first plug member being disposed in said second portion of said barrel and said piston being retracted within said barrel, a vacuum is created between said piston and said first plug member such that upon retracting said piston within aid barrel, said enlarged portion of said piston rod is caused to be pulled from said recess, rendering said piston rod incapable of further reciprocation of said piston.

17. The syringe of claims 15 or 16 wherein said first plug member defines a conical chamber therein communicating with said fluid channel and wherein said sealing means defined by said second plug member comprises a conical extension thereon adapted to be received within said chamber in said first plug member and seal said flow channel therein.

18. A single use disposable hypodermic syringe comprising:

a hollow elongated barrel portion;

a piston in sealing engagement with and axially translatable along said barrel portion;

a piston rod secured to said piston and projecting from one end of said barrel portion for use in reciprocating said piston;

a walled chamber disposed proximate the other end of said barrel portion; and

axially translatable plug means constructed of a liquid impervious material disposed in said chamber and movable therein from a rearward position to a forward position, said plug means defining fluid flow means therein, said fluid flow means being continuously open when said plug means is in said rearward position and, prior to liquid being drawn into said barrel portion, a allowing a variable volume of air to pass therethrough and be drawn into and ejected from said barrel portion in response to translation of said piston within said barrel portion during the use of the syringe as an air pump and, upon liquid being drawn into said barrel portion through said fluid flow means and least a portion thereof ejected from said syringe, said plug means sealing said fluid flow means in response to said piston being retracted within said barrel portion toward said one end thereof and preventing any additional liquid from being aspirated into said barrel portion through said fluid flow means thereby rendering said syringe non-reusable.

19. The syringe of claim 18 wherein said piston rod defines an enlarged portion at the forward end thereof, said portion being received and held within a correspondingly configured recess in said piston such that upon said plug member being disposed in said forward position and said piston being retracted in said barrel, a vacuum is created between said piston and said first plug member such that upon retracting said piston within said barrel, said enlarged portion of said piston rod is caused to be pulled from said recess, rendering said piston rod incapable of further reciprocation of said piston.

20. A single use disposable hypodermic syringe comprising:

a hollow elongated barrel;

a piston in sealing engagement with and axially translatable along said barrel portion;

a piston rod secured to said piston and projecting from one end of said barrel portion for use in reciprocating said piston;

a first plug member disposed in a portion of said barrel forwardly of said piston and moveable from a rearward position to a forward position in response to liquid being forced against said plug member by said piston, said plug member defining a fluid flow channel therein for allowing a variable volume of air to pass therethrough and be drawn into and ejected from said barrel in response to translation of said piston within said barrel prior to liquid being drawn into said barrel whereby said syringe can operate as an air pump;

means for permanently maintaining said first plug member in said forward position upon said plug member being moved to said forward position; and

a second plug member movably disposed in said barrel forwardly of said first plug member, said second plug member defining closure means thereon for sealing said fluid flow channel upon said first plug member being disposed in said forward position and said closure means being drawn into sealing engagement with said channel upon the retraction of said piston within said barrel.

21. A single use disposable hypodermic syringe comprising:

a hollow elongated barrel portion;

a piston in sealing engagement with and axially translatable along said barrel portion;

a piston rod secured to said piston and projecting from one end of said barrel portion for use in reciprocating said piston;

a walled chamber disposed proximate the other end of said barrel portion;

a plug member disposed in said chamber and movable therein from a rearward position to a forward position in response to liquid being forced against said plug member by said piston, said plug member having a fluid flow channel therein allowing for the passage of fluid therethrough to and from said barrel portion when said plug member is in said rearward position;

resilient retaining means carried by said plug member for retaining plug member in said rearward position prior to liquid being drawn into said barrel portion and allowing a variable volume of air to be drawing into and ejected from said barrel portion through said channel when said piston is reciprocated within said barrel portion during the use of said syringe as an air pump; and

means disposed in said chamber for closing said fluid flow channel in response to said piston being retracted within said barrel portion toward said one end thereof upon liquid having been drawn into said barrel portion and said plug member moved to said forward position by the ejection of at least a portion of said liquid from said barrel portion thereby preventing any additional liquid from being drawn into said barrel portion and rendering said syringe non-reusable.

22. The syringe of claim 21 wherein said plug member comprises a body portion, a cylindrical portion disposed rearwardly of said body portion and defining a rear plug surface at the rearward end thereof, and an annular resilient flange disposed forwardly of said body portion, said flange defining a forward plug surface at the forward end thereof, said retaining means comprising said annular resilient flange, and said fluid flow channel comprising a first fluid passageway disposed in said rearward plug surface and a second fluid passageway disposed in said forward plug surface, said second fluid passageway communicating with said first fluid passageway when said plug member is in said rearward position.

23. The syringe of claim 21 wherein said retaining means comprises a resilient annular flange defined by said plug member, said walled chamber defines a first annular wall portion extending about a rearward portion of said chamber and a second wall portion extending about a forward portion of said chamber and defining an enlarged diameter portion of said chamber, and said closing means comprises an annular shoulder disposed in said chamber between said first and second wall portions, said resilient flange being disposed in a flexed disposition and bearing against said first wall portion of said chamber when said plug member is in said rearward position, extending radially outwardly from said plug member in an unflexed disposition within said enlarged diameter portion of said chamber when said plug member is in said forward position and, upon said piston being retracted within said barrel portion toward said one end thereof when said plug member is in said forward position said flange bears against said shoulder, closing said fluid flow channel.

24. The syringe of claim 21 wherein said walled chamber defines a first annular wall portion extending about a rearward portion of said chamber and a second annular wall portion extending about a forward portion of said chamber and defining an enlarged diameter portion of said chamber, said retaining means comprising an annular resilient flange, said flange defining a forward plug surface at the forward end thereof and annular side wall adjacent thereto, said fluid flow channel extending through said forward plug surface and a forward portion of said adjacent side wall, said flange being disposed in a flexed disposition when said plug member is in a said rearward position with said plug surface bearing against said first wall portion and, upon said plug member being moved to said second position, said flange extends radially outwardly from said plug member within said enlarged diameter portion of said chamber, and wherein said closing means comprises an annular shoulder disposed within said chamber between said first and second wall portions thereof, said shoulder cooperating with said flange to close said fluid flow channel when said plug member is in said forward position and upon said flange being drawn against said shoulder in response to said retraction of said piston.

25. The syringes of claims 23 or 24 including an annular stop member disposed in said barrel portion between said piston and said plug member, said stop member including an inwardly projecting radial portion for limiting the rearward movement of said plug member in said chamber, an aperture in said radial portion for the passage of fluid therethrough and an annular depending portion defining said first wall portion in said chamber and said shoulder.

26. The syringe of claim 21 wherein said retaining means is integrally formed with said plug member and said fluid flow channel comprises a plurality of fluid flow passageways, said passageways being formed in and spaced equidistantly apart about said resilient retaining means.

27. A single use disposable hypodermic syringe comprising:

a hollow elongated barrel portion;

a piston in sealing engagement with and axially translatable along said barrel portion;

a piston rod secured to said piston and projecting from one end of said barrel portion for use in reciprocating said piston;

a walled chamber disposed proximate the other end of said barrel portion, said chamber having a first annular side wall portion extending about a rearward portion thereof, a second annular side wall portion extending about a forward portion thereof and defining an enlarged diameter portion of said chamber, and an annular shoulder disposed in said chamber between said first and second wall portions;

a plug member disposed in said chamber and movable therein from a rearward position to a forward position in response to liquid being forced against said plug member by said piston, said plug member defining a body portion, a cylindrical portion disposed rearwardly of said body portion, and a rear plug surface at the rearward end thereof;

a resilient flange defined by said plug member and disposed thereon forwardly of said body portion, said flange defining a forward plug surface at the forward end thereof, an annular side wall adjacent said forward plug surface, and a diameter greater than the inner diameter of said first wall portion of said chamber and less than the diameter of said second wall portion, said flange being in a flexed disposition and bearing against said first wall portion of said chamber when said plug member is in said rearward position;

a firs fluid flow channel disposed in said flange and extending through said forward plug surface and a forward portion of said annular side wall, said fluid flow channel communicating with said barrel portion, thereby allowing for the passage of fluid therethrough to and from said barrel portion, said flange maintaining said plug member in said rearward position prior to liquid being drawn into said barrel portion and allowing a variable volume of air to be drawn into and ejected from said barrel portion through said fluid flow-channel when said piston is reciprocated within said barrel portion during the use of said syringe as an air pump; and

upon said plug member being moved to said forward position by liquid being forced against such said plug member by said piston, said flange flexes outwardly within said enlarged diameter portion of said chamber such that upon said piston being subsequently retracted within said barrel portion toward said one end thereof, said flange is drawn against said shoulder in said chamber, sealing said fluid flow channel and preventing any additional liquid from being drawn into said barrel portion, thereby rendering said syringe non-reusable.

28. The syringe of claim 27 wherein said cylindrical portion of said plug member defines an annular side wall adjacent said rear plug surface and a second fluid flow channel extending through said rearward plug surface and a forward portion of said adjacent side wall, said second fluid flow channel communicating said first fluid flow channel when said plug member is disposed in said rearward position.

29. A single use disposable hypodermic syringe comprising:

a hollow elongated barrel portion;

a piston in sealing engagement with and axially translatable along said barrel portion;

a piston rod secured to said piston and projecting from one end of said barrel portion for use in reciprocating said piston;

a walled chamber disposed proximate the other end of said barrel portion and defining an annular shoulder therein;

a plug member disposed in said chamber and movable therein from a rearward position to a forward position in response to liquid being forced against said plug member by said piston, said plug member having a fluid flow channel therein for the passage of fluid therethrough to and from said barrel portion when said plug member is in said rearward position and defining a resilient retaining means for retaining said plug member in said rearward position prior to liquid being drawn into said barrel portion and allowing a variable volume of air to be drawn into and ejected from said barrel portion through said channel when said piston is reciprocated within said barrel portion during the use of said syringe as an air pump and, upon liquid being drawn into said barrel portion through fluid flow channel and at least a portion thereof ejected from said barrel portion, said plug member cooperates with said shoulder to seal said channel in response to said piston being retracted within said barrel portion toward said one end thereof, thereby preventing any additional liquid from being drawn into said barrel portion through said channel and rendering said syringe non-reusable.

30. The syringe of claim 29 wherein said fluid flow channel comprises a plurality of fluid flow passageways, said passageways being formed in and spaced equidistantly apart about said resilient retaining means.

31. A single use disposable hypodermic syringe comprising:

a hollow elongated barrel portion;

a piston in sealing engagement with and axially translatable along said barrel portion;

a piston rod secured to said piston and projecting from one end of said barrel portion for use in reciprocating said piston;

a walled chamber disposed proximate the other end of said barrel portion;

a first plug member disposed in said chamber and movable therein from a rearward position to a forward position in response to liquid being forced against said plug member by said piston;

a fluid flow channel extending axially through said first plug member for allowing a variable volume of air to pass therethrough and be drawn into and ejected from said barrel portion when said first plug member is in said rearward position;

means for retaining said first plug member in said rearward position when said piston is reciprocated within said barrel portion prior to liquid being drawn into said barrel portion during the use of the syringe as an air pump;

means for permanently maintaining said first plug member in said forward position upon said plug member being moved to said forward position by liquid being forced against said first plug member by said piston during the ejection thereof from said barrel portion; and

a second plug member disposed in said barrel portion forwardly of said first plug member, said second plug member being axially movable within said barrel portion and defining closure means thereon for sealing said fluid flow channel upon said first plug member being disposed in said forward position and said closure means being drawn into sealing engagement with said first plug member by the retraction of said piston within said barrel portion toward said one end thereof.

32. A single use disposable hypodermic syringe comprising:

an elongated barrel portion;

a piston in sealing engagement with and axially translatable along said barrel portion;

a piston rod secured to said piston and projecting from one end of said barrel portion for use in reciprocating said piston;

a walled chamber disposed proximate the other end of said barrel portion, said chamber having a first annular wall portion extending about a rearward portion thereof, a second wall portion extending about a forward portion thereof and defining an enlarged diameter portion of said chamber, and an annular shoulder disposed in said chamber between said first and second wall portions;

a fluid flow channel disposed in said first wall portion and said shoulder communicating said forward portion of said chamber with said rearward portion thereof;

a plug member disposed in said chamber and movable therein from a rearward position to a forward position in response to liquid being forced against said plug member by said piston; and

an annular resilient flange carried by said plug member and bearing against said first wall portion of said chamber when said plug member is in said rearward position, retaining said plug member in said rearward position prior to liquid being drawn into said barrel portion and allowing a variable volume of air to be drawn into and ejected from said barrel portion through said fluid flow channel when said piston is reciprocated within said barrel portion during the use of said syringe as an air pump, said flange extending radially outwardly from said plug member within said enlarged diameter portion of said chamber when said plug member is in said forward position and, upon said piston being retracted within said barrel portion toward said one end thereof when said plug member is in said forward position, said flange bears against said shoulder, closing said fluid flow channel and preventing any additional liquid from being drawn into said syringe barrel portion.

33. The syringe of claim 32 wherein said piston rod defines an enlarged portion at the forward end thereof, said portion being received and held within a correspondingly configured recess in said piston such that upon said plug member being disposed in said forward position of said barrel portion and said piston being retracted within said barrel, a vacuum is created between said piston and said plug member causing said enlarged portion of said piston rod to be pulled from said recess, rendering said piston rod incapable of further reciprocating of said piston.

34. The syringe of claim 32 wherein said fluid flow channel comprises a plurality of fluid flow passageways, said passageways extending through and being spaced equidistantly apart about said shoulder and said first wall portion.

35. A single use disposable hypodermic syringe comprising:

an elongated barrel portion;

a piston in sealing engagement with and axially translatable along said barrel portion;

a piston rod secured to said piston and projecting from one end of said barrel portion for use in reciprocating said piston;

a walled chamber disposed proximate the other end of said barrel portion and defining an annular shoulder therein;

a plug member having a rearward end and a forward end and disposed in said chamber proximate said annular shoulder and movable therein from a rearward position to a forward position in response to liquid being forced against said plug member by said piston;

a fluid flow channel disposed in said shoulder and extending rearwardly of said rearward end of said plug member when said plug member is in said rearward position for the passage of fluid therethrough to and from said barrel portion;

a resilient retaining means carried by said plug member for retaining said plug member in said rearward position prior to liquid being drawn into said barrel portion and allowing a variable volume of air to be drawn into and ejected from said barrel portion through said fluid flow channel when said piston is reciprocated within said barrel during the use of the syringe as an air pump and, upon liquid being drawn into said barrel portion through said fluid flow channel and at least a portion thereof ejected from said barrel portion, said resilient retaining means flexes outwardly to cooperate with said annular shoulder to seal said fluid flow channel in response to said piston being retracted within said barrel portion toward said one end thereof, thereby preventing any additional liquid from being drawn into said barrel portion through said channel and rendering said syringe non-reusable.

36. The syringe of claim 35 wherein said retaining means comprises a resilient annular flange defined by said plug member, said walled chamber has a first annular wall portion extending about a rearward portion thereof and a second wall portion extending about a forward portion thereof, said shoulder being disposed between said first and second wall portions, said resilient flange being disposed in a flexed disposition and bearing against said first wall portion in said chamber when said plug members in said rearward position, extending radially outwardly from said plug member in an unflexed disposition within said enlarged diameter portion of said chamber when said plug member is in said second forward position and, upon said piston being retracted within said barrel portion toward said one end thereof when said plug member is in said forward position, said flange bears against said shoulder, sealing said fluid flow channel.

37. The syringe of claim 35 wherein said piston rod defines an enlarged portion at the forward end thereof, said portion being received and held within a correspondingly configured recess in said piston such that upon said plug member being disposed in said forward position of said barrel portion and said piston being retracted within said barrel, a vacuum is created between said piston and said plug member causing said enlarged portion of said piston rod to be pulled from said recess, rendering said piston rod incapable of further reciprocation of said piston.

38. The syringe of claim 35 wherein said fluid flow channel comprises a plurality of fluid flow passageways, said passageways extending through and being spaced equidistantly apart about said shoulder.