Syringe plunger assembly and barrel

  • US 6,090,077 A
  • Filed: 04/25/1997
  • Issued: 07/18/2000
  • Est. Priority Date: 05/11/1995
  • Status: Expired due to Term
First Claim
Patent Images

1. A syringe plunger handle assembly for use in a syringe barrel to inject fluid, comprising:

  • an elongated plunger formed with a longitudinally extending generally tubular wall defining a hollow interior along the length of the plunger, the plunger having a head end in front and a rear end portion with a thumb cap behind;

    the outer side of the wall at the head end has a plunger seal adapted to slide in sealed contact with a tubular wall when the plunger is moved within a syringe barrel;

    the wall at the head end of the plunger has a reduced diameter front portion extending forwardly beyond the plunger seal to a tip at the front of the plunger defining an opening within the front end portion leading into the hollow interior, the wall behind the tip having a stepped inner side surface comprising a land having an inwardly facing surface and a larger diameter portion extending behind the land into the hollow interior;

    a separate dislodgeable stopper slidingly held within the reduced diameter front portion of the plunger head by a holding force in excess of an expected fluid injection pressure force during use of the plunger in a syringe barrel, the stopper having a back end portion comprising a land and a reduced diameter front end portion extending a fixed distance forwardly beyond the tip, the stopper land having an outwardly facing surface in sliding sealed engagement with the inwardly facing surface of the land in the plunger wall, said lands comprising cooperating lands which apply said holding force to the stopper and seal the hollow interior of the plunger from said expected fluid injection pressure force; and

    the cooperating lands have sufficient length to allow the dislodgeable stopper to move said fixed distance back to the tip in sliding response to forward movement of the plunger after the front of the stopper contacts a stop, whereby said holding force is reduced by substantial disengagement of the cooperating lands in preparation for dislodgement of the stopper without unsealing the hollow interior of the plunger.

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