Disposable plastic liquid pump

A pump for dispensing liquids from a reservoir, comprising:

• (a) a piston-chamber forming element having a cylindrical chamber, said chamber having a chamber wall, an outer open end and an inner end in fluid communication with the reservoir;
• (b) one-way valve means between the reservoir and the chamber permitting fluid flow through the inner end of said chamber, only from the reservoir to the chamber;
• (c) a piston forming element slidably received in the chamber extending outwardly from the open end thereof;
• said piston forming element being generally cylindrical in cross-section with a central axially extending hollow stem having a central passageway open at an outer end forming an outlet and closed at an inner end;
• a circular flexing disc extending radially outwardly from the stem proximate the inner end, the flexing disc having an elastically deformable edge portion proximate the chamber wall circumferentially thereabout,
• a circular sealing disc extending radially outwardly from the stem spaced axially outwardly from the flexing disc, the sealing disc engaging the chamber wall circumferentially thereabout to form a substantially fluid impermeable seal therewith on sliding of said piston forming element inwardly and outwardly,
• an inlet located on the stem between the flexing disc and sealing disc in communication with the passageway via a short channel extending radially inward from the inlet to the passageway,
• engagement means on said stem outward of the chamber forming element for engagement to move the piston forming element inwardly and outwardly,
• locating means on said stem extending radially outwardly from the stem to engage said chamber wall and guide the piston forming element in sliding axially centered and aligned within the chamber,
• the locating means comprising a plurality of axially extending webs,
• wherein in operation,
• (i) on the piston forming element sliding outwardly in said chamber, the flexing disc substantially preventing fluid flow past the flexing disc in an inward direction, and
• (ii) on the piston forming element sliding inwardly into the chamber the flexing disc elastically deforms away from the chamber wall to permit fluid flow past the flexing disc in an outward direction.