Stationary stem pump

A fluid dispenser comprising

• a reservoir containing a fluid,
• a piston chamber-forming member defining a chamber about a chamber axis, the chamber having a radially inwardly directed chamber wall, an inner inlet end and an outer open outlet end,
• the inlet end of the chamber for communication with the reservoir,
• the piston chamber-forming member including a center post member having an inner end and a distal outer end,
• a piston chamber-forming member including the chamber and the post member formed as a unitary element by injection molding with the inner end of the post member fixedly integrally attached to the piston chamber-forming member at the inlet end of the piston chamber-forming member with the post member extending along the axis coaxially of the chamber outwardly from the inner end of the post member to the distal outer end of the post member,
• the post member having a radially outwardly directed side surface which is generally circular in cross-section normal to the axis,
• an inlet one-way valve across the inlet end of the chamber permitting fluid flow outwardly but preventing fluid flow inwardly,
• a piston-forming element coaxially slidably in the chamber between a retracted position and an extended position,
• the piston-forming element having a hollow stem with a central passageway extending coaxially through the stem from an inner end of the stem to an outer end of the stem with the passageway forming a discharge opening at the outlet end of the stem,
• the passageway having a radially inwardly directed side surface,
• a disc extending radially outwardly from the stem with a circumferential radially outer distal edge for engagement with the chamber wall to prevent fluid flow therebetween outwardly and inwardly,
• an outward annular portion of the radially outwardly directed side surface of the post member engaging an inward annular portion of the radially inwardly directed of the side surface of the stem to prevent fluid flow inwardly therepast but permitting fluid flow outwardly therepast,
• the inward annular portion of the radially inwardly directed of the side surface of the stem being (a) resilient to deflect when pressure on an inner side thereof exceeds pressure on an outer side thereof to permit fluid flow outwardly therepast and (b) biased when deflected to return towards an unbiased condition in which engagement between the inward annular portion and the outward annular portion prevents fluid flow outwardly,
• in all positions of the piston-forming element relative the piston chamber-forming member between the retracted position and the extended position, the piston-forming element is coupled to the piston chamber-forming member with the passageway coaxially about the post member and the disc in the chamber with the outer distal edge of the disc engaging the chamber wall,
• whereby a compartment is defined in the chamber between the piston-forming element and the piston chamber-forming member enclosed by the one-way valve, the disc, the inward annular portion and the outward annular portion, which compartment has a volume which varies with relative axial sliding of the piston-forming element in the piston chamber-forming member between the retracted position and the extended position,
• wherein with sliding of the piston-forming element inwardly relative the piston chamber-forming member the volume of the compartment is reduced pressurizing fluid in the compartment to deflect the deflectable one of the inward annular portion and the outward annular portion such that fluid passes outwardly between the inward annular portion and the outward annular portion and outwardly in the passageway to exit the discharge outlet, and
• wherein with sliding of the piston-forming element outwardly relative the piston chamber-forming member the volume of the compartment is increased drawing fluid from the reservoir past the inlet one-way valve outwardly into the compartment.