A pump for dispensing liquid from a reservoir comprising: piston chamber-forming member having a chamber disposed about an axis, the chamber having a diameter, a chamber wall, an inner end and an open outer end, the inner end of the chamber in fluid communication with the reservoir, a one-way valve between the reservoir and the chamber permitting fluid flow through the inner end of said chamber, only from the reservoir to the chamber, a piston sleeve member slidably received in the chamber of the piston chamber-forming member for reciprocal axial inward and outward movement therein in a stroke of movement between an extended position and a retracted position, said sleeve member having an axially extending hollow sleeve stem having a central bore therethrough from an inner end to an outlet proximate an outer end, an outer disc on the sleeve stem and extending radially outwardly from the sleeve stem circumferentially thereabout to engage the chamber wall to form a seal therewith against fluid flow therepast, the outer disc having a cam surface annularly thereabout outwardly of the sleeve stem, a piston slide member having an axially extending hollow slide stem having a central passage closed at an inner end and open at an outer end, an inner disc on the slide stem extending radially outwardly from the slide stem circumferentially thereabout proximate the inner end of the slide stem, a spreader disc on the slide stem spaced axially outwardly from the inner disc and extending radially outwardly from the slide stem circumferentially thereabout, an inlet located on the slide stem between the inner disc and the spreader disc in communication with the passage, the slide member coupled to the sleeve member for limited coaxial sliding movement of the slide member relative the sleeve member between an extension condition and a retraction condition with the slide stem coaxially disposed relative the bore, the passage in communication with the bore, and the spreader disc located in the chamber inwardly of the outer disc, the inner disc engaging the chamber wall axially inwardly of the spreader disc to substantially prevent fluid flow in the chamber past the inner disc in an inward direction but with the inner disc elastically deforming away from the chamber wall to permit fluid flow in the chamber past the inner disc in an outward direction, the spreader disc having a camming surface in opposition to the cam surface of the outer disc, in the extension condition the camming surface of the spreader disc is axially spaced from the cam surface of the outer disc, in the retraction condition the camming surface of the spreader disc engaging the cam surface of the outer disc to urge the edge portion of the outer disc radially outwardly into the chamber wall. piston chamber-forming member having a chamber disposed about an axis, the chamber having a diameter, a chamber wall, an inner end and an open outer end, the inner end of the chamber in fluid communication with the reservoir, a one-way valve between the reservoir and the chamber permitting fluid flow through the inner end of said chamber, only from the reservoir to the chamber, a piston sleeve member slidably received in the chamber of the piston chamber-forming member for reciprocal axial inward and outward movement therein in a stroke of movement between an extended position and a retracted position, said sleeve member having an axially extending hollow sleeve stem having a central bore therethrough from an inner end to an outlet proximate an outer end, an outer disc on the sleeve stem and extending radially outwardly from the sleeve stem circumferentially thereabout to engage the chamber wall to form a seal therewith against fluid flow therepast, the outer disc having a cam surface annularly thereabout outwardly of the sleeve stem, a piston slide member having an axially extending hollow slide stem having a central passage closed at an inner end and open at an outer end, an inner disc on the slide stem extending radially outwardly from the slide stem circumferentially thereabout proximate the inner end of the slide stem, a spreader disc on the slide stem spaced axially outwardly from the inner disc and extending radially outwardly from the slide stem circumferentially thereabout, an inlet located on the slide stem between the inner disc and the spreader disc in communication with the passage, the slide member coupled to the sleeve member for limited coaxial sliding movement of the slide member relative the sleeve member between an extension condition and a retraction condition with the slide stem coaxially disposed relative the bore, the passage in communication with the bore, and the spreader disc located in the chamber inwardly of the outer disc, the inner disc engaging the chamber wall axially inwardly of the spreader disc to substantially prevent fluid flow in the chamber past the inner disc in an inward direction but with the inner disc elastically deforming away from the chamber wall to permit fluid flow in the chamber past the inner disc in an outward direction, the spreader disc having a camming surface in opposition to the cam surface of the outer disc, in the extension condition the camming surface of the spreader disc is axially spaced from the cam surface of the outer disc, in the retraction condition the camming surface of the spreader disc engaging the cam surface of the outer disc to urge the edge portion of the outer disc radially outwardly into the chamber wall.