Abstract: A pump assembly for dispensing fluent material from within a container includes a tank and a piston defining therebetween a pump chamber and movable relative to each other to pump fluid from the container into and out of the pump chamber. A poppet interposed between the tank and the piston extends at one end thereof into the inlet conduit for the pump chamber and at the opposite end into the exhaust conduit. When the tank and piston are moving relative to each other to draw fluid from the container into the pump chamber, the end of the poppet extending to within the exhaust conduit engages against a valve seat defined in the exhaust conduit to close the exhaust conduit. The other end of the poppet extending to within the inlet conduit is frictionally engaged within the inlet conduit and the drag forces thus effected upon this end of the poppet operate to enhance the sealing effect of the opposite end of the poppet to close the exhaust conduit thereby permitting fluid to be drawn into the pump chamber.