Abstract: A fluid pump dispenser of the loss motion piston type provides for maintaining the discharge open a slight interval at the commencement of each plunger upstroke while the pump chamber expands to retract product from the discharge passage into the chamber to thereby avoid the formation of product droplets at the exit end of the discharge. Such is effected in accordance with one embodiment by reducing the friction force acting between the piston and the pump cylinder relative to the friction force acting between the piston and the stem. In another embodiment an inlet valve assembly has a portion lying in the path of the piston which portion is connected by spring legs to a valve portion such that the restoring force of the spring legs shifts the piston together with the stem at the commencement of the plunger upstroke which maintains the discharge passage in open communication with the chamber.

Abstract: A fluid pump dispenser has a pump body including a pump cylinder defining a pump chamber with a valve controlled product inlet passage leading to the chamber, a manually reciprocable pump plunger having a hollow stem defining a discharge passage leading from the chamber, a pump piston mounted on the inner end of the stem for relative sliding movement, the body having a plunger return spring for biasing the plunger into a raised position, the piston being limited for relative sliding movement between discharge open and closed positions, the piston having an annular projection defining a discharge valve seated in an annular groove of a plug element fixedly mounted to the stem at its inner end. A lost-motion effect is created between the piston and the stem which closes the discharge valve during the pressure stroke and opens the discharge during the intake stroke.