Method of and apparatus for controlling of travel of the plunger in a dispensing pump chamber

In a finger operated pump for dispensing material from a container, said pump including a pump chamber, a cylindrical piston member having at least one horizontal cross-sectional portion with a central opening therein, disposed in said chamber for movement therein, a stem for moving said piston member downward having a discharge channel therein comprising a first upper portion of first outer diameter larger than said opening and a second portion of an outer diameter slightly smaller than said opening inserted through said opening, a stop at the bottom of said second portion of a size larger than said opening abutting against said horizontal portion when said pump is unoperated;

• a first spring acting against said stop and biasing said piston upward;
• first valve means at the bottom of said chamber for establishing communication between said chamber and the material to be dispensed in the container, said first valve arragned to close on initial actuation of said stem, and second valve means for establishing communcation between said chamber and said discharge channel in said stem, said second valve means being formed by cooperating portions of said second stem portion and said horizontal portion, said second valve means operable to establish communication between said channel and said chamber only after a predetermined movement of said stem downward, a method of improving the evenness of dispensing comprising interposing a second spring between said first stem portion and the top of said horizontal portion whereby during the initial actuation when said first valve is closed and said second valve opened said spring will be compressed prior to opening of said second valve and store energy to create a prepressurization in the stem mechanism which will result in smooth dispensing even if the stem is not smoothly actuated.