Material dispensing device including a metering chamber

Claim 1

A MATERIAL DISPENSING DEVICE TO WHICH MATERIAL TO BE DISPENSED IS SUPPLIED UNDER PRESSURE, COMPRISING AN ENCLOSED METERING CHAMBER HAVING AN INLET AND AN OUTLET THROUGH WHICH MATERIAL IS DISPENSED, A PISTON DISPOSED IN SAID CHAMBER AND SHIFTABLE THEREIN TO DISPENSE MATERIAL THROUGH THE OUTLET, VALVE MEANS CONTROLLING THE ADMISSION OF MATERIAL TO THE CHAMBER AND THE DISCHARGE OF MATERIAL THROUGH SAID OUTLET, SAID VALVE MEANS SELECTIVELY OPERABLE TO ALTERNATIVELY BLOCK THE FLOW OF MATERIAL TO THE CHAMBER WHILE OPENING SAID OUTLET AND ADMIT MATERIAL TO THE CHAMBER WHILE CLOSING SAID OUTLET, SAID PISTON RESPONSIVE TO THE PRESSURE OF INCOMING MATERIAL THEREAGAINST TO BE SHIFTED TOWARD THE OUTLET THEREBY DISPENSING MATERIAL FROM THE CHAMBER WHEN THE OUTLET IS OPEN, MOTIVE MEANS COUPLED TO SAID VALVE MEANS TO OPERATE THE SAME, AND A MATERIAL CONDUCTING PASSAGE COMMUNICATING WITH SAID OUTLET AND EXTENDING THEREBEYOND, SAID VALVE MEANS INCLUDING A PORTION SHIFTABLE INTO SAID PASSAGE UPON OPENING OF SAID OUTLET AND RETRACTABLE FROM THE PASSAGE UPON CLOSING OF THE OUTLET TO INCREASE THE EFFECTIVE VOLUME OF THE PASSAGE AND PREVENT DROOLING OF MATERIAL THEREFROM WHEN SAID OUTLET IS CLOSED.