Volumetric metering pump

Claim 1

An improved volumetric liquid metering pump to deliver uniformly and continuously with very high precision limited quantities of liquid, said pump comprising in combination: a. first and second parallel cylinders; b. first and second identical pistons reciprocable in said first and second cylinders respectively, the ratio of length to diameter of said pistons being between 2:1 and 100:1; c. a slidable member carrying said pistons which extend parallel to each other and in opposite directions thereupon, with attachment means connecting the first and second pistons with the slidable member and forming a rigid body; d. a rack on said slidable member; e. a pinion engaging said rack forming the sole driving means for the slidable member; f. a stepping reversing motor operatively connected to rotate said pinion; g. a fixed valving member; h. a valving member movable with respect to said fixed valving member between first and second pumping positions and forming with said fixed valving member a valve assembly; i. a pair of solenoids effective to move said movable valving member between said first and second pumping positions; j. a pair of conduit means connecting each cylinder separately to said valve assembly; k. liquid inlet means and liquid outlet means connected to said valve assembly; l. passage means in said valve assembly connecting said inlet means to one of said conduit means and said outlet means to the other of said conduit means when said movable valving member is in said first pumping position, and connecting said outlet means to said one conduit means and said inlet means to said other conduit means when said movable valving member is in said second pumping position; m. a pulse generator effective to operate said motor in equal pulsed jerks; n. a pair of limit switches, one at each end of the travel of said slidable member, and operated by said slidable member effective to actuate said solenoids to move said valving member from one of its pumping positions to the other, and effective to reverse the direction of operation of said motor, at the end of each stroke of said pistons; and o. delay means effective to insure that said limit switches can operate only in an interval between two consecutive jerks.