Discharge controlled reciprocating pumps

Claim 1

A discharge-controlled pump means comprising: a cylinder having a piston reciprocally received therein, and defining a compression chamber within said cylinder on one side of said piston; means for intermittently reciprocating the piston to decrease the volume of the compression chamber and means for alternately restoring the piston to a position wherein the volume of the compression chamber is increased; a fluid supply; reversible flow conduit means for forwarding fluid from the fluid supply to the compression chamber and for returning fluid from the compression chamber to the fluid supply; a discharge valve in communication with said compression chamber, and arranged for discharging fluid from the compression chamber when the piston has reached the vicinity wherein the volume of the compression chamber is at least nearly its smallest; pressure responsive means on said discharge valve for maintaining said discharge valve in a closed condition until the fluid pressure in said compression chamber increases to a predetermined threshold value; a normally open electromagnetic valve interposed in said conduit means; a controller interconnecting the normally open electromagnetic valve and the means for intermittently reciprocating the piston for controlling the electromagnetic valve in response to reciprotation of the piston, said controller being set to close the normally open electromagnetic valve only for a period of time beginning after the piston has begun to decrease the volume of the compression chamber but before the piston has reached the vicinity wherein the volume of the compression chamber is its smallest; and normally closed back pressure relief valve means interposed in said conduit means between said electromagnetic valve and said fluid supply, said back pressure relief valve means having a threshold pressure for opening which is lower than the threshold pressure for opening said discharge valve; said compression chamber being so arranged that, upon reciprocation of said piston to decrease the volume of the compression chamber, the threshold pressure for opening the normally closed back pressure relief valve is reached before said normally open electromagnetic valve is closed by said controller; whereby a controlled amount of fluid is present in the compression chamber when the normally open electromagnetic valve is closed by said controller, so that a controlled amount of fluid may be expelled from the compression chamber through said discharge valve, upon further reciprocation of the piston in a sense to decrease the volume of the compression chamber.