Control apparatus for a positive displacement reciprocating pump

A positive displacement reciprocating pump for conveying a liquid or gaseous fluid, and comprising

• a fluid enclosure,
• movable piston means sealably disposed in said enclosure and dividing the enclosure into a pumping chamber on one side of the piston means and an actuating chamber on the other side thereof,
• an inlet valve and a separate outlet valve each communicating with said pumping chamber,
• control means for intermittently supplying a pressurized working fluid to said actuating chamber so as to intermittently move said piston means in a direction toward said pumping chamber and thereby discharge the conveyed fluid from such chamber, said control means including a source of pressurized working fluid, a working fluid line extending between said source and said actuating chamber, valve means operatively connected to said working fluid line and including a slide which is movable between an open position wherein said line is opened to discharge tank means to release the pressure therein, and a closed position wherein the pressure of said working fluid is maintained in said line and delivered to said actuating chamber, and pre-control means controlled by the position of said piston means for effecting movement of said slide to said open position upon said piston means essentially reaching its maximum movement toward said pumping chamber, and for moving said slide to said closed position upon said piston means essentially reaching its maximum movement in the opposite direction, said pre-control means including spring means for biasing said slide of said valve means toward its closed position, and pre-control valve means for periodically biasing said slide toward its open position, said pre-control valve means including a valve housing extending along a direction aligned with the direction of movement of said piston means, a rod having a control collar fixed thereto slideably mounted in said valve housing, and means operatively interconnecting said piston means and said rod, a first line extending between said valve housing and the side of said slide opposite said spring means, a second line extending between said valve housing and said source of pressurized working fluid, a third line extending between said valve housing and said discharge tank means, and wherein said rod and control collar are movable between a neutral position closing said first line, a position on one side of said neutral position wherein communication is opened between said first and second lines so that the pressure of said working fluid acts to bias said slide toward its open position, and a further position on the other side of said neutral position wherein communication is opened between said first and third lines so that the biasing force applied to said slide toward its open position is released.