Piston pump having a variable stroke

Claim 1

A PUMP FOR USE AS A METERING DEVICE AND COMPRISING A CYLINDER AND A COACTING PISTON, CONDUIT MEANS ADAPTED TO RECEIVE A SUPPLY OF FLUID UNDER PRESSURE, A FIRST PRESSURE-REDUCING MEANS, A SECOND PRESSURE-REDUCING MEANS, AN INLET VALVE MEANS AND AN OUTLET VALVE MEANS FOR SECOND CYLINDER, SAID INLET VALVE MEANS CONNECTED TO BE SUPPLIED WITH FLUID THROUGH SAID FIRST PRESSURE-REDUCING MEANS FROM SAID CONDUIT MEANS, SAID PISTON WHEN MOVED IN ONE DIRECTION IN SAID CYLINDER ADAPTED TO INDUCE FLUID INTO SAID CYLINDER THROUGH SAID INLET VALVE MEANS TO PROVIDE AN INDUCTION STROKE, AND SAID PISTON WHEN MOVED IN THE OPPOSITE DIRECTION IN SAID CYLINDER ADAPTED TO EDUCE FLUID FROM SAID CYLINDER THROUGH SAID OUTLET VALVE MEANS TO PROVIDE A WORKING STROKE, BIASING MEANS ACTING ON SAID PISTON TO EXERT THEREON A FORCE FOR PRODUCING SAID INDUCTION STROKE, SAID BIASING MEANS SUCH THAT THE FORCE IT PRODUCES DECREASES PROGRESSIVELY DURING SAID INDUCTION STROKE, MEANS FOR ALTERNATELY APPLYING THE PRESSURE OF A CONTROL FLUID AND THE PRESSURE OF AN OPERATING FLUID TO SAID PISTON IN OPPOSITE TO SAID BIASING MEANS, SAID OPERATING FLUID DERIVED FROM THE SUPPLY OF FLUID UNDER PRESSURE IN SAID CONDUIT MEANS, SAID CONTROL FLUID DERIVED FROM SAID OPERATING FLUID THROUGH SAID SECOND PRESSURE-REDUCING MEANS, THE LENGTH OF SAID INDUCTION STROKE TO BE DETERMINED BY EQUILIBRIUM OF THE FORCE EXERTED BY SAID CONTROL FLUID AND THE FORCE PRODUCED BY SAID BIASING MEANS, THE PRESSURE OF SAID OPERATING FLUID SUCH THAT THE RESULTANT OF THE FORCES ACTING ON SAID PISTON PRODUCES SAID WORKING STROKE, AND N CONTROL MEANS FOR VARYING THE PRESSURE OF THE CONTROL FLUID WHEREBY TO VARY THE LENGTH OF SAID INDUCTION STROKE.