1. IN A PUMP, A STACK-UP OF PARTS INCLUDING A RING PART HAVING A CONTOURD BORE FORMING A PUMPING CHAMBER, FIRST AND SECOND PORTED PRESSURE PLATE PARS ON OPPOSITE SIDES OF SAID RING AND FORMING INLET AND OUTLET AREAS COMMUNICATING WITH THE INTERIOR OF SAID RING PART, A VALVE PLATE PART CARRYING A FLOW CONTROL VALVE INTEGRALLY THEREWITH AND HAVING A DISCHARGE PASSAGE FOR RECEIVING THE DISCHARGE OF THE PUMP AND DIRECTING A CONTROLLED FLOW OUTWARDLY, SAID VALVE PLATE PART AND SAID FLOW CONTROL VALVE FORMING A SINGLE UNIT, A SEPARATOR PLATE PART BETWEEN SAID VALVE PLATE PART AND ONE OF SAID PRESSURE PLATE PARTS TO REGULATE THE INLET AND OUTLET AREAS, AND RETAINING MEANS ALIGNING AND RETAINING SAID PARTS IN ASSEMBLY WITH ONE ANOTHER, A NOTCHED ROTOR IN SAID RING PART HAVING A SLIPPER MEANS