The heart of this unit is a precision, long-life radial-piston pump controlled upon demand by an integral pressure switch. This switch is infinitely adjustable from the minimum to the maximum operating pressure. Automatic pressure control is assured, because the pump restarts if pressure drops. Clamping pressure is assured even with an electrical power failure since the solenoid valves are mechanically held in "clamped" position, requiring power only to unclamp. The poppet design of these valves ensures positive, leak-free sealing.