Abstract: Improvements in screw pumps, and especially positive displacement pumps, are disclosed. The clearance between the screw flight and the bore is increased over an increased period. The screw is balanced at preferred locations on the flight. Wear hard material such as tungsten carbide is emplaced on a portion of the outer surface of the screw flight. A wear measurement port extends from the outside surface of the pump to the inner surface of the bore. Pressure regulating ports and controls provide an active pressure feedback control system to control the feeding of pressure from the outlet end of the screw back toward the inlet end of the screw. Pump wear, and pressure pulsations in the operation of the pump are thus reduced. The wear measurement port enables a method of monitoring wear on the pump screw during operation without disassembling the pump, namely by manipulating a wear measurement device through the port. The wear measurement device can be a proximity sensor which can be connected to a monitor.