Multi-stage pump assembly having a pressure controlled valve for controlling recirculation of fluid from the pump stage outlet to the pump stage inlet

摘要

Pump having a pump inlet, a pump outlet, at least two threaded rotors and a pressure controlled valve. The pressure controlled valve is capable of controlling re-circulation of fluid from the pump outlet to the pump inlet. The pressure controlled valve can be a control valve. A multiple stage pump assembly is also provided having least two pumps arranged in series, in which at least one of the pumps is the aforementioned pump.