Patent ID: 9388809
Filing Date: 2016-07-12
CPC Classification: F04C

Claim Text:
1. A multiple stage pump assembly comprising at least two pumps arranged in series, wherein at least the second and each subsequent pump comprises a pump inlet, a pump outlet, at least two threaded rotors and a pressure controlled valve, the pressure controlled valve being adapted to control re-circulation of fluid from the pump outlet to the pump inlet, said pressure controlled valve being one which responds to a ratio between the pressure at the pump outlet and the pressure at the pump inlet, such that the valve permits fluid to flow there-through when the ratio between the pressure at the pump outlet and the pressure at the pump inlet reaches a threshold, said pressure controlled valve comprising a piston having an inlet face and an outlet face, a surface area of the inlet face being greater than a surface area of the outlet face and a ratio between the area of the inlet face to the area of the outlet face prescribing the threshold ratio between the pressure at the pump outlet and the pressure at the pump inlet.