Progressing Cavity Pumps
A progressive cavity pump is a type of positive displacement pump and is also known as a progressing cavity pump, progg cavity pump, eccentric screw pump or cavity pump. It transfers fluid by means of the progress, through the pump, of a sequence of small, fixed shape, discrete cavities, as its rotor is turned.
progressive cavity pumps are fundamentally fixed flow rate pumps, like piston pumps and peristaltic pumps, and this type of pump needs a fundamentally different understanding than the types of pumps to which people are more commonly introduced, namely ones that can be thought of as generating pressure. This can lead to the mistaken assumption that all pumps can have their flow rates adjusted by using a valve attached to their outlet, but with this type of pump this assumption is a problem, since such a valve will have practically no effect on the flow rate and completely closing it will involve very high pressures being generated. To prevent this, pumps are often fitted with cut-off pressure switches, rupture discs, or a bypass pipe that allows a variable amount of a fluid to return to the inlet. With a bypass fitted, a fixed flow rate pump is effectively converted to a fixed pressure one.