A screw pump, also known as a "water screw", is a positive-displacement (PD) pump that use one or several screws to move fluids or solids along the screw(s) axis. The term ‘screw pump' is often used generically. However, this generalization can be a pitfall as it fails to recognize the different product or ‘screw' configurations, as well as the uses, advantages and design considerations for each. The design differences of each screw configuration and pump type make each suitable for different applications and handling fluids with varying characteristics.
A screw pump is a type of rotary pump which is equipped with screws that mesh together and rotate within a cylindrical cavity or liner. The fluid enters from the suction side of the pump and moves linearly along these intermeshing screws to the discharge side of the pump. The clearances between the screws and the liner are very small hence the fluid gains pressure while moving through the pump.
As the gears rotate they separate on the intake side of the pump, creating a void and suction which is filled by fluid. The fluid is carried by the gears to the discharge side of the pump, where the meshing of the gears displaces the fluid. The mechanical clearances are small— in the order of 10 μm. The tight clearances, along with the speed of rotation, effectively prevent the fluid from leaking backwards. A Screw Pump is a type of Positive Displacement Pump. This means that it moves fluid by continually displacing the area that the fluid occupies. The screws are encased inside of a liner, usually made of some sort of metal. The fluid fits into the screw cavities within this liner and is forced through the pump and out of the discharge as the screws rotate and inter-mesh.
There are many uses for screw pumps in a variety of different industries, including Manufacturing, Mining, and Oil & Gas. Most of these applications deal with high viscosity fluid, such as oil or asphalt, or multi-phase fluid, which means there is liquid and vapor mixed together in the fluid stream.