The screw pump is usually classified as single-screw pump, twin-screw pump, three-screw pump and five-screw pump based on different quantities of rotors. Each screw pump has its own advantages, and therefore pump shall be selected according to the actual operating conditions, only by taking full advantages of their features we can achieve energy saving, materials saving, maximizing benefits or meeting some special requirements. As for the screw pump selection, we can proceed according to the following procedures:

The single-screw pump can transfer suspending liquid or special medium with metal particles or fibers. It is normally used to handle sewage and slurry, so the operating pressure of the pump is normally low and speed is lower to enlarge rubber stator life.

The twin-screw pump can transfer various medium in a wide viscosity range and in a large flow rate, for example, crude oil, residual oil, asphalt, heavy fuel oil etc., and it is also applicable for gas-liquid and solid-liquid mixtures. Normally the operating pressure of the pump and capacity are higher than single-screw pump, and manufacturing cost is more than single-screw pump. The change of viscosity is a decisive factor for speed selection of twin-screw pump, generally when medium viscosity is lower than 450 mm2/s, the speed of 1450 rpm can be selected, when medium viscosity is higher than or equal to 450 mm2/s, the speed of 950 rpm or even lower is recommended.

The three-screw pump, with maximum operating pressure up to 12 MPa, can transfer medium with good lubricating property, without solid particles and corrosive property. However the scope of medium transferred by the three-screw pump is limited, normally the medium with lubricating property is pumped well because two idler rotors are rotated directly by power rotor’ profile face without timing gears.

The five-screw pump features of a large unit flow section for its chamber, so that the pump capacity is larger, but the operating pressure is normally below 0.8 MPa. It is normally used for oil supply in special application where the mounting dimensions are limited like ship.

Sometimes, we may find the working conditions is applicable to several different screw pump selection, then we can select the most suitable pump type by considering price, installation, delivery time, maintenance.