Displacement Pumps: Screw Pump

What is a Screw Pump?

rotary, positive displacement screw pump

Screw Pump

A Screw Pump is a rotary, positive displacement pump that can have more than one screw to transfer high or low viscosity fluids along an axis.

Single Screw

A single screw rotary pump is also known as a progressive cavity or PC pump. The single screw pump consist of only one movable component called the rotor. The rotor turns inside a stater which causes cavities or voids. These voids move axially from the suction to the discharge. When the pump is primed, the cavities are filled with fluid which is carried up the casing to the discharge. PC pumps provide high suction, extremely low sheer, smooth pulsation free operation which is very important where turbulence can effect the fluid composition. A motor is used to turn the rotor. Because of the operating characteristics of the rotor a universal joint is needed to connect the drive shaft to the rotor. Universal joints, or U Joints, are flexible, mechanical connectors used to transmit rotary motion from one shaft to another shaft. That is not aligned with the first or when the alignment varies during service. The bearing housing is located on the drive shaft end of the pump. Large bearings protect the drive shaft as it turns.

Multi-Screw

A multi-screw pump can be used in a variety of applications. They can be designed with either two or three motors. A twin screw pump is designed to handle just about any type of fluid. They also provide a very high flow rate, and excellent suction. One rotor is right handed thread, and the other is left handed thread. There is a set of external timing gears and bearings which allows the rotors to turn simultaneously without touching. Because the rotors do not make contact at any time, the pump is able to run empty without causing damage to the system. In this type of pump, the fluid enters and is drawn along the screws. The screws has a very close tolerance to the body. Each screw thread is the same so they carry a specific volume of fluid to the discharge. The three screw pump has one power rotor and idler rotors. Unlike the twin screw, the three rotors do make contact with each other during operation. This makes it similar to the single screw pump, in that it operates with a continuous pulsating free flow.