Types of Screw Pumps
Screw pumps are available in a variety of different designs. Following are short descriptions of the most common types:
One Screw Pump - One screw pumps are referred to as Progressive Cavity Pumps, sometimes called PC Pumps or Worm Pumps. These are generally not considered in the Screw Pump family because the rotor used in these pumps is not shaped like a typical screw, but rather a twisted round shaft. A Progressive Cavity Pump has one shaft that is slightly twisted in the shape of a screw, and is housed in a pumping chamber that is usually rubber lined.
Two Screw Pump - The two screw pump, also known as the twin screw pump, is the most common type for high power applications such as heavy oil pipeline transfer. One of the screws is driven from the power source (motor, engine, etc.), and timing gears are usually incorporated to rotate the second screw.
Three Screw Pump -The three screw pump, also known as the triple screw pumps, is typically used for small applications, such as lubrication systems. One of the screws is driven from the power source, which then rotates the other two screws around it, without the use of timing gears.
Four Screw Pump - The four screw pump is essentially a Two Screw Pump, but with two screws per rotor, each facing opposite directions. The four screw pump sucks fluid in the suction port, then splits equally and is routed to both ends of the pump. The two fluid streams flow through the pump towards the middle and join together again before exiting the discharge port. Like the twin screw pump, the four screw pump has timing gears to drive the second rotor. Four screw pumps are often used in Multi-phase applications as well as oil transfer pipelines.
Five-Screw Pump - The five screw pump is primarily the same as a triple screw pump, but with 5 screws instead of 3. Like the three screw pump, the five screw pump has 1 diving rotor that drives all of the other screws. The five screw pump is often used in lube oil or hydraulic applications.
Screw pumps are sometimes designated as “Double Suction” or “Single Suction”. Double Suction Screw Pumps vs Single Suction Screw Pumps is another way of differentiating between Two Screw Pumps and Four Screw Pumps. Two Screw Pumps are a single suction design, having the fluid enter on one end of the pump and discharge from the other end. Four Screw Pumps are a double suction design, having the suction stream split to both ends and moving to a discharge in the middle.
The Working of a Screw Pump
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.