Screw Pump

What is a screw pump?

A screw pump is a rotary pump which is a form of a positive displacement pump and it delivers a known quantity of fluid for every revolution.

What are the parts of a screw pump?

A screw pump is made up of various components such as; a casing, a screw (depending on the type of screw pump; it can contain 1 screw up to 5 screws), bearings, a seal, a motor adapter and a drive shaft. Screw pumps are quite simple in construction.

How does a screw pump work?

The screw pump, as the name implies, the form of the screw is similar to a screw thread and hence by rotating it, the fluid moves along the screw thread from the suction side to the discharge side of the pump. Due to very close clearances inside the pump, the volumetric efficiency is high especially with viscous fluids as this reduces the amount of slippage of the fluid from the high pressure to the low pressure side. The pump itself like any positive displacement pump does not produce pressure, it only moves fluid but it is the actual system which produces back pressure due to friction loss.

What are the applications and uses of screw pumps?

Screw pumps are mostly used on fluids of a higher viscosity, moving these fluids with screw pumps results in an energy efficient and a relatively compact machine when compared to other pump types i.e centrifugal pump. For screw pumps with more than 2 screws, they are normally used on lubricating fluids only because the screws are not geared together and are relying on the fluid to lubricate the screws.

With a twin screw pump, the screws are geared which prevent the screws contacting each other and can therefore be used on non-lubricating fluids, chemicals and food-stuffs etc Twin screw pumps are capable of a higher flow rate than higher screw pump types i.e more than 2 screws.

The main applications for a screw pump are oil-based fluids, tar bitumen, adhesives (industrial type), chemicals and dairy products.

What are the different types of a screw pump?

There are various types of a screw pump depending on the number of screws – 1 screw up to 5 screw variations with the 2 screw pump (also called the twin screw pump) being the most common where the gears must be together to prevent contact. The twin screw pump can be fairly forgiving in terms of being able to handle entrained air or gas, including slugs of gas, whereas the 3 screw pumps cannot be used in this instance as there is a real chance that the screw would touch together.

When there is more than 1 screw involved, it is often referred to a Multi screw pump. The construction is relatively simple and is capable of a higher flow rate. They can also be used in self-priming applications with the correct suction piping configuration.