For applications involving the transfer of fuels, oils and other lubricating fluids, screw pumps and gear pumps are usually the pumping technology selected. Unlike water based liquids, changes in the temperature often result in a change in the viscosity of these types of fluids. As fluctuations in the thickness of a fluid affect the performance of a centrifugal pump much more than a positive displacement pump, screw pumps and gear pumps are generally the most efficient solutions for oils and fuels.
Whilst a gear pump is a more than acceptable option for the handling of lubricating fluids, the design of the screw pump has several advantages over it. Gear and screw pumps are two forms of positive displacement pumps that are used for specific purposes.
Advantages of screw pump
• Slow Speed, Simple and Rugged design
Probably the main and overall advantage of a screw pump is its superb reliability. The simple design, open structure and slow rotation speed makes it a heavy duty pump with minimal wear that operates for years without trouble.
• Pumps raw water with heavy solids and floating debris
Because of the open structure and large passage between the flights a screw pump can pump raw sewage without the need for a coarse screen before the pump. Both floating debris and heavy solids are simply lifted up. This saves considerably on equipment costs for a coarse screen or maintenance!
• Can run without water
A screw pump can operate even when there is no water in the inlet. Therefore it is not necessary to install expensive measures (level control etc) to prevent ‘dry-running’’. The lower bearing does not need cooling.
Advantages of Gear Water Pumps
• Controlled pumping action
A gear water pump can handle fluids that are too viscous for a centrifugal pump. The pumping action is very controllable and mathematical: if you double the speed, you double the output.
• Low speed
The output of a gear water pump is independent of discharge pressure. Since a gear pump doesn’t have to generate centrifugal force, it can be run at a much lower speed. This makes it smoother and more controllable.
• The best BEP
Gear pumps are self-priming, which can be a huge benefit. Their discharge pressure can be very high, dependent upon a number of factors. Gear water pumps don’t have a BEP or best efficiency point; they are consistently efficient.
Positive displacement pumps are of great use for industrial purposes. Determine your requirement properly and get the suitable pump.