For many years now, centrifugal pumps have been the go-to pumping option for many fluid-transfer applications in different industries. Centrifugal pumps operate by drawing water into the pump impeller, which accelerates the water flow’s speed and then makes it flow outward into the volute discharge port. They are a perfect choice in the transfer of high liquid volumes and perform exceptionally well with less-viscous fluids pumped in pipe systems with varying flow rates.
However, positive displacement screw pumps are another excellent pumping technology that has proven to be relatively better than centrifugal pumps. They operate using two opposing screws that engage and create a sealed cavity with the surrounding pump enclosure. When the fluid enters the pump, the drive screws rotate and steadily move the fluid from the inlet toward the discharge port. The pump ensures a volumetrically steady flow rate no matter the amount of pressure applied. Their operating principle makes them a better choice for handling a wide range of liquids, including very viscous ones.
Some of the many benefits of screw pumps include:
• Ability to handle a wide range of liquids, viscosities, flow rates, and pressures
• High operating efficiencies, leading to low operational costs
• Superb suction capabilities
• Smooth running and quiet operation
• Low internal velocities
• Ensured constant fluid flow even with varying system backpressures
• Low mechanical vibration, which means less wear and tear
• High tolerance to entrained air and gases
• Excellent priming
• Low pulsation, which means low stress on the fluid transfer components
• Easy to install and maintain
• High tolerance to contamination compared to other rotary pumps
Two types of screw pump designs
There are two types of positive displacement screw pumps used in industrial applications: twin screw with timing gear (WTG) and triple screw.
The WTG pump is comprised of a timing-gear transmission and external bearings that are designed to produce a double-suction, self-priming process without creating any metal contact among the pump’s internal components. The WTG’s design enables it to offer consistent, very-high flow rates (more than any other positive displacement pump), even with varying liquid viscosity levels and system backpressures. The ability of screw pumps to offer higher flow rates as a fluid’s viscosity increases, compared to centrifugal pumps, makes them a better alternative for many transfer applications – even with lubricating, contaminated, aggressive, and highly viscous fluids.
The triple screw pump is designed with one male spindle and two female secondary spindles enclosed in a casing. Fluids move into the casing continuously and smoothly through an axial direction from the intake point to the outlet. This design delivers steady, smooth fluid flow with low energy consumption and noise levels. Triple screw pumps typically deal with lubricating fluids without suspended solids.