Growing Applications for Screw Pumps

As complexity has grown in processes and new conditions have been added, screw pump technology has attracted increased interest from facility designers, process engineers and operators across the industry.To get more news about NETZSCH Pump Accessories, you can visit hw-screwpump.com official website.

The need to improve energy efficiency and operating flexibility while driving down operating costs is the main goal. It is time to revisit conventional approaches to pump selection and take a look at the evolution of screw pumps, determine how they could improve economics and safeguard the vitality of critical processes in process plants and transfer systems. This article focuses on pump types with multiple screws. All screw pumps are part of the positive displacement family and, as such, are designed to displace flow in direct proportion to the rotary speed of the pump. This runs contrary to hydrodynamic pumps, which rely on kinetic energy.

The tight cavities are formed when the profiles of the screws mesh as the pump rotates, thereby transporting fluids from suction to discharge as it builds up pressure to overcome the downstream back pressure from the system. The screws of the pump are the main pumping elements, where the driven screw or power rotor transfer the torque to one or several idler screws mechanically and hydraulically. The smooth opening and closing pump cavities result in a pump flow with low pulsations and airborne noise.
Most screw pumps are designed to eliminate axial hydraulic thrust either by using balance pistons or by having the screws in an opposed flowing arrangement. The absence of thrust bearings helps to simplify the pump design and eliminate potential wear and maintenance areas.

Applications
Most multiple-screw pump designs are self-priming and can work with low suction pressure. They are also gas tolerant and able to handle free and entrained gases without vapor locking. Low internal fluid velocity and the gentle meshing of the rotors also contribute to low shear rates, which is especially important for shear-sensitive, non-Newtonian fluids as well as different kinds of emulsions.

The operational flexibility of the multiple-screw pump is manifested by its ability to work over a large viscosity range, from light hydrocarbons to residues and emulsions. The screws are normally case hardened for improved wear resistance, and customized coatings are occasionally used to protect rotor bores, the rotor liner and pump casing.

Today’s family of screw pumps includes designs that were traditionally used in hydrocarbon processing. Applications are now increasingly found in the chemical, petrochemical, food and biofuel industries. Each pump design has its specific set of operational advantages and possibilities. Finding the right type of pump for specific applications is not only important for the process but also a cost optimization opportunity including the total cost of ownership.

Designs
Two-screw pumps without timing gears:

One pump design relies on two screws, one drive and one driven idler screw, which are radially supported by bushings and lubricated by the pumped fluid. The bushings are also part of the axial thrust balance configuration where discharge pressure on one side of the journal and suction pressure on the other side creates a pressure balance while providing liquid for lubrication and cooling.

The torque transfer from one screw to the other happens by means of a rolling (as opposed to sliding) contact over the screw profile, providing good wear resistance. These screws are running with radial clearance to the bores, which makes this pump design resistant to abrasive wear and suitable for fluids with low lubricity.

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