PUMPS

Rotary positive displacement pumps provide an effective solution for the bulk transfer for liquids in the tank storage industry, where a wide range of flow viscosity is encountered. Brain Warshaw reviews US and European manufacturers who offer a range of pumps.

The rotary positive displacement pump is self-priming, efficient, relatively quiet, and can be operated using variable speed drives. It will handle lubricating, as well as nonlubricating products, providing they contain neither solid contaminants nor chemicals that could attack the internal components. Due to the type of construction, with close meshing, but not touching, helical spindles or vanes to drive the fluid, it is essential that the pumps should be protected with fine mesh strainers.

This review looks at a small selection of the many manufacturers in Europe and the USA who can provide a range of positive displacement rotary pumps. German pump manufacturer Allweiler AG was founded in 1860 and is part of the US's Colfax Pump Group, which also includes Houttuin BV, IMO, Warren, and Zenith Pumps as associates.

Amongst a varied range of pump types, Allweiler manufactures rotary positive displacement screw spindle pumps that are used in the oil and chemical industries as well as in power generation. Product Manager, JÙrgen Gebhard says the two and three-spindle screw pumps have special advantages in that they exhibit very good net positive suction head (NPSH) values, can run 'dry' for a short period of time, and move fuel, with low axial speeds.

The liquid is moved continuously, with virtually no pulsation or turbulence. New materials Gebhard explains that the direction of development at Allweiler has been towards pumps that exhibit lower pulsation action and shearing forces. Referring to the increasing demand for biodiesel, he says,,"We are developing and testing new materials, especially sealing materials, that will be useful for this market."

Allweiler's low pressure TRILUB series comprises a range of five, triple-spindle screw pumps capable of moving fluid at a rate of between 11 and 7,500 l/min. They are used to pump products ranging from distillate fuels to HFOs over a wide viscosity band of 2 to 1,500 mm2/s, and at a maximum operating pressure from 7 to 16 bars depending on the unit selected. The units are designed to function at a temperature of minus 20ÁC to plus 155ÁC, and will operate in any plane.

The model SN operates at the higher pressure of 100 bars, pumping fluids with viscosities of up to 5,000 mm2/s, and a flow rate to a maximum of 5,300 l/min. It can operate to an elevated temperature of 250ÁC.