Application Xtra

Disc pumps

• Low NPSH requirements
• Suffers little damage or wear

A chemical processor located in the United Kingdom experienced considerable losses in a centrifuge feed of delicate and expensive crystal slurry. The progressing cavity pump was leaky and unreliable, causing damage to the final product. Rather than replacing the faulty pump with a conventional model, the company decided to install an ANSI standard disc-operated pump by Discflo Corp.

Disc pumps operate on boundary layer/viscous drag forces that produce a laminar flow with no pulsation. A boundary layer of fluid adheres to the discs as fluid enters the pump. As the discs rotate, kinetic energy is transferred through layers of fluid molecules passing between the discs, generating velocity and pressure gradients until the entire fluid mass is in motion. The fluid is then pulled through the pump in a smooth, laminar flow.

The ANSI disc pump installed in the centrifuge feed application operates the same way. While the pump meets or exceeds ANSI B73.1 standards, it is also capable of pumping severe abrasives with levels of viscosity and entrained air that are exceptionally higher than comparable pumps, says Discflo.

The ANSI disc pump is suitable for the crystal slurry application for several reasons. First, non-impingement pumping and laminar flow conditions provide suitable protection for shear-sensitive and delicate products. Second, laminar flow means low NPSHr (net positive suction head required). The NPSH requirements of a disc pump are about half to a third of that required by conventional pumps. Third, centrifuge feed applications are typically low flow and low NPSHa (net positive suction head available), thus cavitation is a big problem. The disc pump is less susceptible to cavitation because of its laminar flow and low NSPH requirements. When cavitation does occur, the pump’s boundary layer of fluid acts as a shock absorber.

For more information:

Discflo Corp, El Cajon, CA. Free info—Circle 240. www.rsleads.com/202df-240