Pump leakage has become more critical in recent years because of environmental concerns, fugitive emissions, handling of carcinogen materials and loss of valuable products. Acid based fluids typically have viscosities similar to water, and may have no or limited lubricity properties. Internal gear pumps or external gear pumps work best with Newtonian type fluids. Shear sensitive fluids are not a good application for gear pumps. The complete list of shear sensitive fluids is endless. Fluids that provide good fluid film between bushings and idler pin have best results with gear pumps. Acid based fluids also may not be compatible due to materials of construction and seals supplied with gear pumps. VIKING Pumps has a stainless liquid vane pump (LVP) for light weight fluids and a non-metallic mag drive external gear pump (CMD) for hazardous fluids that have Newtonian properties and require (leak free) seal-less operation.
As advised above, water based fluids with no lubricity will cause short pump life due to the fluid not providing an adequate film between the bushings and idler pin. Fluids with heavy and large solids will also cause short life for wear to gear pump internals. If fluid suction strainers can be used and if fluid has some lubricity gear pumps will provide positive flow and long life.
Centrifugal pumps with non-clog impellers are typically best pump for high trash fluids.
NPSH (Net Positive Suction Head) is critical for proper operation of any positive displacement pump. Net Positive Suction Head (NPSH) can be defined as two parts:
NPSH Available (NPSHA): The absolute pressure at the suction port of the pump.
NPSH Required (NPSHR): The minimum pressure required at the suction port of the pump to keep the pump from cavitating.
NPSHA is a function of your system and must be calculated, whereas NPSHR is a function of the pump and must be provided by the pump manufacturer. NPSHA MUST be greater than NPSHR for the pump system to operate without cavitating. Put another way, you must have more suction side pressure available than the pump requires.
Please see VIKING Pump website reference document UNDERSTANDING NET POSITIVE SUCTION HEAD for more detailed explanation.
Our inside engineering staff or myself or our other area representatives can assist with proper pump selection and application design.
