Positive Displacement Pumps Are Not Created Equal

There are significant differences between PD pump types. Improper pump selection can cost operators:

This table provides an overview of several types of leading positive displacement pumps:

PD Pump	Features	Viscosity Range	Flow Range
Sliding Vane	Exceptional for thin liquids due to direct contact of vanes to casing and minimal internal clearances Excellent on thick liquids at slow speeds Exceptional efficiency at low flow rates Excellent suction lift and line stripping capabilities Self-adjusting vanes eliminate energy-robbing slip and capacity loss to provide substantial energy savings High mechanical efficiency = energy savings Differential pressure to 200 psi Speed to 3,600 RPM Hydrodynamic journal bearing models significantly reduce friction, excessive heat build-up and energy loss Motor speed models are specifically designed for continuous duty operation for low and medium viscosity applications Low energy consumption	Very thin (LPG, Refrigerants, Solvents, Fuel Oils, Gasoline, Liquid Carbon Dioxide, Ammonia, etc.) to High viscosities up to 50,000 cSt	1 to > 2,000 GPM
Internal Gear	Differential pressure to 200 psi (higher pressures are attainable) Speed to 3,600 RPM Metal-to-metal gear results in wear and slip, resulting in efficiency degradation and higher energy consumption over time	High viscosities up to 1,000,000 cSt	0.5 - 1,500 GPM
External Gear	Do not perform well under critical suction conditions, especially with volatile liquids Good for high pressure applications such as hydraulics Differential pressure to 3,000 psi + Speed to 3,600 RPM Metal-to-metal gear design subject to efficiency degradation Must be rebuilt or replaced No clearance adjustments for wear which results in slip, efficiency degradation and higher energy consumption	High Viscosity up to 1,000,000 cSt	Drops per minute to 1,500 GPM
Lobe	Used frequently for food-type products due to sanitary nature and ease of cleaning Vertical drain port reduces efficiency by 15-20% Sanitary Models: Differential pressure to 200 psi Non-Sanitary Models: Differential pressure to 400 psi	Low Viscosity with diminished performance up to 1,000,000 cSt	5 - 3,000 GPM
Air Diaphragm (AODD)	No bearings or rotating shaft Can handle a wide range of shear-sensitive, abrasive and non-abrasive liquids as well as solids High pressure operation can cause excessive wear around valve seats as the check valve closes Variable speed flow operation Requires air compression system. Electricity is used to run compressors. Energy accounts for 70% of compressed air life cycle cost – air is not free. High energy costs.	Medium viscosity to 26,000 cSt	1 - 500 GPM