ATMOSPHERE: A unit of measure equivalent to the absolute pressure at sea level of 14.7 PSI.

BARREL: In the petroleum industry, a unit of measure equivalent to 42 U.S. gallons.

BRINELL: Characterizes the indentation hardness of materials through the scale of penetration of an indenter, loaded on a material test-piece.

CENTIPOISE: An SI unit used to measure absolute viscosity (resistance to flow).

CAVITATION: The phenomenon of formation of vapor bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure.

HORSEPOWER: A British system measurement of work = 745.7 Watts.

KILOPASCAL: An SI pressure measurement. 100 Kpa = 14.5 PSI.

LAMINAR: Flow, sometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers.

MOHS: A scale measuring the relative hardness of minerals with a maximum value of 15 (Diamond).

NEMA: National Electrical Manufacturer’s Association, a self-regulating industry group for electric apparatus producers in the United States.

NEWTON: The unit of force derived in the SI system; it is equal to the amount of force required to accelerate a mass of one kilogram at a rate of one meter per second.

NEWTONIAN: A fluid whose viscosity is constant and is independent of shear rate; i.e., water or oil.

NPSHR: Net Positive Suction Head Required. The minimum amount of absolute pressure, measured in feet of water, required for a pump to deliver 98 percent of its theoretical capacity.

PSEUDOPLASTIC: Substances with no definite yield stress that exhibit a decrease in consistency with increasing shear rate.

ROTOR: A rotating part of a mechanical device, for example in an electric motor, generator, alternator or pump.

RUNOUT: The amount of radial variation in a rotation of a drive shaft.

THIXOTROPIC: A behavior that describes a type of non-Newtonian fluid whereby the viscosity shears dependent on both the amount of shear and the time applied

TURBULENT: A fluid regime characterized by chaotic, stochastic property changes.

VDMA: Verband Deutscher Maschinen- und Anlagenbau. A German Engineering Federation that publishes most of the specifications and standards for pump manufacturers in Europe.

WEIR: A “V” shaped or rectangular slot in the top of a water vessel, the height of which will indicated the flowrate in units of volume per unit of time.

This glossary of terms was contributed by Mike Dillon, president of seepex Inc (, a manufacturer of progressive-cavity pumps for delivering low to highly viscous, aggressive and abrasive media. Mr. Dillon has 36 years of experience in positive-displacement pumps and has authored more than 20 articles on the theory and operation of PD pumps.