Doc No: OMM50001254
Rev: A Page 43 of 47
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Glossary of Commonly Used Terms
CAPACITY
The total volume throughput per unit of time at
suction conditions. It includes both liquid and
any dissolved or entrained gases. For all
practical purposes this can be considered the
volume flow rate in the suction pipe. The
standard unit of pump capacity is U.S. gallons
per minute (GPM) and metric cubic meters per
hour (m3/hr).
CAVITATION
The state where fluid pressure drops below
vapor pressure, causing the liquid to begin to
change from a liquid to a gas and boil. Usually
occurs in the chamber between the suction and
discharge valves during the suction stroke, and
often sounds like a mechanical knock.
Cavitation results in the formation of gas
bubbles, or cavities, in the fluid that cause
vibration and damage to components when
they collapse.
DAMPENER
A device that reduces pressure pulsations in
the suction or discharge piping. This may be
referred to as a suction stabilizer, accumulator,
or surge suppressor.
DISPLACEMENT
The volume swept by all pistons or plungers
per unit time. This term is typically expressed
as gallons per revolution.
POWER END
The portion of the pump that converts supplied
rotary motion into linear motion used by the
Fluid End to move the pumpage.
MECHANICAL EFFICIENCY
Mechanical efficiency (ME) is the ratio,
expressed as a percentage, of pump power
output to the pump power input. The
mechanical efficiency of reciprocating pumps is
very high, typically 85% to 90%.
VOLUMETRIC EFFICIENCY
Volumetric efficiency (VE) is the ratio of actual
pump capacity output to theoretical
displacement. The volumetric efficiency is
affected by the fluid being pumped and the
discharge pressure.
