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The following definitions are intended to give basic understanding of the terms
commonly used in the pump industry. Some industry standards, or customer
specifications, may have specific meaning of certain terms that may be different
from their common usage - in such case the terms should be interpreted in the
context of the standards, or specifications, being referred to.
Can pump -
Cantilever pump - a pump whose impeller is cantilevered from its bearing
assembly, or a pump with only one bearing housing assembly as opposed to a
pump which has two bearing housing assemblies mounted on opposite sides of
the pump casing. A cantilever pump, which typically is also a radial split pump,
can be either a horizontal or a vertical pump. It is also known as overhung pump.
Carbon steel –
Carbonate solution -
Cartridge seal - A self-contained mechanical seal assembly, including the seal,
sleeve, gland, mating ring, etc., that is pre-assembled and preset for installation
as a unit.
Case - the pressure-containment part of a pump that has the volute (or diffuser)
chamber that encloses the impeller, or impellers. The case can be axial or radial
split. For radial split case, a cover is required to complete the pump casing.
Case crowning - refers to the method or style of machining the horizontal split-
line surface of the upper half case of a horizontal pump with a very small angle,
or taper. The purpose of case crowning is to transfer a higher amount of the bolt
load towards the case bore to pinch the case gasket and prevent washout
especially around the volute areas.
Case liner -
Case retiring thickness - the minimum thickness in which a pump casing has
to be replaced, or retired, due to loss of metal thickness caused by erosion or
corrosion over a period of time.
Case ring -
Case separating ring –
Casting cleaning -
Cast iron -
Centrifugal force –
Centrifugal pump -
Certified material test report (CMTR) –
Certified test –
Choke ring – see bull ring.
Chrome plating -
Cleaning – see casting cleaning
Close-coupled pump - a pump whose impeller is mounted directly on the
driver shaft. The driver is designed with a special extended shaft to
accommodate the impeller. Close-coupled pumps are popular for its small
footprint and light weight but are limited in sizes. See flexible-coupled pump.
Closed impeller - an impeller with two shrouds or disks; on front and back side
- which enclosed the vanes; also referred to as enclosed impeller.
CO2 pump -
Coast down – a condition whereby the rotation of a pump is decreasing from
full speed to rest speed when its driver de-energized. This is to be differentiated
from a free-wheeling condition. See free-wheeling.
Coke crusher -
Contact angle - When referring to ball bearings, the contact angle is the angle
between the line of action of the ball load and the plane perpendicular to the
Corebox - Pattern makers and foundry people make a distinction between the
outer portion and the inner portion of a casting. The pattern that defines the
outer or external portion of a casting is referred to as a pattern, and the pattern
that defines its inner portion is referred to as a corebox.
Corrosion allowance -
Cover - the part of the pump that is required to complete the case of a radial
Crevice corrosion -
Critical speed - the rotating speed at which resonance occurs with the natural
frequency of a rotor, or rotating assembly. The natural frequency of a rotor is
the frequency at which it will develop its highest vibration; it is affected by the
stiffness, or spring constant, and the weight, or mass, of the rotor. A pump
should not run at, or close to, its critical speed because it will result in excessive
and damaging vibration. See dry critical speed, and wet critical speed.
Crowning - see case crowning
Cutwater - an imaginary circle drawn from the shaft centerline and tangent to
the tip of the volute lip/s.
Cutwater diameter - the diameter of a cutwater, or the diameter of a circle
tangent to the volute lip/s and whose center is at the shaft centerline. The
cutwater diameter is used in calculating the pump's B-gap.
Cyclone separator -