Graham Corporation
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1.2 General Description and Principle of Operation
Graham Vacuum Pumps and Compressors are of the liquid ring type. Single and two stage
pumps are available in a wide range of sizes and materials. These options are listed in the
Graham Sales Bulletins. The major component of the Graham pump is a multi-bladed rotating
assembly positioned eccentrically in a cylindrical casing. (See Figure 1) This assembly is
driven by an external source, normally an electric motor. Service liquid (usually water) is
introduced into the pump. As the impeller rotates, centrifugal force creates a liquid ring which
is concentric to the casing. At the inlet, the area between the impeller blades (buckets) increase
in size, drawing gas in. As the impeller continues to rotate toward the discharge, the impeller
bucket area decreases in size, compressing the gas. This gas, along with the liquid from the
pump, is discharged through the outlet nozzle. The service liquid is separated from the gas and
cooled for reuse in the pump or sent to a drain. In addition to being the compressing medium,
the liquid ring performs two other important functions:
1) It absorbs the heat generated by compression, friction, and condensation of
the incoming vapor.
2) It absorbs and washes out any process contaminants entrained in the gas.
A continuous supply of service liquid is necessary to limit the temperature rise in the pump
caused by the heat of compression, friction, and condensation. Any excessive rise in
temperature will have a detrimental effect on performance, reducing the capacity and degree of
vacuum attainable. Installation schematics for the supply of the service liquid and for the
separation of the gas and liquid discharged from the pump are shown in Section 2.
Gas
Inlet
Gas and
Li
uid Outlet
Shaft
Suction Port
Impeller
Gas
Dischar
e Port
Li
uid Rin
Rotation
Figure 1
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