Page 333 - Centrifugal Pumps 2E

298 Centrifugal Pumps: Design and Application

Support Head

The support head is the member that aligns and fixes the casing to the
bearing housing. ANSI requires the support head to be made of ductile
iron or carbon steel. This requirement stems from concern that a system
upset could subject the pump to excessive pressure and result in cata-
strophic failure of the cast iron support head. Support heads are also of-
fered in stainless steel as an optional feature. This is done for three rea-
sons:

• To reduce corrosion due to leakage from packing or mechanical seals.
« To reduce thermal conductivity in very high or very low temperature
applications.
• To have a material that has high impact properties for temperatures be-
low 40°F.

On vertical in-line pumps, the support heads are larger than horizontal
pumps because they must allow the rotor to be passed out of the support
head during disassembly and also must adequately support the weight of
the vertical motor. When a bearing housing vertical in-line is employed,
the support head is at least 50% higher in height than with the rigid cou-
pling design. Depending on size and motor horsepower, the support
heads are made out of cast iron, ductile iron, or fabricated steel. When
the vertical support heads are made out of ductile iron or carbon steel,
extra care has to be taken in machining the toleranced dimensions be-
cause of the release of residual stresses in these materials.

Bearing Housing

This is usually made out of cast iron. After machining, it is protected
internally with a rust preventative such as a paint or clear material to pre-
vent rust particles from forming internally in the housing during storage
or shut down. The housing is designed to hold a reservoir of oil that is
approximately a half pint on the small pumps, and 3 to 4V2 pints on the
large pumps. The housings have vents, drains, and a tap for an oiler. The
vent and drain should be a minimum of Va in. so the oil can readily flow
during filling or draining. The vent should be designed in a way that wa-
ter cannot enter into the housing. Sometimes the vent is made up of a pipe
that comes up through the bottom of the housing; other times it is com-
posed of a nipple and cap with a sixteen-hole or commercial vent. The
oiler is located so mat movement of the oil from the rotation of the shaft
does not prevent the oil from entering into the housing. Oilers are sup-