a combination of cast steel and steel plate] [stainless steel plate].
[Steel plate, if used,][Stainless steel plate] shall have thickness of not
less than [_____] mm inch after machining is completed. Welds shall be
heat-treated stress-relieved before final machining. Provide flanges for
mating with [suction bell][formed suction intake] and impeller bowl or
two-piece construction of impeller. Flanged connections with suction bell
and the diffuser or split construction shall be provided with a rabbet fit
or four equally spaced dowels installed in the vertical position for
initial alignment purposes and to maintain concentric alignment of pump.
Machine finish impeller-swept area in impeller bowl to at least 3.2 m 125
microinch rms and concentric with impeller axis. For mixed-flow impellers,
angle in impeller bowl shall equal the outside angle of impeller blade
tips. Tolerance for concentricity of impeller with the impeller axis shall
not be greater than 20 percent of the operating clearance between impeller
and impeller bowl.
2.2.6
Diffuser Bowl
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NOTE: Use same thickness for the steel plate as
specified in paragraph IMPELLER BOWL.
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Make diffuser bowl of [cast iron, cast steel, welded steel plate, or a
combination of cast steel and steel plate][stainless steel plate]. [Steel
plate, if used,][Stainless steel plate] shall have thickness of not less
than [______] mm inch after machining is completed. Diffuser shall contain
support for upper impeller shaft bearing and have vanes to guide the pumped
flow. Equip diffuser bowl with a bypass drain to outside of pump from the
diffuser cavity located between the enclosing tube connection and impeller.
Furnish throttle bushing located in the cavity immediately above impeller.
Bypass drain and throttle bushing should be designed to reduce water
pressure on lower seal. Impeller back-wear rings can also be used to
reduce water pressure on lower seal.
2.2.7
Pump Column and Discharge Elbow
2.2.7.1
Column and Discharge Elbow
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NOTE: Use same thickness for the steel plate as
specified in paragraph IMPELLER BOWL, above. For
most pumps, space should be provided for using a
long radius type elbow. Unless the elbow is made of
cast materials, the elbow will be the mitered type.
The roundness tolerance should be specified when the
flexible coupling is not part of the contract.
Turning vanes shall be used in pumps having access
door to inspect/remove trash.
The following tolerance should be used for
specifying the tolerance for the plain end of the
elbow.
SECTION 15131A
Page 24
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