2.2.8.1
Removal and Prior To Finishing
After removal from mold, and prior to finishing of surface imperfections,
castings shall be inspected by Contracting Officer. Minor surface
imperfections shall be filled or ground down as necessary to preserve
correct contour and outline of impeller and to restore surface
imperfections to the same degree of finish as surrounding surfaces.
Correct surface pits, depressions, projections, or overlaps showing greater
than 2 mm 1/16 inch variation from the general contour for that section.
Method and procedure for accomplishing repair shall be as required in
Section 05055A METALWORK FABRICATION, MACHINE WORK, MISCELLANEOUS
PROVISIONS. Castings that exhibit surface imperfections (as defined above)
covering an area of more than 10 percent of blade surface will be rejected.
2.2.8.2
Balance
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NOTE: The maximum operating speed is used for
driver/pumps which operate at different speeds. The
rated operating speed is used with a single speed
driver. The g-mm (oz-in.) used in this paragraph
are determined from Figure 2.1 of ANSI S2.19 for
grade G6.3. Impellers for pumps having a discharge
diameter greater than 600 mm (24 in) shall have the
impeller weighted. The amount of allowable
unbalance or the level of balance in the acceptable
standards must be chosen and included in this guide
specification. This includes choosing acceptable
standard(s). A suggested standard is balance
quality grade G6.3 in accordance with ANSI S2.19.
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Balance impeller by the two-plane balancing technique. Impeller shall be
balanced at [maximum] [rated] operating speed. Check balance at 110
percent of balance speed, and make needed corrections. Amount of allowable
unbalance shall be in accordance with grade G6.3 of ANSI S2.19. Weights
needed to obtain required level of balance shall be securely fastened to
inside cavity of impeller hub. In no case will portions of the impeller be
removed or weights be added to outside of hub, vanes, or water passages.
Submit balancing procedure to Contracting Officer for approval at least
four weeks prior to date of balancing. Each finished impeller shall be
weighted and weight stamped on the bottom of hub. Weight shall be accurate
to 0.5 percent of the total weight of impeller. Weighing and balancing
shall be witnessed by Contracting Officer.
2.2.9
Shafting
2.2.9.1
Shaft
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NOTE: Stainless steel shafting should be used when
the potential for corrosion is high such as a pump
used in a station where the pump/station sump is not
capable of being unwatered. The shaft lengths are
limited in length by the headroom available. Shaft
sections are usually less than 3000 mm (10 ft) in
length. Vertical adjustment of the shaft should be
performed above the operating floor. The motor and
gear reducer are normally specified to be hollow
SECTION 15131A
Page 31
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