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Calculations shall be submitted to cover the following |
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|  MIL-P-17881D(SHIPS)
(c) Type of coupling including previous service experience.
(d) Those areas in which system design conditions, as furnished by the pro-
curing activity, adversely affect pump reliability or result in abnormal
design features.
(e) Steps required for disassembly and reassembly (including alignment) to
perform routine maintenance.
(f) Any other design features which the manufacturer considers of significant
interest to describe the proposed unit.
3.11.3 Use of materials other than as specified herein shall be justified. It is not
intended that materials which conform to and are used as specified herein shall require
justification.
#
3.11.4 Calculations shall be submitted to cover the following:
(a) Shafting analysis of pump and driver assembly including calculation of
critical speed. If calculations are done by computer, the method of analysis
shall be described and only the results shall be submitted with identifica-
tion of corresponding pump parameters used in the calculations. The following
shall form the basis of the critical speed calculation:
(1) The effects of all major changes in shaft cross section moment of
inertia shall be included.
(2) NO support for the shaft shall be assumed other than at the designated
bearings.
(3) All masses in the rotating system, including the effect of entrained
fluids, shall be lumped at discrete points along the shaft. .
(4) No support for any shafting shall be assumed to be provided by
additional shafting when two sections of shafting are separated by a
flexible coupling, nor should any flexibility in bending or shear be
assumed for a rigid coupling.
(5) For pumps which operate under variable speed conditions, the operating
speed shall be construed to be the maximum operating speed.
(b) Loads imposed on the shaft and bearings. The calculations shall include the
following:
(1) Axial and radial loads and load directions. Loading should be cal-
culated for the design point and also for the highest loaded conditions
over the operating range. These loads shall include all operating
loads together with those that might be induced by thermal expansion,
by bearing preload and by build-up of tolerances in the completed
assembly. The radial loads at the impeller shall be calculated by the
following:
Where:
P = the radial load in pounds.
H = head in feet.
= impeller outside diameter, inches.
= impeller overall width including shroud, inches.
K = a constant which varies with capacity.
Unless data, supported by tests, justifies the selection of a lower
value, K shall be in accordance with the following. Lower K values
may be used only if specifically approved by the design review agency.
At 140 percent
At rated flow
rated flow
Casing type
At shut off
0.00024Ns
Single volute
for Ns less
than 1500
0.10
0.45
0.36 for Ns
of 1500 or
greater
0.10
0.05
Double volute
0.07
0.50
0.36
Concentric
0.15
0.15
0.15
Modified concentric
0.07
Vaned diffuser in volute
0.15
0.15
Vaned diffuser in
0.03
0.07
0.15
concentric
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