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Calculations shall be submitted to cover the following |
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|  MIL-P-17639F(SH)
3.8.4 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 a computer, the method of analysis shall be described
and only the results shall be submitted with identification
of corresponding pump parameters used in the calculations.
The following shall form the basis of the critical speed
calculation:
The effects of all major changes in shaft cross section
(1)
moment of inertia shall be included.
No support for the shaft shall be assumed other than at the
(2)
l
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.
For pumps which operate under variable speed conditions,
(5)
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 shall
be calculated for the design point and also for the
highest loaded conditions over the operating range (see
6.2.1). 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 toler-
ances in the completed assembly and by ship roll, pitch,
list, and trim. 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.
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