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Page Title:
Casing design (submarine sea water pumps only) |
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|  MIL-P-18682D(SH)
At 140 percent
At rated flow
rated flow
At shutoff
Casing type
0.00024Ns for Ns
Single volute
0.10
0.36
less than 1500
0.36 for Ns of
1500 or greater }
.10
0.11
.05
Double volute
Concentric and
.15
.15
.15
modified concentric
.15
.15
.07
Vaned diffuser in volute
.15
.07
.03
Vaned diffuser in concentric
Where:
Ns = specific speed at the best efficiency point.
(2) Effects of thrust reversal where conditions which
might cause thrust reversal exist.
(3) Effects of roll, pitch, list and trim of the ship
(including gyroscopic effects) shall be considered
in the bearing design.
(4) Bearing clearance ratios, L/D ratio and characteristic
numbers, lubricant flow, and temperature rise (water-
lubricated bearings).
(5) Minimum film thickness required and calculated under
maximum radial and axial load conditions over the
range of specified pump operating conditions (water-
lubricated bearings).
(c) Analysis of driver bearings for close-coupled or rigidly coupled
units.
(d) Calculations of the worst case cumulative effect of dimensions
and tolerances for parts and locations. These calculations shall
demonstrate:
(1) There will no interferences between rotating and
stationary parts as-assembled.
(2) There will be no interference between rotating and
stationary parts and hence no reduction in life of
wearing parts, when these worst case cumulative
effects are combined with operational, environmental,
and thermal loading.
(e) Casing design (submarine sea water pumps only). In the design
of submergence pressure boundaries in sea connected pumps for
submarine application, full consideration shall be given to
the cyclic nature of the submergence pressure, external nozzle
loading, and liquid temperature. The design of the pressure
containing parts shall be in accordance with the following basis:
(1) Attached system piping size and material shall be as
specified (see 6.2.1).
(2) Pressure and temperature transients as specified (see
6.2.1).
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