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|  MIL-P-17881D(SHIPS)
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3.3.8.2.2 Thrust bearings may be of the combined radial and thrust rolling contact
type (see 3.3.9) or pivoted segmental type.
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3.3.8.2.3 When pivoted segmental type thrust bearings are used, the design shall be
such as to permit renewal or refitting of shoes without removal of shafts.
3.3.8.2.4 When a rolling contact thrust bearing is used, the design shall be such as
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to permit replacement of the bearing without removing the pump rotor from the casing.
3.3.8.2.5 For vertical flexible coupled pumps, thrust bearings shall be installed at
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the top, external of the pump, between the coupling and the stuffing box. For rigidly
coupled pumps, the thrust bearing shall be located in the driver.
.
3.3.9 Rolling contact bearings.
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3.3.9.1 Except as otherwise approved by the design review agency, rolling contact
bearings shall be of the ball type in accordance with FF-B-171. Roller bearings may be
recommended if use of ball bearings is impractical. If approved, roller bearings shall be
in accordance with FF-B-185 or FF-B-187. Rolling contact bearings shall be selected to
result in a minimum B-10 life of 10,000 hours calculated in accordance with FF-B-171,
FF-B-185 or FF-B-187.
3.3.9.2 Rolling contact bearings specifically selected for quiet operation in accord-
ance with MIL-B-17931 shall be used for pumps for submarine applications and for surface
ships where required to meet special noise requirements.
3.3.9.3 Rolling contact bearings having a DN value in excess of 200,000 shall be oil
Lubricated, unless the vendor can demonstrate to the satisfaction of the design review
agency that the specific grease lubricated bearing application has been proven in previous
Navy shipboard service. Rolling contact bearings having a ON value in excess of 270,000,
shall not be used unless specifically approved by the design review agency.
Where D - Diameter of bearing bore in millimeters
N = RPM
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3.3.9.4 Rolling contact bearing lubrication method shall prevent bearing failure re-
sulting from overgreasing. Rolling contact bearing temperature shall not exceed
(as measured on the bearing outer race) with specified normal pumped fluid temperature and
specified maximum ambient air temperature outside the pump envelope. Straight holes with
plugs shall be provided in the bearing housing to permit insertion of a thermocouple probe
to contact the outer race diameter of each rolling contact bearing. Unless otherwise
specified (see 6.1), externally supplied cooling liquid or externally induced forced draft
shall not be required for satisfactory bearing temperature.
3.3.10 Couplings.
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3.3.10.1 Boiler feed pumps shall be of 4-bearing construction with a flexible coupling
between pump and driving unit. The use of other than 4-bearing construction required design
approval and will be considered only when the vendor can substantiate that satisfactory
alignment and bearing loads will be maintained. Rigidly coupled units may be used when
specified (see 6.1).
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3.3.10.2 Each flexible coupled unit shall have an all metal spacer type flexible
coupling as specified (see 6.1) connecting the pump rotor to the driving rotor. Drawings
shall indicate by note the maximum allowable backlash before replacement of the coupling
is necessary.
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3.3.10.3 All flexible coupling hubs shall be keyed to the shafts and secured by lock
nuts.
The hubs shall be fitted on a taper with keys.
3.3.10.4 All rigid couplings shall have fitted bolts and the coupling flanges shall
be marked at assembly to insure proper reassembly after overhaul of the unit.
3.3.10.5 Coupling guards shall be provided for each horizontal flexible or rigid
coupled unit. Guards shall be designed to permit ready access to the coupling for lubri-
cation, examination and maintenance.
3.3.11 Mounting bedplates.
3.3.11.1 Each horizontal pump and its driving unit complete with all appurtenances
shall be mounted on a common bedplate.
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