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|  MIL-P-18472G(SH)
3.2.7.3 Water-lubricated
bearings. Water-lubricated bearings shall be
lubricated by the pumped fluid, and shall operate without metal-to-metal contact
at all pump operating conditions. Unless otherwise approved by the design review
agency, water-lubricated bearings shall be hydrodynamic and shall operate under
full-fluid film lubrication for all operating conditions, except boundary
lubrication will be permitted during pump start-up and shutdown. Where the
requirement for full-fluid film lubrication cannot be met, a hydrostatic bearing
may be recommended by the contractor for design review agency approval.
3.2.7.3.1 Construction . Water-lubricated bearings shall be of the fixed or
self-aligning, one-piece sleeve (bushing) type. Bearing bushing and journal
surfaces shall be finished to 32 roughness height rating (RHR) or better.
Bearings shall not have lubrication grooves, except a circumferential groove is
permitted if needed for lubricant feed.
3.2.7.3.2 Restrictions. Water-lubricated bearings shall not be used in
single stage pumps or in pumps with single volute casings.
3.2.7.3.3 Pump casings. Where water-lubricated bearings are used, the pump
casing shall be of the double volute type, diffuser type, concentric type or
modified concentric design to minimize radial bearing load.
For modified
concentric casings, the casing shall be circular over at least 270 degrees of
the arc beginning at the cut water and proceeding in the direction of impeller
rotation toward the discharge nozzle. For both concentric and modified concen-
tric casings, the ratio of the casing diameter at the cut water to the impeller
diameter shall be 1.3 or greater.
3.2.7.4 Thrust bearings.
A thrust bearing shall be installed in each unit
for counteracting the forces resulting from the conditions stated in 3.2.7. The
bearings shall be of the combined radial and thrust rolling contact type in
accordance with 3.2.7.2.
3.2.7.4.1 Rigidly coupled units. For rigidly coupled units, the thrust
bearing for the unit shall be in the driver and shall comply with 3.2.7.4.
3.2.7.4.2 Flexibly coupled units . For vertical flexibly-coupled pumps,
thrust bearings shall be installed at the top, external of the pump, between the
coupling and stuffing box. For rigidly coupled pumps, the thrust bearing shall
be located in the driver and shall conform to all the requirements stated herein.
3.2.8 Lubricants. The only permitted lubricants shall be water or the
pumped fluid, grease in accordance with DOD-G-24508, lubricating oil in accor-
dance with MIL-L-17331 (Military symbol 2190 TEP), graphite in isopropanol in
accordance with MIL-L-24131 (Military symbol CGI), and (for turbine drivers only)
as otherwise permitted by MIL-T-17523.
3.2.8.1
Thread lubricant . Thread lubricant for pump fasteners both inside
and outside the pumped fluid boundary shall be graphite in isopropanol in
accordance with MIL-L-24131 (Military symbol CGI). This lubricant, or water,
shall be used where an assembly lubricant is required for other pump internal
parts.
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