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|  MIL-P-18682D(SH)
3.2.7.1.4 Hydrodynamic radial bearings may be of the fixed or self-alining
type and shall operate under full-fluid film lubrication for all operating condi-
tions, except boundary lubrication will be permitted during pump start-up and
shut-down. Where the requirement for full-fluid film operation cannot be met, a
hydrostatic bearing may be recommended by the contractor for design review agency
approval. The hydrostatic bearing shall operate without metal-to-metal contact
over the entire range of the pump characteristic curve.
3.2.7.1.5 Water lubricated hydrodynamic radial bearings shall not be
provided with lubrication grooves unless specifically recommended by the
contractor and approved by the design review agency. If a hydrodynamic bearing
design having axial grooves is recommended by the contractor, positive proof of
the direction of radial loading shall be established. The orientation of the
bearing shall be such that the effective bearing arc will not be reduced to less
than 120 degrees at any operating condition of the pump. Orientation of the
bearing shall be maintained by positive means. The effective arc is defined
herein as the continuous load-carrying surface which is symmetrical with respect
to the load vector. Release for manufacture shall be subject to verification
of the applied load direction, by experimental data, and derived from tests of
manufacturer's own similar designs, Where the method or experimental data are
considered inconclusive by the design review agency, the recommendation for a
grooved bearing design will be disapproved.
3.2.7.1.6 The hydrodynamic and hydrostatic bearing surface and the journal
shall be finished to 32 roughness height rating (RHR) or better.
3.2.7.1.7 Type III pumps utilizing water-lubricated bearings shall use
one or more of the following means to minimize radial loading on the shaft:
(a)
Double volute casing.
(b)
Concentric casing.
(c)
Diffusers.
(d)
Modified concentric casing.
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 concentric casings, the ratio of the casing diameter at the cut water
to the impeller diameter shall be 1.3 or greater.
3.2.7.2 Thrust bearings.
3.2.7.2.1 A suitable thrust bearing shall be installed in each flexible
coupled unit for counteracting the forces resulting from the conditions stated
in 3.2.7.
3.2.7.2.1.1 Thrust bearings shall be of the combined radial and thrust
rolling contact type in accordance with 3.2.7.1.2.
3.2.7.2.2 For rigidly coupled units, the thrust bearing for the unit shall
be in the driver and shall comply with 3.2.7.2.1.1. For rigidly coupled units
where the driver is a turbine rated 500 horsepower (hp) or over, the thrust bear-
ing shall be as specified in MIL-T-17523.
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