MIL-PRF-18953C(SH)
4.6 Routine tests. Routine tests are required for every fan-motor unit. These tests are specified n Table III.
Any unit which fails to meet any specified requirements shall be rejected.
4.7 Material inspection.
4.7.1 Cast impeller and casing. Test samples shall be inspected for chemical content and mechanical properties
in accordance with ASTM B26 except radiography of visually sound castings is not required. Repairs of cast impeller
are not permitted. Cast casings may be repaired by welding or impregnation if completed in accordance with the
procedures specified in NAVSEA Technical Publication S9074-AR-GIB-010/278.
4.7.2 Fabricated steel casing. Visual examination for defects is required. Cracks in the radius of spun flanges or
in the welds of welded flanges may be repaired by welding, after proper preparation, provided that radiographic
inspection of the repaired area is performed. Wall thickness shall be measured on at least 10 percent of the casing.
4.8.1 High-impact shock. The fan-motor unit shall be shock tested on the medium weight machines as specified
for Grade A shock of MIL-S-901 if its weight, fixture and mounting bracket exceeds 550 pounds or if the mounting
bracket extends beyond the anvil; otherwise, it shall be shock tested on the light weight machine as specified for Grade
A shock of MIL-S-901; the motor shall be shock tested in accordance with the motor specification. The high impact
shock test shall be conducted as specified in 4.10. Evidence of fragmentation or missile effect of parts, deformation
that will cause active interference between parts, or failure to operate shall be cause for rejection. In this test, bolts
shall be used in each of the flange bolt holes. Resilient mountings shall not be used unless specified (6.2). If resilient
mountings (vibration or shock) are specified for use, classification of shock testing shall be determined in accordance
with MIL-S-901 criteria and the appropriate medium weight or lightweight shock test will be determined and
conducted. Fan-motor units that have passed this test may be used as production units after replacement of motor
bearings.
4.8.1.1 Shock on lightweight machines. The fan discharge (motor end) flange of Type A fan-motor units shall be
bolted to platform number 3, fixture 4 C and that of Type L fan-motor units to fixture 4 A, without bolt spacers or with
a single annular spacer as described in MIL-S-901. The test shall consist of nine blows with the unit operating at
maximum speed and nine blows with the unit not energized.
4.8.1.2 Shock on medium weight machines. The test of a fan-motor unit shall consist of the nine blows indicated
1.
Fan horizontal (motor shaft horizontal), steel mounting brackets attached to both fan flanges for
mounting to test platform.
2A. Fan vertical, fan impeller down (motor shaft vertical, impeller on bottom). Fan flange bolted to a steel
plate for mounting to test platform.
2B. Fan inclined at 30 degrees fan impeller up (motor shaft inclined 30 degrees from the vertical, impeller
on top). Fan flange bolted to a steel plate for mounting to test platform.
Auxiliary channels shall be used as necessary to bolt the mounting brackets or plate to standard fixtures.
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