MIL-PRF-19004B
duct if necessary to obtain fan-motor unit operation at the design point. The
fan-motor unit with attached discharge duct shall be placed within the
chamber. A section of the discharge duct, approximately 2 to 3 duct diameters
long and housing an orifice plate, shall extend into the reverberant test
room, and sound pressure level measurements shall be made within the reverb-
erant test room. Acoustical treatments shall be placed within the chamber as
necessary to provide an acoustic seal at the penetration in the wall
separating the chamber from the reverberant room, and to ensure that no noise
contributions are transmitted from the chamber into the reverberant test room.
4.7.5.4 Casing sound power. Test procedures and calculation procedures to
determine sound power levels radiated from the casing of a fan-motor unit
shall be in accordance with Appendix G of AMCA 300-96. Duct sections attached
to a fan-motor unit to facilitate testing to determine casing radiated sound
power shall be rigid, heavy gauge metal ducts and/or solid, double wall ducts
to eliminate noise contributions transmitted through duct walls. The noise
transmission loss of the walls of the reverberant test room shall be such that
noise transmitted into the reverberant test room from adjacent spaces does not
contribute to the sound power levels of the fan-motor unit. Penetrations in
the walls of the reverberant room in way of ducts shall be acoustically sealed
to prevent noise contributions from being transmitted into the reverberant
test room from the adjacent room.
4.7.5.5 Airborne noise detected by ear. Fan-motor units not undergoing
airborne noise testing described in 4.7.5.1 through 4.7.5.4 shall be operated
at their design points. Any unusual airborne noise or any airborne noise
thought to be excessive shall be corrected if the cause is apparent. If the
cause is not apparent and the condition is not corrected, the fan-motor unit
shall be tested in accordance with 4.7.5.1, and sound power levels shall be
computed to determine conformance with sound power level requirements
specified in Table IV.
4.7.5.6 Airborne noise test facility. The facility wherein measurements of
fan-motor unit airborne noise are performed shall be registered in accordance
with AMCA 111 as being a qualified facility in which to perform octave band
sound measurements in accordance with AMCA 300-96.
4.7.6 Motor temperature. Motor temperature rise shall be measured as
specified in the applicable motor specification. In each test, the motor
shall be installed on the fan, and a duct shall be attached to the discharge.
Maximum load shall be obtained by means of terminal throttle on the test duct.
Since neither the fan nor a test stand will normally be available at the motor
plant, the test may be conducted at the plant of the contractor. Motors with
a temperature rise of any part in excess of specification limits or bearings
in excess of 3.16.5 shall be rejected.
4.7.7 Explosion. This test is applicable only to electrical equipment
requiring an explosion-proof enclosure. Test shall be performed in a
petroleum ether atmosphere and certified by a nationally recognized
laboratory. Test shall include the conduit and conduit box actually used with
the fan. Prior to the explosion test, the air leakage rate of the motor
enclosure shall be determined by pressurizing2 the interior of the motor
enclosure to 10 pounds per square inch (lb/in ) and measuring the period of
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time in seconds for the pressure to drop from 10 to 4 lb/in . The air leakage
rate shall be recorded on the applicable motor drawing.
4.7.7.1 Air leakage rate. The motor of explosion-proof fan-motor units shall
have motor enclosure air leakage rate measured to determine whether the rate
of leakage exceeds that determined in 4.7.7. Any explosion-proof motor where
there is evidence that the predetermined rate of leakage is exceeded when
measured shall not be offered for delivery.
4.7.8 Casing tightness.
The casing tightness test shall be conducted as
follows:
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