MIL-PRF-24751A(SH)
3.15.3 Airborne noise. The total sound power levels for the fan-motor unit shall not exceed the levels stated in
Tables II and III when measured in accordance with procedures stated in 4.5.3. Exceeding the total sound power
levels specified in Table III shall be cause for rejection.
3.15.4 Atmospheric spray. Able to operate satisfactorily when exposed to soaking atmospheric spray (rain or
sea) or seawater.
3.15.5 Ambient temperature. Perform in accordance with requirements herein in a range of ambient
temperatures between minus 29 and 65 °C.
TABLE II. Airborne noise acceptance levels.
Sound power level in decibels (dB) with reference to 10-12watt
Fan
Freq.
Model
Hz
311/
63
125
250
500
1K
2K
4k
8K
12½ hp
99
95
94
90
93
104
102
98
91
25 hp
104
100
99
95
98
109
107
103
96
80 hp
110
106
105
101
104
115
113
109
102
130 hp
112
108
107
103
106
117
115
111
104
Note:
1/
Data at 31 Hz reported for information only.
TABLE III. Casing transmission noise acceptance levels.
Sound power level in decibels (dB) with reference to 10-12watt
Fan
Freq.
Model
Hz
311/
63
125
250
500
1K
2K
4k
8K
12½ hp
62
65
72
64
63
82
72
71
61
25 hp
67
70
77
69
68
87
77
76
66
80 hp
73
76
83
75
74
93
83
82
72
130 hp
75
78
85
77
76
95
85
74
74
Note:
1/
Data at 31 Hz reported for information only.
4. VERIFICATION
4.1 Classification of inspections. The inspection requirements specified herein are classified as follows:
a.
First article inspection (see 4.2).
b.
Conformance inspection (see 4.3).
4.2 First article inspection. First article inspection shall be performed on type TA vaneaxial fans when a first
article sample is required (see 3.1). This inspection shall include the examination of Table II.
4.3 Conformance inspection. Conformance inspection shall consist of the examinations of 4.6 and tests as
specified in Table IV. The tests specified shall be performed on each size fan-motor unit. Any unit that fails to meet
any specified requirements shall be rejected.
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