MIL-PRF-18953C(SH)
TABLE I. Total sound power level in decibels (dB), referenced to 10-12 watt.
Octave band center frequency - Hz
Fan
Fan
type
size
63
125
250
500
1000
2000
4000
8000
A and
¼
81
79
80
80
80
76
73
67
X-A
½
81
81
81
82
82
80
77
71
1
83
82
84
84
84
82
79
73
1½
82
83
87
87
89
86
82
76
2
87
89
86
91
95
89
85
79
2½
85
91
90
91
91
88
85
80
3
86
88
92
94
92
90
83
77
3½
87
89
93
94
95
90
87
80
4½
92
91
96
100
98
96
93
87
5
87
89
93
93
93
89
83
82
6
92
91
94
95
94
91
86
82
7
94
94
100
100
100
98
94
88
8
93
96
93
95
95
92
87
82
10
92
97
98
101
96
93
88
82
11
94
101
102
102
100
97
91
89
12
94
97
96
99
98
95
90
86
16
95
97
97
100
101
97
94
87
17
97
99
103
107
107
101
94
90
20
96
98
102
102
102
100
97
91
25
95
97
101
101
99
95
91
87
28
99
98
99
105
103
101
96
91
30
96
98
102
102
102
97
93
88
L and
½
86
82
78
83
85
83
75
70
X-L
1
85
81
80
85
87
85
77
72
2
87
83
82
87
89
87
79
74
3
90
86
85
90
92
90
82
77
NOTE: Add 4 dB to the octave band in which blade frequency occurs.
3.10.2 Configuration. Fans and motors shall operate in any position on shipboard including vertical (with fan
impeller either up or down), horizontal (parallel to ship's centerline or athwartship), or inclined. Each fan-motor
unit shall be a complete assembly.
3.10.3 Fan impellers. The fan impeller shall require no assembly or disassembly except to be removable as a
unit from the drive shaft. Impellers shall be of airfoil design. The total impeller shall have at least a safety factor of
8, based on the ultimate tensile strength of the material. Impellers shall be designed to prevent retention of water
when the fan is installed vertically with the impeller up or down, or horizontally. The hub of the impeller shall not
distort or the fit loosen on the drive shaft during the life of the equipment.
3.10.3.1 Nose piece. If a nosepiece is required, it shall be match marked with the impeller or attached to it to
ensure reinstallation in the same position relative to the impeller.
8
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