![img](MIL-PRF-2475100006im.jpg)
MIL-PRF-24751A(SH)
3.7 Operating life. The equipment shall have an operating life of not less than 223,800 hours (equivalent to
approximately 30 years of operation). Any part identified as planned replacement parts shall have an operating life,
prior to replacement, of approximately 37,300 hours (equivalent to approximately 5 years of ship operation).
3.8 Human engineering. The fan shall be arranged so as to achieve safe, reliable, and effective performance by
the operator and maintenance personnel and to optimize personnel skill requirements. ASTM F1166 shall be
utilized as a guideline in applying human engineering design criteria for the fan-motor unit.
3.9 Maintainability. The fan shall be constructed so that:
a.
Fan impeller shall be mounted on the motor shaft in such a manner that it is removable using
commonly available tools.
b.
Bearings shall be removable using commonly available tools.
c.
Parts shall be match marked or attached so that reinstallation will be in the same position as originally
installed.
d.
Motor shall be removable using commonly available tools.
3.10 General shipboard design conditions. General shipboard design characteristics shall be as follows:
a.
Power source quality - In accordance with MIL-STD-1399-300.
3.11 Fan design requirements.
3.11.1 Aerodynamic design parameters. The quantities of blades and vanes shall be chosen to avoid interacting
frequencies within the audible range. The axial distance between blades and vanes shall be chosen with minimum
noise amplitude as a prime consideration. Blade tip clearance (radial clearance) shall be the minimum clearance to
satisfy 4.5.10.
3.11.2 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.
3.11.3 Sizes. Sizes of gas turbine cooling fans shall be limited to those listed in Table I.
TABLE I. Fan characteristics.
Max inside
Design
Max
Max
Max
flange
Length
Fan Size
Tp in W.G.1/
Volume
Horsepower
Weight
dim.
(inches)
ft3
(minimum)
(inches)
TA4½
4500
18
19
34
25
645
TA5
5000
10
19
24½
12½
331
TA17
17000
20
32
40
80
1390
TA22½
21200
22
32
40
130
1500
1/
Total pressure (Tp) in inches watergage.
3.12 Fan casings and associated parts.
3.12.1 Watertightness. Casings shall be watertight.
3.12.2 Flanges. Flanges for duct connections shall be provided at each end of the fan casing. These flanges
shall be integral parts of the casing either through manufacture or welding. The flanges shall have boltholes drilled
approximately 3 inches center to center.
3.12.3 Direction vanes. Airfoil shaped directional vanes shall be provided in the casing.
3.12.4 Motor mounting.
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