MIL-DTL-151F
3.
REQUIREMENTS
3.1 Preproduction sample. Prior to production, a fan of each class and type offered for delivery, constructed
in accordance with an approved drawing (see 3.23), shall be examined, tested and approved as specified in 4.2.
3.2 Material. The material shall be of the best commercial quality and suitable in every respect for the purpose
intended. Cast iron shall not be used.
3.2.1 Class 1 magnetic fans. When class 1 fans are specified (see 6.2), the parts may be constructed of
paramagnetic materials satisfactory to the procuring activity concerned.
3.2.2 Class 2 nonmagnetic fans. When class 2 fans are specified (see 6.2), all parts except the magnetic circuit
shall be of nonmagnetic material. Nonmagnetic material is defined as material which has a maximum permeability of
less than 2.0 after fabrication.
3.3
Blades and guards.
3.3.1 Blades. Fans shall have not less than three blades of the diameter specified (see 3.18), which shall be
corrosion-resisting metal, polished and lacquered; or (for class 1 fans only) of a metal treated in a manner, satisfactory
to the procuring activity to resist corrosion and finished to match frame, base, and guard; or of a laminated plastic
approved by the procuring activity conforming to MIL-I-24768/1 or MIL-I-24768/17. Fan blades shall be of such design
that normal cleaning and dusting will not result in their being bent out of alignment. When mounted as shown on figure
1, the plane of rotation of the fan blades shall be parallel to the ceiling.
3.3.2 Guard. The guard shall be corrosion-resisting metal, polished and lacquered; or (for class 1 fans only) of a
metal treated in a manner satisfactory to the procuring activity to resist corrosion and finished to match frame, blades,
and base. It shall be sufficiently rugged to prevent distortion under normal operating conditions and shall adequately
protect personnel from injury. The guard shall be securely fastened to the motor frame by screws or other means to
permit ready removal and it shall not vibrate excessively when the fan is in operation.
3.4
Fan characteristics and mounting.
3.4.1 Characteristics. The characteristics of the fan shall be such that the air will be drawn from the area directly
below the blades and delivered in a plane parallel to the ceiling when mounted as shown on figure 1.
3.4.2 Mounting. Fans shall be designed for mounting in an overhead position, either directly or by means of an
auxiliary bracket, as shown on figure 1.
3.4.2.1
Mounting holes. The fan assembly shall have at least 4 mounting holes. The mounting shall be solid.
Grommets or isolation mounts shall not be used.
3.5
Motor.
3.5.1 Bearings. The bearings shall be self-lubricating, and shall be so designed as to prevent dripping and throwing
of the lubricating compound. Bearing may be ball or sleeve type.
3.5.2 Temperature rise. The temperature rise of the motor, when measured by a thermometer in contact with the
windings, shall not exceed 40º Centigrade (C), and when measured by a change in resistance shall not exceed 50º C.
3.5.3 A. c. motors. The design shall be such that no commutators, collector rings, or any automatic starting
devices shall be used.
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