MIL-PRF-24755B(SH)
3. REQUIREMENTS
3.1 First article. When specified (see 6.2), a sample shall be subjected to first article inspection in accordance
with 4.2.
3.2 Materials. Fan shall be of spark-resistant construction as defined in AMCA 99-0401 Type B construction.
Cast iron, excluding nodular iron, shall not be used in the construction of fans or motors that are components of fans.
Materials shall be corrosion-resistant or material shall be protected against corrosion after fabrication. Material
degraded during the fabrication process shall be normalized to restore those properties before assembled in any fan.
Selected materials shall be capable of meeting all of the operational and environmental requirements specified
herein.
3.2.1 Composite material.
3.2.1.1 Composite fan casing. Fan casing shall withstand a full-scale fire performance test, as well as all
required tests of this document when used in a fan assembly. Acceptance criteria for composite casing material shall
be in accordance with the fire and toxicity performance requirements of MIL-STD-2031.
3.2.1.2 Fan internal components. Composite material used for motor, vanes, impeller, and conduit shall
withstand small-scale material specimen fire tests, as well as all required tests of this document when used in a fan
assembly.
3.2.2 Hazardous materials. Materials for use in the construction of fans shall have no effect on the health of
personnel when the materials are used for their intended purpose. Regardless of other requirements, materials and
parts containing asbestos, cadmium, lithium, mercury, or radioactive material shall not be used.
3.2.3 Fasteners. Material for all bolts, nuts, studs, screws, and similar fasteners shall be corrosion-resistant
passivated or of a material rendered resistant to corrosion. Sheet metal screws shall not be used. Galling shall be
prevented. Tapped holes shall be reinforced where shearing of thread can occur.
3.2.4 Nonmagnetic construction. When nonmagnetic fan-motor units are specified (see 6.2), all fan parts
including the casing, vanes, impeller, impeller bushing, motor mounting, fasteners, washers, conduit box, and
fittings shall be of nonmagnetic material (see 6.7.1).
3.2.5 Motor material. Motor material shall conform to the requirements of IEEE 45 or NEMA MG 1 as
applicable for nonmagnetic motors.
3.2.6 Dissimilar metals. Fans and components shall not be degraded by electrolysis (see 6.6).
3.2.7 Recovered materials. Unless otherwise specified herein, all equipment, material, and articles
incorporated in the products covered by this specification shall be new and may be fabricated using materials
produced from recovered materials to the maximum extent practicable without jeopardizing the intended use. The
term "recovered materials" means materials that have been collected or recovered from solid waste and reprocessed
to become a source of raw materials, as opposed to virgin raw materials. None of the above shall be interpreted to
mean that the use of used or rebuilt products is allowed under this specification unless otherwise expressly
stipulated.
3.3 Painting. Equipment and component items shall be delivered with the manufacturer's standard finish,
except as to comply with the requirements of 3.2.
3.4 Welding and allied processes. Surfaces of parts to be welded or brazed shall be free from rust, scale, paint,
grease, and other foreign matter. Welding and allied processes shall be performed by personnel certified to
American Welding Society standards ANSI/AWS B2.1/2.1M and ANSI/AWS B2.2. NAVSEA Technical
Publication S9074-AR-GIB-010/278 may be used for guidance.
3.5 Identification.
3.5.1 Fan identification code. The size and characteristics of Navy standard high pressure fan-motor units shall
be designated by a code formed by alternate letters and numbers arranged in accordance with table I.
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