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|  MIL-T-l7491H (SA)
lowered and raised in the bottom boards opening with a minimum clearance of 1/4
inch (6 mm). The mechanism shall be recessed or otherwise protected to prevent
damage from impact and abrasion during normal operation. Linkages and wheel
supports shall move freely without dragging on pallet boards during raising and
lowering operations. The mechanism shall be capable of returning unloaded rear
wheels into the recessed position.
3.5.4 Wheels and rollers. When specified,the wheel and roller material shall
be of the conductive nonsparking type of impregnated synthetic mangenese,
bronze or brass for use in hazardous locations.
3.5.4.1 Front wheels. Unless otherwise specified (see 6.2), each truck shall
be equipped with dual front wheels, flat faced type. Wheels shall have
cured-on polyurethane tires and ball or roller bearings. Wheel castings snail
be of impregnated synthetic manganese, bronze, brass, steel,malleable or cast
iron or aluminum and shall be equipped with permanent, lifetime grease-sealed
bearings or accessible pressure lubrication fittings. Bearings shall have
seals or shields to retain grease, and exclude dust and moisture. TApered
roller bearings, when used, shall provide means for adjustment to compensate
for wear. Each wheel of dual front wheels shall be 8 inches (203 m) in
diameter minimum by 2 1/2 inches (64 mm) wide minimum.
3.5.4.2 Rear wheels. Unless otherwise specified (see 6.2), rear wheels shall
be of impregnated synthetic manganese, bronze, brass, steel, mallable or cast
iron or aluminum with cured-on polyurethane tires. Rear wheels shall be
concentric within l 020 total indicated reading. Wheels shall be equipped with
ball or roller bearings. Wheels shall be provided with permanent lifetime
grease-sealed bearings or accessible pressure lubrication fittings. Bearings
shall have seals or shields to retain grease and exclude dust and moisture.
Rear wheels may be tandem mounted. Each wheel shall be 3 inches (76 mm) in
diameter minimum by 3-3/4 inches (95 mm) in width minimum.
3.5.4.3 Entry and withdrawal devices. Pallet entry and withdrawal devices
shall be provided and shall be in accordance with the supplier's standard
practice except as specified herein. The entry and withdraeal devices shall
have a minimum underclearance of 1/8 inch (3 mm).
3.5.5 Steering. The trucks shall be steered through the dual front wheels by
a steering handle. The steering handle shall be fabricated from steel and
shall turn the steering assembly a minimum of 90 degrees to the left and 90
degrees to the right of dead center position. The steering assembly shall be
mounted on angular contact ball or tapered roller bearings or bushings.The
steering assembly shall have permanent lifetime grease-sealed bearings, or
provision for lubrication by accessible pressure fittings. Bearings shall have
seals or shields to retain grease and exclude dust and moisture. TApered
roller bearings shall provide means of adjustment to compensate for wear. The
steering handle shall be removable from the steering mechanism, using common
tools. The steering handle shall not exceed a height of 50 inches (1270 mm)
when measured vertically from floor level.
3.5.6 Hydraulic system. The hydraulic system of the trucks, including the
pump, ram, and reservoir shall be the sealed type unit(s). All sealed type
unit(s) shall be demountable and shall automatically hold a rated load in any
position upon release of the pump actuator without exceeding a downward drift
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