FED-STD-791D
4.3.1.1 Bearing assemblies. Four front outer bearing assemblies, and four front inner
bearing assemblies, with bearing races and grease seals.
4.3.1.2 Hub and brake drum assemblies. Four left front wheel hub and brake drum
assemblies.
4.3.1.3 Helper springs. One helper spring per wheel assembly.
4.3.2 Brake pressure actuating mechanism. A suitable actuating mechanism for applying
pressure to the master cylinder push rod to simulate, as closely as possible, the braking operation
in a vehicle.
4.3.2.1 Type of actuating mechanism. The actuating mechanism shall be operated by
suitable air pressure or hydraulic means. Mechanical actuation is not recommended.
4.3.2.2 Pressure application. The amount of pressure applied by the actuating
mechanism shall be adjustable. The mechanism shall be capable of applying sufficient thrust to
the master cylinder to create a minimum pressure of 6.9 gage MPa (1000 psig) in the simulated
brake system.
4.3.3 Stroking rate and rate-of-load application. The actuating mechanism shall be
designed to permit adjustable stroking rates ranging from 500 to 1,000 strokes per hour as
desired. The ratio of percent time-of-load application to non-load application shall also be
adjustable, from a minimum ratio 25/75 percent to a maximum of 60/40 percent per stroke cycle.
(A "60/40 percent" ratio per stroke cycle indicates that pressure is applied during 60% of the
duration of the stroke cycle, while the pressure is released, or not applied, during the remaining
40% of the cycle.)
4.3.4 Pressure gages. Two recording pressure gages of 0 to 6.9 gage MPa (0 to 1000
psig) capacity with connecting tubing. One of the gages shall have a 24-hour cycle, while the
other gage shall have a maximum cycle of 6 min. Each gage shall be provided with a shut off
valve for removing air from the connecting tubing.
4.3.5 Revolution counter. A mechanical or electrical revolution counter with recording
capacity for 500,000 strokes.
4.3.6 Tubing. Approximately 4.6 m (15 ft) of 0.63 cm (1/4 in) O.D. copper or steel
tubing with inverted flare nuts, connectors, adaptors, and fittings.
4.3.7 Stand. A stand or frame for mounting the four left front wheel assemblies as
shown in Figure 1.
4.3.8 Cabinet or oven. A large cabinet or oven, of sufficient capacity to house the stand
with
the four mounted wheel assemblies, together with the master cylinder and necessary
connections.
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