FED-STD-791D
the master cylinder shall be stroked several times to completely fill the system. All the wheel
cylinders and the tubing connected to the pressure gages shall be bled to remove the entrapped
air from the system.
6.3.4 Checking the system for leaks. After the system has been bled, a pressure of 6.9
gage MPa (1,000 psig) shall be applied to the system. The system shall be slowly stroked for 10
min, after which an inspection shall be made for leaks. The pressure shall be released, and the
brake shoe clearance rechecked (6.3.2).
6.3.5 Fluid level. A constant level of test fluid shall be maintained at the master cylinder
throughout the test. Accurate record shall be kept of the number of mL of the fluid added to the
system during the test. It may be necessary to install special antisplash plugs on the master
cylinder reservoir to avoid loss of the fluid due to splashing.
6.4 Test procedure.
6.4.1 Procedure A. Stroking properties at high temperatures.
6.4.1.1 Conditions of test.
6.4.1.1.1 Test temperature. Unless otherwise specified the test temperature shall be 120
" 3C (248 " 5F). The test shall be started at room temperature (23 " 5C). The rise in
temperature from room temperature to the test temperature shall take place in not more than 8 h
from the start of the test.
6.4.1.1.2 Pressure. The initial stroking pressure in the simulated brake system shall be
adjusted at room temperature (23 " 5C), to 3.4 gage MPa (500 psig) and recorded. The
pressure stroke pattern shall be adjusted at 60/40 percent stroke ratio 17 strokes/min, with the aid
of the short-cycle pressure recorder, so as to produce a relatively smooth curve (see Figure 2).
Accurate record shall be kept of any pressure variations during the test. The pressure stroke
pattern shall be compared with the initial pattern at intervals of 50,000 strokes during the test.
6.4.1.2 Brake-in or burnishing run. The stroking rate shall be adjusted at 1,000 " 50
strokes per hour, using the 60/40 percent stroke ratio and the stroking pressure of 3.4 MPa gage
(500 psig) applied at room temperature (23 " 5C). While at room temperature, the system
shall be stroked 16,000 " 500 strokes. At the end of this stroking period the system shall be
checked for fluid level. The cylinder shall be filled to the given level, if necessary, and the test
resumed.
6.4.1.3 Duration of test. The test shall be run until 94,000 strokes have been completed.
The number of strokes given in the burnishing run (see 6.4.1.2) and in coming to test temperature
(see 6.4.1.1.1) shall be included as part of total 94,000 strokes. The number of strokes required,
if other then 94,000 shall be specified in the material specification.
6.4.2 Procedure B. Stroking properties at sub-zero temperatures.
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