FED-STD-791D
settings of the manometer and rotameter are observed and recorded for a wet-test gas meter
reading of 9.91 L/sec (0.35 cfm). The air line is then reconnected to the bearing head and the
previously observed manometer and rotameter settings are maintained throughout the test.
4.2.5.2 Screw seal. The screw type seal is vented to atmosphere at both the top and
bottom seal housing connections.
4.2.5.3 Connection for seal differential pressure measurement. The lines of the
manometer used to measure the differential pressure across the seal should be connected to the
top, front of the bearing head, and to the rear vertical surface of the bearing housing between 11
and 1 o'clock, 2.54 cm (1 in) above the junction of the rear case with the main housing. After
startup, there should be no venting of the manometer lines. In this connection, the pipe plug in
the top of the gearbox should be removed and replaced with a small valve to allow adjustment of
the pressure in the gearbox and, hence, in the support system. The adjustment of the pressure of
the atmosphere of the support-oil system controls the pressure drop across the screw seal, which
is used to insure against oil transfer from the support section to the test-oil section. The required
differential is controlled by maintaining a slightly higher test-oil compartment pressure of 0.76 to
1.27 cm (0.3 to 0.5 in) of test-oil column relative to the support-oil compartment pressure.
4.2.5.4 Sump air venting. The sump is vented to the atmosphere through a sump cover
port as shown on Figure 2. A line connected to the port terminates at a valve which permits
connection of the line to a gas-flow meter. When the required test conditions are attained after
each startup, the flow rate of the gas discharging from the sump is measured at the valve
employing a portable gas flow rate meter. The speed control of the scavenge pump motor is set
to provide a sump gas discharge of 14.16 L/sec (0.5 cfm). During a test, additional
measurements of the sump vent gas flow rate should be made when excessive scavenge pump
wear or test-oil system air leaks are suspected.
4.2.5.4.1 The procedure for the sump-air venting discussed above is modified for bearing
tests employing sump bulk-oil temperature above 176.7C (350F). The valve is closed to the
atmosphere and vent pipe-blower assembly is connected to the sump oil-fill port, as shown on
Figure 4 to condense the increased oil vapor created in the sump by the elevated oil temperature.
Oil vapor/mist condenses in the blower housing and is drained back into the sump. The
measurement of the sump vent gas flow rate is made at the valve as previously discussed.
However, the vent pipe-blower assembly is removed and the sump-oil port is capped each time
the airflow rate is to be measured. After each measurement, the vent pipe blower assembly is
replaced at the sump-oil fill port.
5. MATERIALS
5.1 CAUTION: SOME MATERIALS ARE TOXIC AND HAZARDOUS. The
materials references and standards listed in this section must be handled carefully. Federal Test
Method 10000, Material Handling Safety Precautions, is a reference which lists all toxic and
hazardous materials cited in FTMS 791. The synonyms, life hazard, flammability, handling and
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