7.2 Testing
7.2.1 Increase the test air pressure slowly.
7.2.2 Increase the air pressure until the valve start-to-discharge (STD) pressure is reached. The initial
opening of the valve may be slightly high and not indicative of the actual STD because the O-ring
may have been partially stuck to the valve seat. See Table 7-1 for valve start-to-discharge (STD)
and vapor-tight pressure (VTP) settings.
Table 7-1 Start-To-Discharge (STD) and Vapor-Tight Pressure (VTP) Settings
7.2.3 Reduce the air pressure until leakage stops and then reduce pressure to less than one-half of the
STD pressure. Then slowly increase the pressure.
7.2.4 Observe the STD pressure and then bleed off the pressure slowly to observe the VTP.
7.2.5 Repeat this procedure at least two (2) more times. The STD and VTP should be consistent in all
three (3) occurrences.
7.2.6 AAR Specifications state that the VTP is 80% of the STD. Valves with good seats and O-rings
should exhibit a VTP above 80% of the STD (usually up to 95% of the STD).
7.2.7 Retest the valve.
7.2.8 If the test results are erratic, troubleshooting is more complex. Consult your supervising engineer
or a Midland representative.
7.2.9 When the test results are acceptable, tighten the bottom locknut to torque specifications as
indicated in Table 1-2.
7.2.10 If the STD or VTP is not satisfactory, take the O-ring retainer cap off the valve and follow the
Valve Adjustment procedure in Section 8.0.
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