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TM 9-2330-380-14&P
4-43. Front Relay Valve
This task covers:
a. Operating test
b. Leakage test
c. Removal
d. Cleaning
e. Inspection
f. Installation
Initial Setup:
Tools/Test Equipment:
EquipmentConditions:
General mechanic's tool kit (item 01, Appendix B)
Towing vehicle attached and air brake system
charged.
Materials/Supplies:
Dry cleaning solvent (item 3, Appendix E)
Teflon tape (item 12, Appendix E)
Brush (item 15, Appendix E)
a. Operating test
1. With brake air system of semitrailer connected and charged, check if brakes apply properly.
2. Release brakes and check to see that air pressure is being exhausted promptly.
3. With semitrailer brake system fully charged, close shutoff valve in emergency line tube on
towing vehicle and disconnect brake air hose coupling tagged EMERGENCY. Check
whether semitrailer brakes apply automatically.
4. Connect brake air hose to coupling tagged EMERGENCY. Open shutoff valve on towing vehicle and
check for automatic release of brakes.
b. Leakage test
1. With brake air system of semitrailer connected and charged, apply soap and water solution to cover
flanges which hold diaphragms and to brake air hose coupling tagged SERVICE. No leakage should
be present. If leaks are detected, tighten attaching hardware and tighten coupling as required.
2. Apply brakes and apply soap and water solution to all air fittings and check for leaks.
3. Disconnect EMERGENCY coupling (step 3, operating test), coat exhaust port with soap and water
solution and test for leaks.
4. Leakage in steps 2 and 3 must not exceed one inch bubble in two seconds. If excess leakage is found,
replace relay valve.
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