TM 9-2330-294-14
Adjust valve if required, (3) below. Replace valves
become locked in applied position refer to table 4-4.
(3) Test while parked. Life front suspension
that cannot be adjusted to requirements.
a n d perform following tests, then, lift rear
NOTE
Incorrect readings may be obtained if
system air pressure is below normal. If low
malfunction is found.
pressure is measured at several regulator
(a ) Man in towing vehicle cab applies brakes
valves, check for obstruction in air supply
while two men try to turn raised semitrailer wheel(s).
line(s) to air control valve.
Wheel(s) should not turn.
(3) Regulator Valve Adjustment. Adjust each
(b ) While brakes remain unapplied two men
regulator valve by loosening jam nut which locks
try to turn raised trailer wheel(s). Wheels should
turn.
to increase pressure, counterclockwise to reduce
c. Air Suspension System Tests, Checks and
pressure. Tighten jam nut when required pressure is
A d j u s t m e n t s . Refer to
figure 4-59 and 4-60 to
obtained.
identify air suspension air lines and components.
d. Air Lines Leakage Test and Inspection. I f
NOTE
leaks are suspected, coat air lines, couplings, and
No test should be made on the air suspension
connections with soapy water and watch for bubbles.
system unless full air pressure (90 - 120 psi)
Tighten fittings on lines and hoses that show
is available in the reservoir air line.
evidence of leaks. Inspect lines for partial restric-
(1) Operating Check.
tions caused by dents or kinks. Inspect hose
(a) Assure suspension air shutoff valves (fig.
assemblies for wear, cuts, or breaks. Replace tubing,
2-8) are open on empty semitrailer. Move suspension
hose, or fitting if damaged, or if leak cannot be
air control valve to LIGHT LOAD position. Observe
stopped. Whenever nylon tubing is replaced be sure
that air springs are inflated. Check 15 psi regulator
to add inserts to tube ends, otherwise leakage will
valve for correct pressure setting (2) below.
occur.
(b) Move suspension air control valve handle
e. Air Tank Leakage Test. With air system
to HALF LOAD position. Observe that air springs
charged, coat drain cocks and tubing connections
expand. Walk around semitrailer and listen for air
with soapy water. No leakage is permissible. Tighten
leakage. Check 50 psi regulator valve for correct
any leaking connections. Inspect tanks for damage
pressure setting (2) below.
or corrosion. Replace tanks that leak, are damaged
(c) Move air control valve handle to FULL
or are corroded. Open drain cocks slightly on air
LOAD position. Observe that air springs expand and
tanks daily and allow moisture to drain. Close drain
raise forward tandem wheels several inches off
ground. Check 85 psi regulator valve for correct
cocks after draining.
preesure setting (2) below.
f. Emergency Relay Valve Operation and Tests.
(1) Purpose (fig. 4-27 and 4-28). The relay
(d) Move air control valve handle to NO
valves (2) are connected with the service and
LOAD position. Listen at air control valve for
venting of air from the air springs. Observe the front
emergency air lines, the air reservoirs, and the brake
air chambers. The valves function to speed brake
tandem lower and the rear tandem raise ap-
operations and to apply brakes if the semitrailer
proximately three inches off the ground. Test 100 psi
becomes separated from the towing vehicle.
regulator valve for correct pressure setting (2) below.
(2) Operation during pressure build-up.
Refer to table 4-4 if malfunction is found in any
check (a ) through (d) above.
(a) Up to 45 psi, system air enters the
emergency relay valve through the emergency air
(2) R e g u l a t o r V a l v e P r e s s u r e S e t t i n g
line and is distributed to the semitrailer air reser-
Check. Apply accurate air gage (recently
voirs and to the service brakes, keeping them ap-
calibrated) to each suspension regulator valve air
plied.
(b) Above 45 psi, system air enters the relay
pressure requirements:
valve through the emergency air line, but is directed
Air Control Valve at LIGHT
only to the semitrailer reservoirs. Service brakes are
LOAD Position
1535 psi
released.
Air Control Valve at HALF
LOAD Position
(3) Operation after pressure build-up.
50&5 psi
Air Control Valve at HALF
(a) During brake application, the emergency
relay valve receives a pressure signal from the
LOAD Position
855 psi
towing vehicle service air line and supplies system
Air Control Valve at NO
1005 psi
air from the semitrailer reservoirs to the semitrailer
LOAD Lift Position