AIR BRAKES - GENERAL INFORMATION
DETAILED OPERATIONAL CHECK OF TRAILER
SUPPLY AND PARK BRAKE SYSTEMS
Modular Control Valve
Use two air test gauges 0-1103 kPa (0-160 psi)
or Duplex gauge (SE-2325) with hoses and two
emergency); attach the gauges to service and
emergency couplings on vehicle.
With the trailer supply knob (red) and parking
brake knob (yellow) out, charge primary and
secondary air systems to 448 kPa (65 psi).
Push red knob in. The red knob should remain in
and air pressure at instrument panel and test
gauge at trailer emergency port should read
approximately the same. Test gauge at service
connection should show no pressure.
Push yellow knob in and apply foot valve to
deplete air supply. The red knob should pop out
when the reservoir with the highest pressure
reaches 276 + 27.6 kPa (40 + 5 psi). The red
knob could pop immediately if air is depleted
Apply foot valve to further deplete air pressure.
Air should escape the exhaust port of the trailer
supply portion of valve. When air pressure in
reservoir with the higher pressure reaches 207 +
27.6 kPa (30 + 5 psi), the yellow knob may pop
out (park brake application).
Deplete the air system even further using foot
valve. At 172 + 27.6 kPa (25 + 5 psi), the yellow
knob must pop out (park brake application).
Rebuild air supply to at least 276 kPa (40 psi),
push yellow knob in. It should remain in.
Push red knob in and pull yellow knob out. The
red knob must pop out almost instantaneously.
Rebuild air supply to 689-861 kPa (100-125 psi)
in both primary and secondary reservoirs. Push
red and yellow knobs in. Pressure at trailer
emergency connection should equal pressure in
Pressure at trailer emergency connection should
descend to 724-621 kPa (105-90 psi) at which
point the double check valve in the modular
control valve should switch to the secondary
reservoir and pressure at emergency connection
should adjust (equalize) to secondary reservoir
pressure. Close off leak at primary reservoir.
With the red knob in and the hand control valve
released, apply brake valve. Pressure at trailer
service should be within 27.6 kPa (5 psi) of
gauge at instrument panel.
Replenish air system to 689-861 kPa (100-125
pressure with yellow knob in. As the secondary
descend, between 793-724 kPa (115-105 psi)
the double check shuttle in the valve should
switch to the primary reservoir and the pressure
should adjust to the primary reservoir pressure.
With the red knob pushed in, disconnect the
trailer emergency coupling from the test gauge.
The red knob should pop out instantaneously. If
emergency coupling to gauge.
Replenish air in system. With the red knob in,
apply the hand control valve. There should be a
minimum of 586 kPa (85 psi) at trailer service
Release hand control valve and apply foot valve.
Pressure at service port should be within 35 kPa
(5 psi) of the pressure indicated at
Close all vents or leakage points and charge
system to 689-861 kPa (100-125 psi). Apply
brake valve, pull red knob out (yellow knob in).
connection should record the same value (689-
861 kPa or 100-125 psi) as gauge at instrument
panel. Gauge at emergency connection should
With red knob out and yellow knob in, develop a
leak in the spring brake delivery (line) and hold
yellow knob in. The primary reservoir pressure
must reduce to zero and secondary reservoir
pressure to 138-207 kPa (20-30 psi). The
double check valve in the modular control should
cycle several times during the leak down period.
If the foregoing checks perform as described,
the chassis is ready for service. Remove air test
gauges from trailer couplings.
If the operational checks revealed malfunctions within
the system, a more detailed investigation of components
will be required. Refer to COMPONENTS Section for
detailed information regarding service check on various
Separate Spring Brake and Tractor Protection
Using two air gauges (0-160 psi) or Duplex
gauge (SE-2325*) with hoses and two additional
trailer couplings (service and emergency), attach
the air gauges to the service and emergency
couplings on vehicle.
Build up air pressure in chassis air system.
* At one time the Sealco duplex air gauge (model 110122) was available under Tool Equipment No. SE-2325.
CTS-4154Y - Page 21