SERVICE MANUAL
the spring above piston "A! forces it into contact with inlet
exhaust valve "A" causing the exhaust to seal and inlet to
open.
Fig. 3 Initial Air System Charge Below 55 PSI
1Primary Reservoir
2Secondary Reservoir
3Inlet & Exhaust A
4Piston A
5Piston B
6Check Valve
7Exhaust
8Inlet & Exhaust B
9Spring Brake Control Valve
10Double Check Valve
System Fully Charged (Fig. 4)
When
the
air
pressure
builds
up
past
the
approximate 379 kPa (55 psi) in both the primary and
secondary reservoirs, piston "A" has moved against the
force of the spring above it permitting the inlet of valve
"A" to close and open the hollow exhaust passage
through piston "A."
When air pressure under piston "B" is about 655 kPa
(95 psi), piston "B" raises slightly against the force of
springs above it allowing the inlet of valve "B" to close.
The exhaust through valve "B" remains closed. The
closing of inlet portion of valve "B" traps about 655 kPa
(95 psi) in the hold-off cavity of the spring brake
actuators while allowing full air system pressure to build
elsewhere.
Normal Brake Application with Primary and
Secondary Reservoirs Charged (Fig. 5)
When the service brakes are applied by ac-
tuating the dual brake valve, air from the secondary
system is delivered from the brake valve to the control
port where it is stopped at the closed inlet valve "A." No
further
movement
of
internal
components
of
the
inversion valve takes place. Air from the primary delivery
system of the brake valve actuates the service brakes of
the spring brake chambers.
Fig. 4 Air System Fully Charged
Fig. 5 Normal Broke Application, Primary and
Secondary Systems Charged
1Primary Reservoir
2Secondary Reservoir
3Inlet & Exhaust A
4Piston A
5Piston B
6Check Valve
7Exhaust
8Inlet & Exhaust B
9Spring Brake Control Valve
10Double Check Valve
Brake Application with Loss of Air in Secondary
System (Fig. 6)
If air pressure is lost in the secondary reservoir, the
primary reservoir as well as the spring brake control
valve is protected against air loss through action of single
check valve (air source to primary reservoir) and double
check valve (Fig. 6). A brake application at brake valve in
this situation results in little or no air being delivered from
the secondary system to the control port of inversion
valve. No movement of the internal components of the
valve takes place. Braking is assured since the primary
reservoir is protected and the primary delivery system of
the brake valve will apply the service brake portion of the
spring brake chambers.
CTS-4079 - CHAPTER VII - Page 4