Bendix Commercial Vehicle Systems SR-1 SPRING BRAKE VALVE - Manual (Page 5)

5
OPERATION - SERVICE APPLICATION WITH LOSS
OF NO. 1 RESERVOIR PRESSURE
If air pressure in the No. 1 service reservoir falls below
approximately 55 P.S.I., the pressure beneath piston A is
insuffi cient to resist the spring force above and piston A moves
into contact with valve A. Initial contact between piston A
and valve A closes the hollow exhaust passage of piston A.
Continued movement of the piston opens the inlet of valve A.
The No. 2 service reservoir and the park control valve are
protected from pressure loss by the action of the double
check valve.
When a service application of the dual brake valve is
made, air delivered from the No. 2 delivery circuit of the
dual brake valve enters the Bendix
® SR-1 ™ valve control
port. Air entering the control port moves past the inlet of
valve A and is conducted through a passage in the body to
the underside of piston B. The air pressure moves piston
B up, opening the exhaust of valve B. When the exhaust
of valve B opens, air pressure trapped in the emergency
section of the spring brake actuator is allowed to escape,
resulting in an emergency brake application. The air
pressure released from the spring brake is proportional
to the air pressure delivered to the control port of the
SR-1 valve by the No. 2 delivery of the dual brake valve.
FIGURE 8 - SERVICE APPLICATION - LOSS OF #2 RESERVOIR
FIGURE 9 - SERVICE APPLICATION - LOSS OF #1 RESERVOIR
#2 SERVICE
RESERVOIR
#1 SERVICE
RESERVOIR
DOUBLE
CHECK
VALVE
PISTON B
CHECK VALVE
INLET &
EXHAUST A
PISTON A
INLET
&
EXHAUST
B
EXHAUST
SPRING
BRAKE
#2 SERVICE
RESERVOIR
#1 SERVICE
RESERVOIR
DOUBLE
CHECK
VALVE
PISTON B
CHECK VALVE
INLET &
EXHAUST A
PISTON A
INLET
&
EXHAUST
B EXHAUST
SPRING
BRAKE
R-14 ®
RELAY
VALVE
R-14 ®
RELAY
VALVE
PARK
CONTROL
VALVE
PARK
CONTROL
VALVE