Bendix SR-1 SPRING BRAKE VALVE User Manual
Bendix® SR-1™ Spring Brake Valve
SD-03-4508
1/4 P.T.
RES. #1
1/4 P.T.
CONTROL
FIGURE 1 - EXTERIOR VIEW
1/4 P.T.
DELIVERY
1/4 P.T.
SUPPLY
VALVE SPRING (11)
VALVE STOP (10)
FIGURE 2 - SECTIONAL VIEW
DESCRIPTION:
The SR-1™ spring brake valve is used in dual or “split” air
brake systems equipped with spring brake actuators. The
function of the SR-1™ valve is to supply a specific, limited
hold-off pressure to the spring brakes, and in the event of
loss of No. 1 service air pressure, to modulate the spring
brakes through the use of the service brake valve.
The valve has four identified 1/4" N.P.T.F. ports and a
diaphragm protected exhaust port. T wo 5/16" diameter holes
are provided in the integral mounting bracket of the valve
body . The SR-1™ valve must be mounted with the exhaust
port down toward the road surface.
OPERATION - INITIAL AIR SYSTEM CHARGE
Upon initial charge, air from #1 & #2 service reservoirs flows
through the park control valve and enters the SR-1™ valve
supply port. Air entering the supply port flows past inlet and
exhaust valve B to the underside of piston B and out the
delivery port of the SR-1™ valve to the emergency air
connection at the spring brake actuator. Note that the springs
above piston B force it into contact with inlet and exhaust
valve B. In the position shown the exhaust is closed and the
inlet is open.
PISTON
SPRINGS (14)
(6)
COVER (5)
O-RING
(LARGE)
(SMALL) (19)
VALVE SPRING (2)
PIPE PLUG
EXHAUST
PISTON SPRING
(14)
PISTON (15)
PISTON O-RINGS
(16)
VALVE (12)
O-RING (9)
CAP NUT
(8)
COVER (13)
INLET &
EXHAUST
VALVE (7)
DIAPHRAGM
Air flowing from the No. 1 reservoir only enters the reservoir
port of the SR-1™ valve. This air remains under piston A as
system pressure builds. With No. 1 reservoir pressure below
approximately 55 P.S.I. the spring above piston A forces it
into contact with inlet and exhaust valve A causing the
exhaust to seal and the inlet to open.
With air system pressure above approximately 55 P.S.I. in
No. 1 & 2 service reservoirs, piston A has moved against
the force of the spring above it, allowing the inlet of valve A
to close and opening the hollow exhaust passage through
piston A.
OPERATION - AIR BRAKE SYSTEM FULLY
CHARGED
When air pressure beneath piston B is approximately 95*
P .S.I., piston B rises slightly , against the force of the springs
above it, allowing the inlet of valve B to close. The exhaust
through valve B remains closed. The closing of the inlet
portion of valve B retains approximately 95* P.S.I. in the
hold- off cavity of the spring brake actuators while allowing
full air system pressure to build elsewhere.
*Note: Other spring brake hold-off pressures are supplied
according to the vehicle manufacturer’s
specifications. 95 P.S.I. was chosen only for the
purpose of explanation.
(18)
PISTON (17)
O-RING
BODY
CHECK
VALVE (4)
CHECK
(1)
1
MODULATOR
™
PP-7
CONTROL
VALVE
PARK
CONTROL
LQ-4
™
VALVE
DS-1
DOUBLE
CHECK
VALVE
TP-3
LP-3™ INDICATOR
#2 SERVICE
RESERVOIR
™
TRACTOR PROTECTION VALVE
SB-3 SB-3
™
R-8
VALVE
™
R-8
VALVE
FIGURE 3 - PIPING DIAGRAM
#2 SERVICE
RESERVOIR
#1 SERVICE
RESERVOIR
SUPPLY
RESERVOIR
#1 SERVICE
RESERVOIR
PISTON A
INLET &
EXHAUST A
SB-3 SB-3
PISTON B
CHECK VALVE
DOUBLE
CHECK
VALVE
PARK
CONTROL
FIGURE 4 - CHARGING - BELOW 55 P.S.I.
2
SB-3
INLET
&
EXHAUST
B
EXHAUST
#2 SERVICE
RESERVOIR
PISTON A
PISTON B
#1 SERVICE
RESERVOIR
DOUBLE
CHECK
VALVE
FIGURE 5 - SYSTEM FULLY CHARGED
#2 SERVICE
RESERVOIR
#1 SERVICE
RESERVOIR
PARK
CONTROL
INLET &
EXHAUST A
PISTON A
CHECK VALVE
INLET &
EXHAUST
B
EXHAUST
SB-3
PISTON B
CHECK VALVE
INLET &
EXHAUST A
DOUBLE
CHECK
VALVE
FIGURE 6 - NORMAL SERVICE APPLICA TION
PARK CONTROL
OPERATION - NORMAL SERVICE
RESERVOIRS 1 & 2 CHARGED
When a service application is made by actuating the dual
brake valve, air from the No. 2 delivery circuit is delivered
from the brake valve to the control port, and is stopped at
the closed inlet of valve A. No movement of the internal
components of the SR-1™ valve takes place. Air from the
No. 1 delivery circuit of the dual brake valve actuates the
service section of the spring brake actuators.
INLET
&
EXHAUST
B
EXHAUST
SB-3
OPERATION - SERVICE APPLICATION WITH
LOSS OF NO. 2 RESERVOIR PRESSURE
In the event air pressure is lost in the No. 2 reservoir, the No.
1 reservoir and the parking control valve will be protected via
the double and single check valves in the air system. A
service application of the foot brake valve in this situation
results in little or no air being delivered from the No. 2 delivery
circuit to the control port of the SR-1™ valve. No movement
of the SR-1™ valve internal components takes place. Braking
is assured because the No. 1 service reservoir is protected
by a check valve and the No. 1 delivery circuit of the dual
3
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