1
SD-03-4514
Bendix
®
SR-4
™
Spring Brake Control Valve
DESCRIPTION
The SR-4
™
valve is provided in two different confi gurations.
Type 1 (Fig. 1A) incorporates a nipple mounted PR-3
™
valve. Type 2 (Fig. 1B) has the function of the additional
PR-3
™
valve integrated into the main housing. There is
no difference in the operational performance of the two
designs.
The SR-4
™
trailer spring brake control valve is similar
to the SR-2
™
valve. It differs in function by utilizing both
reservoirs for normal service braking but reserving suffi cient
air pressure to provide the required spring brake release in
the event of a service system failure. As seen in Fig. 1, the
complete assembly includes an SR-4
™
valve sub-assembly
similar in appearance to an SR-2
™
valve. The SR-4
™
valve
subassembly is an SR-2
™
valve modifi ed by the addition
of a check valve in the spring brake reservoir fi tting which
permits air to pass from the reservoir to the spring brake
inlet valve but not in the opposite direction. AT NO TIME
SHOULD AN SR-2
™
VALVE BE SUBSTITUTED FOR THE
SR-4
™
VALVE SUBASSEMBLY. The SR-4
™
valve may be
identifi ed by the metal tag affi xed to the cover by one of
four cap screws. Porting is as follows:
• 1/2 inch NPT or 3/4 inch NPT spring brake supply port
for reservoir mounting
• 4-3/8 inch NPT delivery ports
• 2-1/4 inch NPT reservoir charging ports
• 1-1/4 inch NPT trailer supply port
• 1-1/4 inch NPT service port (optional)
OPERATION (FIG. 2)
CHARGING
Air from the trailer supply line enters at the trailer supply port
and depresses the control piston "D", opening the spring
brake inlet valve "E". It also is conducted to the cavity under
the pressure protection piston "F". When air pressure builds
to approximately 60 p.s.i. beneath the pressure protection
piston, the piston moves against the force of the pressure
protection spring and opens the pressure protection inlet
valve. The air pressure now fl ows past check valve “A”
into the #2 reservoir and past check valve “B” through the
open spring brake inlet valve and into the spring brake
FIGURE 1
- SR-4
™
SPRING BRAKE CONTROL VALVE TYPE 1 & TYPE 2
#2 RESERVOIR
CHARGING
PORT
DELIVERY PORTS (4)
TRAILER SUPPLY
PORT
#1
RESERVOIR
CHARGING
PORT
SERVICE PORT
#2 RESERVOIR
CHARGING
PORT
DELIVERY
PORTS (4)
TRAILER SUPPLY
PORT
#1
RESERVOIR
CHARGING
PORT
SERVICE PORT
FIGURE 1A
FIGURE 1B
TYPE 1
TYPE 2
