BENDIX SR-4 SPRING BRAKE CONTROL VLV Manual
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®
™
Bendix
SR-4
Spring Brake Control Valve
#1
RESERVOIR
CHARGING
PORT
DELIVERY PORTS (4)
FIGURE 1A
™
FIGURE 1 - SR-4
SPRING BRAKE CONTROL VALVE TYPE 1 & TYPE 2
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
similar in appearance to an SR-2
subassembly is an SR-2
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
identifi ed by the metal tag affi xed to the cover by one of
four cap screws. Porting is as follows:
#2 RESERVOIR
CHARGING
PORT
SERVICE PORT
TRAILER SUPPLY
PORT
TYPE 1
™
valve sub-assembly
™
valve. The SR-4
™
valve modifi ed by the addition
™
valve may be
#1
RESERVOIR
CHARGING
PORT
DELIVERY
PORTS (4)
FIGURE 1B
• 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
™
valve
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
#2 RESERVOIR
CHARGING
PORT
SERVICE PORT
TRAILER SUPPLY
PORT
TYPE 2
1