2
FIGURE 2 - SECTIONAL VIEW AR-2
™
ANTILOCK RELAY VALVE
CONTROL PORT
PROPORTIONING
PISTON
INLET/EXHAUST VALVE
AR-2
™
VALVE
AIR CONNECTION
EMBOSSED IDENT.
Supply (to reservoir)
SUP
Delivery (to brake chamber)
DEL
Service (to brake valve rear service delivery)
SER
Control (to delivery of trailer supply valve)
CON
The AR-2
™
valve is part of the R-12
™
family of relay valves
which includes the R-12
™
, R-14
™
, BP-R1
™
, and AR-1
™
valves.
The internal components of the relay portion of all of these
valves are interchangeable with the R-12
™
valve and therefore
the same basic components are used to service all of them.
The AR-2
™
valve incorporates various crack pressures to
accommodate specific applications, the standard is 4 psi.
OPERATION
GENERAL
Because the AR-2
™
valve is actually a relay valve, the
following description of operation refers to its function in the
vehicle’s air brake system and does not address the separate
antilock components and their operation. For a description
of antilock operation refer to the appropriate Service Data
Sheet covering the electronic controller used with the AR-2
™
valve (ie; SD-13-4785 covering the EC-15
™
electronic
controller). Other useful information regarding antilock
system components used in conjunction with the AR-2
™
valve is contained in publications SD-13-4793 covering the
M-21
™
antilock modulator and SD-13-4754 covering the
WS-20
™
wheel speed sensor.
INITIAL CHARGING
During the initial build up of tractor system air pressure,
reservoir air flows into the supply port and through internal
body and cover passages to the blend back piston. When
sufficient air pressure is applied to the blend back piston, it
moves against the resistance of its spring until it comes to
rest against the service piston.
Activating the trailer supply valve (dash control with red
octagonal button), simultaneously charges the trailer and
the AR-2
™
valve control port. Air entering the AR-2
™
valve
control causes the proportioning piston to move toward its
stop in the cover. The integral inlet and exhaust valve is
carried along with the piston until it seats and seals the
exhaust passage. Continued movement of the proportioning
piston opens the inlet seat. With the tractor and trailer air
system fully charged the vehicle may be operated.
SPRING (NOT IN ALL
MODELS)
RELAY PISTON
SERVICE PISTON
SERVICE PORT
SPRING
BLEND BACK
PISTON
EXHAUST
INLET/EXHAUST VALVE
SUPPLY PORT
EXHAUST
DELIVERY PORT
