DUAL BRAKE VALVE
Prior to installing the valve on the crane, all
connecting air lines should be inspected for kinks,
The dual brake valve is mounted to the cab floor. It
is a treadle-operated type brake valve with two
of these deficiencies should be replaced.
separate supply and delivery circuits. The valve
provides the driver with a graduated control for
Position the valve on the mounting and secure
applying and releasing the vehicle brakes.
The circuits in the dual brake valve are identified as
Connect the air lines to the proper port on the
follows. The No. 1 circuit portion is that portion of
valve in accordance with identification marks made
the valve between the spring seat which contacts
the plunger and the relay piston. The No. 2 circuit
portion is that portion between the relay piston and
Perform the procedures under Operating and
the exhaust cavity.
The No. 1 circuit portion of the valve is similar in
operation to a standard single-circuit air brake
valve and under normal operating conditions the
No. 2 circuit portion is similar in operation to a relay
Chock the wheels and fully charge the air
system. Adjust the brakes.
Both the No. 1 and No. 2 circuit portions of the dual
brake valve use a common exhaust protected by an
Apply and release the brakes several times
and check for prompt response of the brakes at all
Chock the wheels.
With the dual brake valve in the brake released
Deplete all pressure in both air systems.
position, coat the exhaust port with a soap solution to
check for inlet valve and O-ring leakage. A 1 in. (254
Identify, mark, and disconnect all air lines from
cm) bubble in five seconds is permitted.
the brake valve.
Place the dual brake valve in the brake applied
Remove the three bolts, lockwasher, and nuts
position and again check at the exhaust port for
securing the brake valve and treadle assembly to the
leakage of the exhaust valve. Apply a soap solution
cab floor. Remove the brake valve and treadle
around the valve where the cover joins the body to
assembly as a unit.
check for seal ring leakage. A 1 in. (254 cm) bubble
in three seconds is permitted.
With the dual brake valve still in the brake
The basic brake valve alone can be
applied position, apply the soap solution to the quick
removed by removing the three
release exhaust port on the R-12 valve to check the
capscrews on the inner bolt circle.
diaphragm exhaust seat, and to the valve body in the
area where the cover joins the body on the R-12
valve, to check for cover O-ring leakage. No leakage
Position the brake valve and treadle assembly
in the cab floor opening and secure it with the three
If the valve does not function as described above, or
if leakage is excessive, it is recommended that the
valve be repaired or replaced.
Connect the air lines to the proper ports on the
valve in accordance with the identification marks
made during removal.