SUB-SECTION DC
AIR SYSTEM COMPONENTS
8. Install the new clevis on the end of the piston rod. Screw
move downward. Downward movement of the cage will
the clevis on the piston rod as far as it will go. Install the
block the flow of air through the valve, and the valve is in a
dust boot over the clevis.
balanced condition.
9. Position the cylinder lever on the cylinder and connect it
If the pressure at the throttle cylinder should decrease, the
with new clevis pins and cotter pins. After the cylinder
spring at the bottom of the balance piston will push the
lever is installed on the cylinder, tighten the jam nut to lock
balance piston and cage upward, opening a passage which
the clevis in position.
will allow air to flow to the throttle cylinder. The balance
piston will continue to move up and down, allowing and
10. Install a new diaphragm over the piston as shown in
blocking the flow of air through the valve, as the pressure
Figure 9C-14. Be sure the lip on the diaphragm is properly
within the system varies or the operator changes the position
seated in the body groove.
of the pedal.
11. Install the cover over the diaphragm, and secure the
When the operator releases the pedal, the piston moves up
cover with new machine screws.
ward, seating the inlet seat. Once the inlet seat is seated, the
air pressure acting on the underside of the seat will cause
INSTALLATION. To install a new or overhauled throttle
the cage to move upward, unseating the exhaust seat. This
cylinder, proceed as follows (sea Figure 9C-13):
will allow the air pressure in the throttle cylinder to escape
to atmosphere through the valve.
1. Position the cylinder on the mounting plate, and install
the mounting capscrews, lockwashers, and nuts.
OPERATING AND LEAKAGE TEST. Perform the fol-
lowing tests periodically to determine the serviceability of
2. Connect the throttle link to the cylinder lever, and pin
the throttle valve.
the throttle link in place on the cylinder lever.
1. Coat the exhaust port of the throttle valve with a soap
3. Connect the air line to the cylinder.
solution to determine if the valve is leaking when the air
system is fully charged and the throttle pedal is in the
4. Check the operation of the cylinder by performing the
released position. No Ieakage is permissible at this point. If
Leakage Test.
the valve leaks at the exhaust port, the valve cartridge is
faulty, and a new valve cartridge should be installed or the
THROTTLE VALVE (36U29)
complete valve should be replaced.
DESCRIPTlON. The air throttle valve is the control unit of
2. Have an assistant depress and release the throttle pedal
the air throttle system. It provides the driver with an easily
several times and observe the operation of the slave cylin-
operated and graduated means of increasing or decreasing
der. The slave cylinder should respond smoothly to changes
the engine speed.
in throttle pedal position. If the throttle cylinder does not
respond smoothly, the compensating spring in the throttle
When the valve pedal is in the released position, the piston
valve is broken, and the complete valve should be replaced.
is held up against the push rod by the air pressure acting on
the underside of the piston. The piston also lifts the cage,
OVERHAUL. Overhaul of this valve should be limited to
which opens the exhaust seat and closes the inlet seat of the
the replacement of the parts furnished in the repair kit for
valve. This allows any air pressure in the throttle cylinder to
this valve. To overhaul the valve, proceed as follows (see
be vented to atmosphere through the valve, and blocks the
flow of air from the supply tank through the valve to the
throttle cylinder (see Figure 9C-15).
1. Disconnect the air lines attached to the outlet body of
the valve. Remove the six body screws and remove the
When the operator depresses the pedal, the cage is moved
outlet body. Remove the barrier plate assembly and lift out
downward, seating the exhaust seat. Once the exhaust seat
the balance piston. The barrier plate assembly may be dis-
IS seated. further downward movement will unseat the inlet
carded, as a new assembled replacement is included in the
valve, allowing air to flow through the valve to the throttle
repair kit.
cylinder. Air flowing to the throttle cylinder also acts on
the top of the balance piston. When the air pressure acting
2. Remove the balance spring and wear shim from the out-
on the top of the balance piston exceeds the force applied
let body. Wash the parts in cleaning solvent. Then inspect
to the bottom of the balance piston by the spring, the
the outlet body for excessive wear in the area where the
balance piston moves downward, allowing the cage to also
piston contacts the body bore.
9C-16
