AIR SYSTEM COMPONENTS
SUB-SECTlON 9C
unseat the Inlet valve. allowing air to flow through the valve
7. Reconnect the air lines to the outlet body.
to the throttle cylinder. Air flowing to the throttle cylinder
also acts on the top of the balance piston. When the air
8. Test the operation of the overhauled throttle valve by
pressure acting on the top of the balance piston exceeds the
performing the Operating and Leakage Test.
force applied to the bottom of the balance piston by the
spring, the balance piston moves downward, allowing the
ADJUSTMENT. The following adjustments should be made
cage to also move downward. Downward movement of the
after the value has been overhauled or replaced.
cage will block the flow of air through the valve, and the
valve is in a balanced condition.
NOTE
Disconnect the throttle linkage at the throttle cylin-
der, and use the throttle cylinder to determine when
the throttle valve is delivering air in the first adjust-
If the pressure at the throttle cylinder should decrease, the
ment. Reconnect the linkage before performing the
spring at the bottom of the balance piston will push the
second adjustment.
balance piston and cage upward, opening a passage which
will allow air to flow to the throttle cylinder. The balance
1. Adjust the stop screw under the heel of the pedal so that
piston will continue to move up and down, allowing and
the valve will deliver pressure as soon as the pedal is de-
blocking the flow of air through the valve, as the pressure
pressed. Run the screw up until pressure just begins to be
within the system varies or the operator changes the posi-
delivered to the throttle cylinder. Then turn it back until
tion of the hand lever.
pressure just shuts off. Tighten the locknut.
When the operator returns the hand lever to the off posi-
2. The upper throttle valve has an additional adjustment
tion, the piston moves upward, seating the inlet seat. Once
that is not required on the carrier throttle valve; namely, a
the inlet seat is seated, the air pressure acting on the under-
high speed limit adjustment. This adjustment is accom-
side of the seat will cause the cage to move upward,
plished by depressing the throttle pedal until the engine
unseating the exhaust seat. This will allow the air pressure
speed is increased to 2600 rpm, with no load applied to the
in the throttle cylinder to escape to atmosphere through
engine. Loosen the locknut and turn the adjusting screw
the valve.
under the toe of the pedal until it limits maximum engine
speed to 2600 rpm. lighten the locknut.
OPERATING AND LEAKAGE TEST. Perform the fol-
HAND THROTTLE VALVE (36U54)
lowing tests periodically to determine the serviceability of
the hand throttle valve.
DESCRIPTION. The hand throttle valve is an optional con-
trol unit of the air throttle system. It provides the operator
1. Coat the exhaust port of the hand throttle valve with a
with a means of setting and maintaining a desired engine
soap solution to determine If the valve is leaking when the
speed.
air system is fully charged and the hand lever is in the off
position, No leakage is permissible at this point. If the valve
When the hand lever is in the off position, the piston is held
leaks at the exhaust port, the valve cartridge is faulty. and a
up against the push rod by the air pressure acting on the
new valve cartridge should be installed or the complete
underside of the piston. The piston also lifts the cage,
valve should be replaced.
which opens the exhaust seat and closes the inlet seat of the
valve. This allows any air pressure in the throttle cylinder to
2. Have an assistant move the hand lever from the full on
be vented to atmosphere through the valve, and blocks the
to full off positions several times and observe the operation
flow of air from the supply tank through the valve to the
throttle cylinder (see Figure 9C-16).
of the throttle cylinder. The throttle cylinder should re-
spond smoothly to changes in hand lever position. If the
When the operator moves the hand lever to the on position.
throttle cylinder does not respond smoothly. the compen-
the cage is moved downward, seating the exhaust seat. Once
sating spring in the valve is broken, and the complete valve
the exhaust seat is seated, further downward movement will
should be replaced.
9C-18
