ADVANCE DIRECTIONAL VALVE
The advance directional valve (see fig. 4-45)
controls the hydraulic motor during advance. When
actuated by fluid flow from the pilot valve, the advance
directional valve piston shifts, directing fluid flow
through the directional valve to the hydraulic motor.
The fluid returns from the motor and flows through the
directional valve to the gravity tank. When the advance
directional valve is not actuated, no fluid flow is
allowed through the valve. As the traverse carriage
nears the end of an advance stroke, a cam mounted on
the carriage actuates the advance dump valve. This
drains the pressure in the advance directional valve
actuating chamber back to the gravity tank through the
dump valve. The advance directional valve piston then
closes, causing a gradual cutoff of hydraulic fluid from
the hydraulic motor, initiating retraction engine
braking.
MANEUVERING VALVE
The maneuvering valve (see fig. 4-45) is mounted
on the manifold and is operated by the maneuver
forward solenoid (EF) and the maneuver aft solenoid
(EA).
The
maneuvering
valve
is
energized
automatically during the latter part of the advance and
retract stroke to control the speed of the grab after
braking has been completed. Orifices control hydraulic
fluid flowing through the valve to and from the
hydraulic motor. At times other than during normal
operations, the valve can be energized to slowly
maneuver the grab, shuttle, and pistons forward or aft
for testing or maintenance. A manual override button
on the valve can be pushed to maneuver the grab aft in
case of power failure and permit disengagement of the
aircraft from the shuttle.
DUMP VALVES
The two dump valves (fig. 4-46) are mounted on
the retraction engine frame. The valves are actuated by
cams mounted on the traverse carriage. When the
retraction engine nears the end of the advance stroke,
the advance dump valve is actuated. The dump valve
closes allowing the pilot-actuating fluid from the
advance directional valve to return to the gravity tank,
initiating the advance braking stroke. When the
4-38
TO ADVANCE
DIRECTIONAL VALVE
TO RETRACT
DIRECTIONAL VALVE
FROM ADVANCE AND
RETRACT PILOT VALVE
FROM ADVANCE AND
RETRACT PILOT VALVE
RETRACTION DUMP
VALVE (C/23)
CABLE TENSIONER
ASSEMBLY (REF)
ADVANCE DUMP VALVE (C/24)
TO GRAVITY TANK
TO GRAVITY TANK
ABEf0447
Figure 4-46.—Retraction engine dump valves.
