at the forwardmost end indicating EMERG
electrical or manual pitch change command.
AHEAD.
If the command is for pitch change ahead,
control oil is ported to the forward control
oil chamber; the aft control oil chamber
CONTROL VALVES MANIFOLD
port is open to return, causing the piston
BLOCK ASSEMBLY
assembly to move forward. This translates
the valve rod forward, resulting in propeller
On the OD box is a manifold block assembly.
pitch change in the ahead direction. As the
This assembly houses the two four-way change-
piston assembly moves forward, the oil in
over valves, the electrohydraulic servo control
the aft control oil chamber is displaced through
valve, and the manual control valve. It is
the aft chamber port by the aft piston. If the
referred to as the control valves manifold block
command is for pitch change astern, control oil
assembly and is shown in figure 8-24. Its function
is ported to the aft control oil chamber and the
is to direct the flow of control hydraulic oil from
action is reversed. The oil flow directions are
the HOPM to the control oil section of the OD
indicated in figure 8-23.
box. It responds to an electrical or manual input
to control propeller pitch.
The piston assembly is mechanically connected
to the valve rod by a bearing assembly and
The two four-way changeover valves are
distance tube. The bearing assembly is necessary
used to select the operating mode. Each valve has
for the transfer of the axial forces since the piston
a selector handle with a pointer and a dial. The
is stationary, while the distance tube and valve
dials are labeled MAN-OFF-AUTO. Both selector
rod rotate with the propeller shaft. The bearing
handles must be placed in the same mode for
assembly also absorbs the thrust load of the valve
proper operation of the system. The OFF position
rod.
of the changeover valves is used only when they
are being operated with the emergency pitch
If a failure of the normal pitch control system
positioner.
occurs, an emergency system is provided. The
control valves and emergency pump assemblies
In the AUTO (automatic) mode, the electro-
are shown in figure 8-24. A hand-operated
hydraulic control oil servo valve directs the
hydraulic pump can be connected to the
control oil flow to the OD box. It responds to an
emergency ahead and astern control oil ports
electrical signal from the electronic pitch control
located adjacent to the normal ports. A four-way
unit located in each engine room.
selector valve on the emergency pump is used to
In the MAN (manual) mode, the manual
direct pump output pressure to the forward or aft
control valve directs the control oil flow to the
control oil chamber for the desired pitch. A
OD box in response to movement of the valve
locking device on the OD box end cover enables
lever. The manual control valve has a control
the propeller to be locked in the emergency ahead
handle with three positions labeled AHEAD,
position for sustained operation. In the locked
OFF, and ASTERN. The control handle is spring-
position, a machined shoulder on the locking
loaded in the OFF (center) position. Movement
device mechanism within the OD box engages the
of the control handle in the desired direction, that
forward piston and mechanically locks the piston
is, AHEAD or ASTERN, will result in a pitch
in posit ion.
change. It is held in that position until the desired
pitch has been attained. When the desired pitch
A follow-up rod is connected to the forward
has been reached, the handle is released. It returns
piston and extends through a penetration in the
to the OFF position by the spring force, and the
end cover. Externally, the follow-up rod is
propeller pitch holds at the new position.
connected to a local pitch indicator and two
sliding-contact potentiometers mounted on top of
the OD box. The potentiometers provide feedback
HYDRAULIC OIL POWER SYSTEM
and pitch readout signals to the electronic pitch
control system. The local pitch indicator is a
The purpose of the hydraulic oil power system
pointer which slides along a scale calibrated
is to supply both HP hydraulic oil for propeller
in feet of pitch. The indicator scale extends over
blade actuation and control oil for propeller pitch
the end of the OD box and reads from 15 feet
control. A schematic of the hydraulic oil system
astern to 28 feet ahead. It has a separate notch
8-36
