control oil system, the power oil system, and the
described previously. The only difference is that
return oil system. In the following section, we will
the valve is operated manually through a lever,
as opposed to the servo control valve which is
describe these systems.
operated electrically through a solenoid.
The emergency pitch connections are used
CONTROL OIL.--Control oil from the
when control oil or HP oil are not available from
HOPM enters the OD box through the control
the HOPM. As seen in figure 8-23, the emergency
valves manifold block assembly. Figure 8-26
connections supply oil to the OD box piston in
shows the control oil line entering the control
valves manifold block assembly and dividing with
the same manner as the normal connections. The
two separate flow paths. One leads to the
difference is that the control oil must be supplied
electrohydraulic servo valve and the other leads
from a special hand pump and a much higher
to the manual control valve. The outflow lines of
pressure is required.
these valves meet at two changeover valves. One
POWER OIL.--High-pressure hydraulic oil
changeover valve allows oil to pass in or out of
from the HOPM enters the OD box through a
the astern OD box piston chamber through a
flange connection on the bottom aft section (fig.
single line. The other changeover valve allows flow
8-23). The flange passes the oil to an annular
into or out of the forward OD box piston chamber
channel in the stationary HP seal assembly. The
through a single line. Each changeover valve
determines which control valve (servo or manual)
HP seal ring, which seals the top of the annular
channel, is attached to the OD box shaft. As the
outflow is going to pass through to the OD box.
OD box shaft turns, the HP seal ring rotates in
With the changeover valves in the MANUAL
the top of the channel. Holes drilled through the
position, only the control oil passing through the
HP seal ring and continuing through the OD box
manual control valve can pass through the
shaft conduct the HP oil from the annular
changeover valves to the OD box. The AUTO
channel in the HP seal assembly to an annular
position passes only the control oil from the
electrohydraulic servo valve. When the change-
chamber formed between the OD box shaft and
the distance tube. This chamber directs the oil
over valves are in the OFF position, no oil can
slightly aft to where it enters the regulating valve
flow in or out of the OD box except through the
emergency hand pump connections.
rod through two drilled passages. The HP oil then
continues through the valve rod to the propeller
During normal control oil flow, with the
hub.
changeover valves in the AUTO position, the
servo control valve is opened by signals from the
RETURN OIL.--Return oil from the hub,
electronic pitch control system to increase pitch
which is called LP oil, flows forward through the
in the astern direction. Control oil flows through
passage between the outside surface of the valve
the servo control valve and the astern changeover
rod and the inside surface of the propeller shaft.
valve to the astern pitch connection on the
The return oil enters the OD box through six
bottom side of the OD box. Entry of oil into the
astern piston chamber causes the piston assembly
passages drilled in the OD box shaft between the
to move aft, thus translating the valve rod for a
propulsion shaft and the OD box shaft extension.
The six passages direct the oil to a relatively large
pitch change astern. As the piston assembly moves
annular return oil chamber. Any leakage past the
aft, the oil in the forward piston chamber is
HP seal also enters the return oil chamber. Return
pushed out through the forward pitch connection
oil is discharged from the return oil chamber back
located on the top side of the OD box. This return
to the CRP sump through a flange connection.
control oil flows out through the forward
This flange connection is located just forward of
changeover valve to the servo control valve. It
the HP oil inlet connection.
then passes to the return oil line that leads back
The CRP head tank connects to the return oil
to the sump.
If ahead pitch is ordered, the servo control
chamber through a flange located on the top aft
valve switches the flow path. This causes oil to
section of the OD box. This location places the
enter the forward pitch connection on the OD box
head tank above the OD box. The overflow line
allows the 65-gallon tank to hold 40 gallons before
rather than the astern pitch connection. Oil
passing oil back to the sump. The purpose of the
returns from the astern pitch connection, and the
flow is reversed from the situation described in
head tank is to maintain a static head pressure
the previous paragraph. The manual control valve
on the oil in the propeller hub when the hydraulic
directs the control oil flow in the same way as
system is shut down. This prevents seawater from
8-40
