Hartzell HC-B3-2 Series Owner's Manual And Logbook page 81

In reverse mode of operation, the governor operates in
an underspeed condition to act strictly as a source of
pressurized oil, without attempting to control RPM. Control of
the propeller blade angle in reverse is accomplished through
the beta valve.
NOTE: The beta valve is normally located on the side of
the gearbox opposite the propeller.
The propeller is reversed by manually repositioning the
power lever within the beta range to cause the beta valve to
supply oil from the governor pump to the propeller. A beta
rod inserted into the front of the propeller communicates
propeller blade angle position to the beta valve. When the
propeller reaches the desired reverse position, movement of
the beta rod causes the beta valve to shut off the flow of oil
to the propeller. Any additional unwanted movement of the
propeller toward reverse, or any movement of the manually
positioned beta valve control toward high pitch position
will cause the beta valve to drain oil from the propeller to
increase pitch.
It is undesirable to feather the propeller when the engine
is stopped after landing the aircraft. This propeller type is
normally installed on a fixed shaft engine that causes the
propeller to rotate during an engine start process. If the
propeller is in feather position, an overload on the electric
engine starter will occur.
To prevent feathering during normal engine shutdown, the
propeller incorporates spring-energized latch pins called
start lock units. These units are installed either on a two-
piece spinner mounting plate or on the spinner bulkhead,
which is bolted to the propeller hub flange. If propeller
rotation is approximately 800 RPM or above, the start lock
units are disengaged from the blade clamp mounted plates
by centrifugal force acting on the latch pins to compress the
springs (within the units). When the RPM drops below 800,
the springs overcome the centrifugal force and move the
latch pins to engage the clamp-mounted plate, preventing
blade angle movement to feather.
DESCRIPTION AND OPERATION
Propeller Owner's Manual
139
61-00-39
Page 2-19
Rev. 17 Apr/20