Hartzell HC-B3-2 Series Owner's Manual And Logbook page 73

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 built into the base of the
governor.
The propeller is reversed by manually repositioning the
cockpit-control to cause the beta valve to supply oil from
the governor pump to the propeller. An external propeller
feedback mechanism, which include a beta ring and carbon
block assembly, communicate propeller blade angle position
to the beta valve.
When the propeller reaches the desired reverse position,
movement of the beta ring and carbon block assembly,
initiated by the propeller piston, 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.
With some applications, it is undesirable to feather the
propeller when the engine is stopped after landing the
aircraft.
To prevent feathering during normal engine shutdown, the
propeller incorporates spring-energized latch pins called
start lock units (Figure 2-4). 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 2-11
Rev. 17 Apr/20