Hartzell HC-E4 3 Series Owner's Manual page 67

If governor supplied oil is lost during operation, the propeller
will increase pitch and feather. Feathering occurs because the
summation of internal propeller forces causes the oil to drain
out of the propeller until the feather stop position is reached.
Normal in-flight feathering is accomplished when the pilot
retards the propeller condition lever past the feather detent.
This permits control oil to drain from the propeller and return to
the engine sump. Engine shutdown is normally accomplished
during the feathering process.
Normal in-flight unfeathering is accomplished when the pilot
positions the propeller condition lever into the normal flight
(governing) range and restarts the engine. As engine speed
increases, the governor supplies oil to the propeller and the
blade angle decreases.
In reverse mode of operation, the governor operates in an
underspeed condition to act strictly as a source of
pressurized oil, while attempting to control RPM. Control
of the propeller blade angle in reverse is accomplished
with the beta valve for propellers with beta feedback block
assemblies and with the PCU for propellers with electronic
beta sensors.
NOTE: For installations with beta feedback block
assemblies, the beta valve is normally built into the
base of the governor. For installations with beta
sensors, the beta valve function is built into the
PCU control system.
For installations with beta feedback block assemblies,
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. Several external propeller
mechanisms, which include a beta ring and beta feedback
block assembly, communicate propeller blade angle position
to the beta valve.
DESCRIPTION AND OPERATION
Propeller Owner's Manual
147
61-00-47
Page 2-11
Rev. 17 Sep/20