Torque Limiter - Textron Cessna Grand Caravan Ex 208B Pilot's Operating Handbook And Faa Approved Airplane Flight Manual

CESSNA
MODEL 208B 867 SHP
GARMIN G1000

TORQUE LIMITER

The torque limiter installed on the engine is a mechanical back-up unit
which prevents unintentional engine overtorques. On the PT6A-140
engine it limits the maximum torque value to 2500 FT-LB regardless of
propeller RPM.
The backup unit incorporates an oil bellows which senses torquemeter
oil pressure and is linked to a Py bleed orifice. Oil from the torquemeter
chamber passes through a restrictor before entering the bellows. The
restrictor dampens torque pressure fluctuation and prevents damage to
the bellows assembly. When torque pressure reaches 2500 FT-LB, the
bellows expands and compresses the spring.
Bimetallic disks are mounted on the spring to compensate for variation
of spring tension caused by change in ambient temperature.
The flapper valve then moves to allow Py air pressure from the fuel
control unit to vent to the atmosphere and therefore limit the fuel supply
to the engine reducing the engine speed and subsequently reducing
torque.
The pilot is always responsible for operating the engine
torque within limits and not depend on the mechanical
torque limiter.
208BPHCUS-00
AIRPLANE AND SYSTEMS DESCRIPTION
CAUTION
SECTION 7
7-71
U.S.