AIR -TVBC SYSTEM -TURBINE COOLING AIR (TCA) THERMOCOUPLE PROBE

EFFECTIVITY BEJ ALL  75-25-00 
Page 13 
D633W101-BEJ  Sep 05/2003 

AIR -TVBC SYSTEM -FUNCTIONAL DESCRIPTION

BEJ ALL POST SB 777-71-0032
General
The EEC uses the turbine cooling air thermocouple probe to monitor the temperature between the HPT 1st stage blades and the 2nd stage vanes to control the TVBC system. The EEC controls the TVBC air shutoff valve solenoid to open and close the TVBC air shutoff valves. The EEC also controls a torque motor that modulates the TVC air valve. The valves supply 12th stage cooling air for the different engine operating conditions.
BEJ ALL
General
The EEC uses the turbine cooling air thermocouple probe to monitor the temperature between the HPT 1st stage blades and the 2nd stage vanes to control the TVBC system. The EEC controls the TVBC air shutoff valve solenoid to open and close the TVBC air shutoff valves. The valves supply 12th stage cooling air for the different engine operating conditions.
BEJ ALL POST SB 777-71-0032
Control
The EEC sends a signal to a dual-coil torque motor in the TVC air valve actuator. This sets the position of a pilot valve. The pilot valve controls the servo fuel pressure that moves the actuator piston to modulate the TVC air valve.
Two LVDTs monitor the position of the piston. Each LVDT sends data to an EEC channel.
The EEC also sends a signal to the TVBC air shutoff valve solenoid. The solenoids control the PS3 air that closes the TVBC air shutoff valves and thrust balance air shutoff valve.
BEJ ALL
Control
The EEC sends a signal to the TVBC air shutoff valve solenoid. The solenoids control the PS3 air that closes the TVBC air shutoff valves and thrust balance air shutoff valve.
EFFECTIVITY BEJ ALL  75-25-00 
Page 14 
D633W101-BEJ  Jan 05/2004 

AIR -TVBC SYSTEM -FUNCTIONAL DESCRIPTION

BEJ ALL POST SB 777-71-0032
Normal Operation -Idle
When the engine is at idle power, the four valves are open to supply maximum cooling airflow to the 2nd stage vanes and blades, and turbine cavity seals.
BEJ ALL
Normal Operation -Idle
When the engine is at idle power, the valves are open to supply maximum cooling airflow to these:
*
2nd stage vanes and blades

*
3rd through 5th stage vanes

*
Number 3 bearing buffer cooler

*
Turbine cavity seals.

Normal Operation -Takeoff
During takeoff, the valves stay open to supply maximum cooling airflow.
BEJ ALL POST SB 777-71-0032
Normal Operation -Climb
During climb, the lower left TVBC shutoff valve and the TVC air valve are used to keep the turbine cavity seal temperature in limits. The other two shutoff valves stay open to cool the 2nd stage vanes and blades.
BEJ ALL
　
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