DOC AIRBUS | AMM A320FTURBINE ACTIVE CLEARANCE CONTROL (ACC) - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
1. Component Location
** ON A/C NOT FOR ALL 
Air System (Active Clearance Control (ACC) System)- The turbine ACC air valve is located on the diffuser case at the 1 o'clock position.
| FIN | FUNCTIONAL DESIGNATION | PANEL | ZONE | ACCESS DOOR | ATA REF |
|---|---|---|---|---|---|
| ** ON A/C NOT FOR ALL | |||||
| 4055KS | TURBINE ACC AIR VALVE | 400 | 73-11-00 | ||
2. System Description
A. Turbine ACC System
(1) The ACC system is a dual channel Electronic Engine Control (EEC) controlled system.
(a) This system meters fan air onto the turbine case through external manifolds to manage High Pressure Turbine HPT and LPT blade tip clearance for better fuel efficiency.
(b) The ACC system actuator controls air flow to the HPT and LPT case cooling manifolds to minimize turbine blade tip clearance over the full engine operating range.
(c) The ACC valve is a fuel-actuated butterfly valve that controls cooling air to the turbine cases.
(d) The actuator lets fan bypass air cool and control the expansion of the turbine case to match the radial expansion of the rotor.
(e) Usually, the ACC valve is closed at start and idle, partially open at take-off and climb and fully open at cruise.
(2) The manifolds direct fan air onto the turbine case to decrease turbine case growth because of thermal expansion.
(3) The HPT manifolds and the LPT manifolds share a single control air valve and collector.
(a) Fan bypass air enters the inlet duct through the Inner Fixed Structure (IFS) of the nacelle and is supplied to the ACC air valve.
(b) The EEC controls the system on a schedule that is based on engine parameters and altitude.
(c) The EEC sends a milliampere signal to the torque motor which controls the fuel muscle pressure to put the actuator shaft in position. This shaft operates to open and close the air valve to control the flow of fan air onto the turbine cases. Feedback of actuator position is reported back to the EEC by a single channel Linear Variable Differential Transducer (LVDT).