Aneroid bellows assembly Poppet Poppet seat Adjustment screw Oil drain port Oil inlet port Dock pressure sensing port Manifold pressure sensing port Diaphragm Aneroid bellows assembly Oil restrictor valve Throttle controlled cam Engine oil from wastegate actuator Oil return to engine Upper deck pressure Figure 3-22.  A diagram of a sloped controller used to maintain the  rated compressor discharge pressure at wide-open throttle. Figure 3-21.  A diagram of a variable absolute pressure controller  (VAPC). guide only and should not be substituted for applicable  manufacturer’s instructions or troubleshooting procedures. sensitive to the throttle differential pressure than to deck  pressure, thereby accomplishing deck pressure reduction as  the throttle is closed. One device used to control the speed and output of the  turbocharger, but controls the system only at maximum  output, is the absolute pressure controller. The absolute  pressure controller contains an aneroid bellows that is  referenced to upper deck pressure. It operates the wastegate,  which diverts, more or less, exhaust gas over the turbine.  As an absolute pressure setting is reached, it bypasses  oil, and relieves the pressure on the waste gate actuator.  This allows the absolute pressure controller to control the  maximum turbocharger compressor discharge pressure. The  turbocharger is completely automatic, requiring no pilot  action up to the critical altitude.  The engine inlet of a turbine engine is designed to provide a  relatively distortion-free flow of air, in the required quantity,  to the inlet of the compressor.  [Figure 3-24]  Many engines  use inlet guide vanes (IGV) to help straighten the airflow and  direct it into the first stages of the compressor. A uniform and  steady airflow is necessary to avoid compressor stall (airflow  tends to stop or reverse direction of flow) and excessive  internal engine temperatures in the turbine section. Normally,  the air-inlet duct is considered an airframe part and not a  part of the engine. However, the duct is very important to  the engine’s overall performance and the engine’s ability to  produce an optimum amount of thrust. Figure 3-23  includes some of the most common turbocharger  system malfunctions together with their cause and repair.  These troubleshooting procedures are presented as a  A gas turbine engine consumes considerable more airflow  than a reciprocating engine. The air entrance passage is  correspondingly larger. Furthermore, it is more critical in  determining engine and aircraft performance, especially  at high airspeeds. Inefficiencies of the inlet duct result in  successively magnified losses through other components of  3-17 Turbine Engine Inlet Systems Absolute Pressure Controller  Turbocharger System Troubleshooting