HP Compressor Airflow Control System


This system consists of :

  • The Variable Stator Vane Actuator
  • The HPC bleed air tubes and the HPC stage 7 and 10 solenoid valves and bleed valves.
  • The variable stator vanes and the 7th and 10 t stage HP compressor bleeds are used to improve engine performance and stability during engine starting, acceleration and deceleration.
  • The variable stator vanes are modulated open or closed by a hydraulic actuator controlled by the Electronic Engine Control (EEC).
  • The 7th and 10th HP compressor bleed valves are pneumatically actuated by two position air shut-off valves which are actuated by EEC solenoids.

Variable Stator Vane System :

Airflow through the compressor is controlled by variable inlet guide vanes ( VIGVs) , variable stator vanes ( stage 3, 4, and 5 variable stators ) and bleed valves.

VSV System have the purpose of this system is to position the Inlet Guide Vanes (IGV) and stator vanes ( stage 3, 4, and 5 variable stators ) , using a fuel driven hydraulic actuator, in response to electrical signals provided by the EEC.

The engine IGV and Stator Vane linkage is connected to a fork end on the piston rod of the VSVA unit. The securing pin of link on to fork end.

The variable geometry operating mechanism for the compressor comprises the following elements:

  • actuator/crankshaft drag link
  • crankshaft (steel)
  • four crankshaft/unison ring drag links
  • four unison rings
  • spindle levers (titanium)
  • variable IGVs and stage 3, 4, and 5 variable stators (nimonic).
  • The movement of the actuator is transmitted to the crankshaft lever by a drag link.
  • The resultant rotation of the crankshaft is also transmitted from levers to the four unison rings ( 4 vòng tròn đồng tâm ) by drag links .All the drag-links are constructed in heat-resistant steel (Jethete)( thép chịu nhiệt ) and are configured with spherical rod ends ( rod ends hình cầu ) of left-hand and right-hand threads.

HP Compressor Bleed Valves System :

HP compressor bleed valves are required for stability of engine operation during starting and transient conditions.

  • Three bleed valves for the seventh stage.
  • one for the tenth stage of the HP compressor redirect a portion of HP compressor air into the fan stream.

The bleed valves are mounted onto the outside of the HP compressor case. Each valve has a spring loaded open position. The piston has holes to permit a flow of air through the valve when it is open. When the valve is closed the piston is held against a plate which is part of the valve body. This shuts off the air bleed from the compressor.The piston is held in the open position by spring and compressor delivery (P3) pressures. When the P3 pressure is released by the controlling solenoid valve, the bleed valve is closed by compressor air pressure.

Each air bleed valve has its own controlling solenoid valve which is installed on the fan case. The solenoid valve is connected to the bleed valve by a tube. This tube transmits P3 pressure to or from the bleed valve. The solenoid valve is controlled by electrical signals from the EEC through two separate coils.With either or both of the solenoid coils energized, the service port is connected to vent. In this position the bleed valve is held closed.With both solenoid coils de-energized the solenoid valve connects the engine supplied air to the service port holding the bleed valve open.The accessories which do the power distribution are divided into four groups: engine group I, engine group II, autostart group and reverser group.

HPC Stage 7 Solenoid Valves

HPC Stage 10 Bleed Valve Solenoid

Stage7:-Air is supplied at high power setting for aircraft needs (using anti-icing, cabin pressurization and heating).Air is also bled off to aid starting and handling by maintening compressor surge margin. At all power settings the nose cowl is supplied with anti-icing air from this stage.

Stage 8:-Air is bled internally and is used to seal the LP turbine compartment. The air cools the rear of the stage 2 HP turbine disc and the LP turbine drum internally. It is also used to pressurize the number 5 bearing compartment.

Stage 10:-Air is supplied when power settings are low for aircraft needs (using anti-icing, cabin pressurization and heating).Air is also bled off to aid starting and handling by maintaining compressor surge margin. HP turbine cooling air is supplied at all power settings. A further controlled supply is taken to the stage 2 HP turbine front face.

Compressor outlet:-Air is tapped via tubes to an air cooled air cooler and is fed to the centre air supply (stage 12) bearing buffer cooling zone of the number 4 bearing. Control of the air bleed system and the variable stator vanes is by the Electronic Engine Control (EEC).

(a) Although allowing the air bleed on the IP port of the engine, the solenoid when energized permits to control closure of the HP Bleed Valve.The solenoid is mounted on the fan case on each engine.

(b) Operation : The solenoid is energized/de-energized in reponse to EEC signals.When the unit is de-energized, the valve seals the HPV to PRV sense line, the internal parts of the solenoid are at atmospheric pressure.Energizing the unit opens the valve allowing air to flow from the HPV to PRV sense line to atmosphere.

Final :

  • Khi 1 hoặc cả 2 solenoid được energize , service port trên solenoid vent to áp suất môi trường , khi đó đường vent của HPV và PRV cũng vent ra bên ngoài. Khi đó buồng opening của HPV sẽ không được cấp khí , HPV sẽ đóng do khí cấp vào buồng close của HPV. Lúc này Bleed valve cung bị đóng lại bởi khí từ compressor, ngắt khí từ compressor cấp cho bleed.
  • Khi cả 2 solenoid bị de-energize , HPV và PRV vent line sẽ bị seal lại , lúc đó áp suất khí sẽ mở buồng open của HPV , áp suất khí đầu ra HPV sẽ trích 1 phần đi vào buồng close của HPV , duy trì áp suất đầu ra của HPV từ 8 đên 36 psi. Bleed valve cũng sẽ mở để thoát khí nén ra khi khí bleed không cần nhiều.

When the solenoid is de-energized, the opening of the HP VLV is not
. The solenoid will be energized by the BMC/EEC (depending
on the engine type) when:
– the engine is above idle, the pressure PS3 is greater than 110 psi for the
single aisle family IAE V2500 engines, or 80 psi for the CFM-56 engines.
– the Wing Anti-Ice (WAI) is OFF,
– the altitude is over 15,000 ft,
– the pack configuration is normal.

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