Power Transfer Of Hydraulic System A321

ATA29

General :

  • The aircraft has a power transfer system to transfer hydraulic power between the Green and Yellow systems. This is necessary if one of the engine pumps fails. It also makes it possible to pressurize the Green system from the Yellow system for maintenance (with the Yellow system electric pump).
  • The power transfer system is always armed when the hydraulic systems are pressurized. However, the crew can switch it off if necessary .The connection between the two systems is mechanical. It is impossible for fluid to get from one system to the other. When the isolation coupling is disconnected (during ground maintenance operations only), there is no transfer of power.

The primary components in the power transfer system are:

  • the Power Transfer Unit (PTU)
  • the Green-System solenoid valve
  • the Yellow-System solenoid valve
  • the isolation coupling
  • the PTU switch.

Power is automatically sensed and transferred through the PTU. A piston in the PTU’s control valve is exposed to the Green and Yellow system pressure. When the pressure difference between the Green and Yellow systems is more than 500 psi (34.5 bar), the PTU starts to operate.

Final Operation Procedure :

  • PTU transfer power from high pressure system to other system.
  • When yellow pump operate on ground , power supply to 3 solenoid valve ( Green solenoid valve ,yellow solenoid valve and solenoid valve of yellow-leakage measurement system ) , so hydraulic power doesn’t supply to green and yellow system.
  • The solenoid valve of the Green system is connected to the Green PTU manifold.
  • The solenoid valve of the Yellow system is connected to the Yellow PTU manifold.
  • The two solenoid valves operate at the same time and they are controlled by the PTU switch on the overhead panel 40VU.
  • There is no transfer of power when the isolation coupling is disconnected.

Component Description :

  • The PTU is made up of a variable displacement unit coupled to a fixed displacement unit. The variable displacement unit is connected to the yellow hydraulic system. The fixed displacement unit is connected to the green hydraulic system.
  • Displacement of the variable displacement unit is varied to maintain the required running and breakdown pressure differentials between systems. Displacement of the variable unit is controlled by means of a control which senses the system delta pressure.
  • The variable displacement unit is at maximum displacement during the power transfer from the Yellow to the Green system. Then it is at minimum displacement during the power transfer from the Green to the Yellow system.
  • The variable displacement unit includes a hydraulic servo valve and a variable cam. The servo valve gets input from the pressure differential, which starts the PTU. It controls the displacement of the variable cam which in turn gives the quantity of stroke ( quản lý số lượng hành trình của CAM ) . During PTU operation, the servo valve controls the pressure differential.
  • There are three hydraulic connections on the fixed displacement unit and three on the variable displacement unit. The connections are:
    • high pressure
    • low pressure
    • case drain.
  • A solenoid-controlled 3/2-way valve is installed in the PTU supply line of each system (Green and Yellow). They operate together to let the PTU operate or not-operate. When the solenoid valve is energized, the spool moves into the port to close the valve. When the solenoid is de-energized, the spool moves away from the port to open the valve. ( lưu ý : Valve này được mở khi solenoid không được cấp điện ).
Solenoid Valve
  • An isolation coupling is installed in the power transfer unit manifold (3015GM) of the Yellow hydraulic system. It is a quick-release coupling which seals automatically when it is disconnected. It also has a ratchet lock to keep it connected ( Lắp bên dưới PTU , bên phải nhìn từ đuôi máy bay lên ).
  • The usual flight condition is the PTU system “armed” (the P/BSW set to AUTO and both solenoid valves open) and the Green and Yellow hydraulic systems at the same pressure. Because the pressures of the two hydraulic systems are in 500 psi of each other, the PTU does not operate (transfer pressure) ( Trạng thái bình thường khi bay , PTU để vị trí AUTO , 2 solenoid valve de-energized và 2 valve này mở , cả 2 hệ thống đều có áp suất 500 psi , PTU sẽ hoạt động ).

Note about Seal Drain connection :

The seal drain system collects hydraulic fluid from the seal drains of specified components of the three hydraulic systems. The air relief valves of the reservoirs are also connected to the seal drain system. This is to collect any fluid which comes out of a reservoir if the pressure in the reservoir is too high. The fluid from a given component goes through a system of pipes to one of the two collector tanks. The tanks are the FWD collector tank and the AFT collector tank. The system also gives some protection if the reservoirs are overfilled. However, if there is an excessive flow of fluid, or if the collector tank is full, the fluid comes out of the overflow pipe. In this case the fluid is not contained and goes into the hydraulic compartment.

  • Case drain tube and Low pressure port , high pressure port connection
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