DOC AIRBUS | AMM A320FAUXILIARY HYDRAULIC POWER - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
1. General
The auxiliary hydraulic power systems are those which supply the aircraft when the supply from the main pumps is not available. The auxiliary systems and their related main systems are:
There is also a hand pump (Ref. AMM D/O 52-36-00-00) which supplies the hydraulic power of the cargo compartment doors only.
The power transfer system has a Power Transfer Unit (PTU) which transfers hydraulic power (in either direction) between the Green and Yellow hydraulic systems. The connection between the Green and Yellow sides of the PTU is mechanical. Thus no hydraulic fluid can get from one system into the other. Operation of the power transfer system is automatic, with the PTU armed all of the time. The PTU starts to operate when one of the two hydraulic systems has a pressure approximately 500 psi (34.47 bar) less than the other system.
Operation of the PTU can be stopped (or the PTU can be disarmed) from the flight compartment if required. The PTU can also be isolated hydraulically for maintenance to make it possible to pressurize only the Green or the Yellow hydraulic system.
The RAT supplies the Blue main hydraulic system with hydraulic power. Deployment of the RAT into the airflow is automatic when there is a total loss of AC power (when the aircraft speed is greater than 100 kts). The flight or the maintenance crew can deploy the RAT from the flight compartment. When the RAT deploys automatically (or by use of the ELEC OVRD switch), the constant speed motor/generator (CSM/G) also automatically operates. Thus, the aircraft is supplied with electrical power and the Blue main system is pressurized. Once deployed, hydraulic power is necessary to retract the RAT. It is only possible to retract the RAT when the aircraft is on the ground.
The electric pump of the Yellow auxiliary hydraulic system can also supply the Yellow main hydraulic system with hydraulic power. Operation of the pump is not automatic, the pump is switched on from the flight compartment. On the ground, the electric pump supplies the Yellow main hydraulic system and, through the PTU, also supplies the Green main hydraulic system.
On the ground, the electric pump starts automatically (when the aircraft has AC power) if the cargo compartment doors are set to open or close. At the same time, the PTU and the flight control circuits of the Yellow hydraulic system are isolated. Thus, there is no danger of movement of the flight controls when the hydraulic system is pressurized.
The auxiliary hydraulic power systems are those which supply the aircraft when the supply from the main pumps is not available. The auxiliary systems and their related main systems are:
- the Blue auxiliary system (Ram Air Turbine (RAT) (Ref. AMM D/O 29-22-00-00), which supplies the Blue hydraulic system,
- the power transfer (Ref. AMM D/O 29-23-00-00), between the Green and the Yellow hydraulic systems,
- the electric pump (Ref. AMM D/O 29-24-00-00), which supplies the Yellow hydraulic system.
There is also a hand pump (Ref. AMM D/O 52-36-00-00) which supplies the hydraulic power of the cargo compartment doors only.
The power transfer system has a Power Transfer Unit (PTU) which transfers hydraulic power (in either direction) between the Green and Yellow hydraulic systems. The connection between the Green and Yellow sides of the PTU is mechanical. Thus no hydraulic fluid can get from one system into the other. Operation of the power transfer system is automatic, with the PTU armed all of the time. The PTU starts to operate when one of the two hydraulic systems has a pressure approximately 500 psi (34.47 bar) less than the other system.
Operation of the PTU can be stopped (or the PTU can be disarmed) from the flight compartment if required. The PTU can also be isolated hydraulically for maintenance to make it possible to pressurize only the Green or the Yellow hydraulic system.
The RAT supplies the Blue main hydraulic system with hydraulic power. Deployment of the RAT into the airflow is automatic when there is a total loss of AC power (when the aircraft speed is greater than 100 kts). The flight or the maintenance crew can deploy the RAT from the flight compartment. When the RAT deploys automatically (or by use of the ELEC OVRD switch), the constant speed motor/generator (CSM/G) also automatically operates. Thus, the aircraft is supplied with electrical power and the Blue main system is pressurized. Once deployed, hydraulic power is necessary to retract the RAT. It is only possible to retract the RAT when the aircraft is on the ground.
The electric pump of the Yellow auxiliary hydraulic system can also supply the Yellow main hydraulic system with hydraulic power. Operation of the pump is not automatic, the pump is switched on from the flight compartment. On the ground, the electric pump supplies the Yellow main hydraulic system and, through the PTU, also supplies the Green main hydraulic system.
On the ground, the electric pump starts automatically (when the aircraft has AC power) if the cargo compartment doors are set to open or close. At the same time, the PTU and the flight control circuits of the Yellow hydraulic system are isolated. Thus, there is no danger of movement of the flight controls when the hydraulic system is pressurized.