Power Transfer Unit (PTU)
The PTU is a type of hydraulic pump which is able to transfer power but not the system fluid. It transfers hydraulic power between two different systems. Different types of PTUs are used by different aircraft manufacturer depending upon their designs and requirements. Some PTU (Power Transfer Unit) can only transfer power in one direction while others can transfer power in both directions. PTUs can have a fixed displacement or variable displacement hydraulic pump types. Within the PTUs, there are essentially two units: a hydraulic pump and a hydraulic motor, which are coupled by a single drive shaft to allow power to be transmitted between the two systems. Each unit functions as a motor or a pump depending on the direction of power transfer.
Airbus A320 Series PTU
The PTU (Power Transfer Unit) is a reversible hydraulic motor pump located between the green and yellow hydraulic systems in aircraft. PTU enables the Green hydraulic system to pressurize the Yellow hydraulic system and vice versa. When the pressure differential between the Green and Yellow hydraulic systems is more than the 500 PSI, the PTU is automatically activated. When the aeroplane is on the ground and the engines are turned off, the PTU allows the Yellow hydraulic system to pressurise the Green hydraulic system through the Yellow Electric pump. The hydraulic page of the ECAM (Electronic Centralized Aircraft Monitor) displays PTU operation.
The PTU is inhibited
When only one ENG MASTER switch is on and the PARK BRK is on
When only one ENG MASTER switch is on and the nose wheel steering disconnect pin is inserted
When the PTU is turned off
Note:
When the cargo doors are opened and closed (inhibition of PTU continues for approximately 40 seconds after cargo door operation)
Airbus A320 PTU Logics
Airbus a320 PTU Push Button
PTU PB SW Functions
The following are the functions of the PTU PB Switch:
AUTO Postion:
Both the yellow and green electrohydraulic valves are open, and the bidirectional power transfer unit is armed.
When the pressure differential between the green and yellow systems is more than the 500 PSI, the power transfer unit activates automatically.
Note : On the first engine start, the Power Transfer Unit (PTU) is inhibited, and it is also tested automatically during the second engine start.
OFF Postion:
Both the Green and the Yellow System PTU Electrohydraulic valves close.
Power transfer stops.
FAULT Light :
This amber fault light comes on, and a caution appears on the ECAM Page.
If: Any of the following occurred
The green or the yellow hydraulic reservoir overheats
The green or the yellow hydraulic reservoir has a low fluid level.
The green or the yellow hydraulic system reservoir has low air pressure
The Caution light goes out when the crew selects OFF the Push button, except during an overheat. (The Caution light stays on as long as the overheat lasts).
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