POWER TRANSFER UNIT (PTU)

The PTU is a bi-directional motor pump located between the green and yellow hydraulic systems. It enables either system to power the other in case of pump failure. The PTU is automatically activated if there is a pressure differential of 500 psi or more between systems. On the ground with the engines not running, the PTU can be used to power the green system by activating the yellow electric pump.

The PTU is automatically inhibited: 

• During the first engine start 

• When the cargo doors are operating 

• When the parking brake is on and only one engine is running 

• When the PTU switch is off

• The PTU is automatically tested during second engine start. If the second engine is started within 40 seconds of the cargo doors closing, a HYD PTU FAULT will be triggered. To reset the warning, switch the yellow electric pump ON and then OFF. (3.02.29 P16) 

• The PTU does not transfer fluid.

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