Failures

In case of refuse EDP of Yellow, hydraulic system (Figure 5) starts to fall the pressure in the system. When the pressure in Yellow system decreases to 2500 PSI automatically activated PTU

Figure 5 – Failure of ADP.

Also failure of the EDP using a running ELEC (Figure 6)in the Yellow HS pressure is maintained constant.

Figure 6

In case failure of PTU when the pressure falls to 1440, “failure” light illuminates (Figure 7), and turn on ELEC

Figure 7

In case failure of both EDP (Figure 8) the pressure falls, turn on ELEC of Yellow system in this system pressure rise up, and activated the PTU which increases pressure in Green system

Figure 8 Failure of both EDP

Power Transfer Unit (PTU)
When only 1 engine is running, it can provide hydraulic power to the whole system through the Power Transfer Unit. For example, if engine 1 is stopped, the Green hydraulic circuit is not pressurized any more and the hydraulic pressure decreases. When it is lower than a specific threshold, the PTU activates to transfer
hydraulic pressure from the Yellow circuit to the Green circuit, allowing all the hydraulic systems to keep working.
The PTU generates a very typical sound that the passengers can hear in the cabin.