PTUThe PTU is an auxiliary pressure supply for either the green or yellowsystems without transfer of fluid between the two systems.It operates automatically if there is a delta pressure of 500psi betweenthe green / yellow or yellow / green hydraulic systems.The side operating as a pump will take fluid from its associatedreservoir and provide an output through the PTU manifold to the HPmanifold.The motor side is supplied from the HP manifold through the PTUmanifold, and is connected to the return system. The PTU isde-activated by closing the solenoid valves on the PTU manifolds.Each section of the PTU has a case drain connection to the returnsystem.On the yellow system the normal source of pressure is the EDP and asauxiliary sources the PTU and the electric pump (E- Pump).NOTE: The yellow system also has a hand pump dedicated to cargodoor operation.