Hydraulics

Question 1

Typical hydraulic pressures? (With RAT operating?)

Answer 1

3000psi +/- 200psi (2500psi)

Question 2

How does hydraulic system generate pressure?

Answer 2

Green- engine 1 driven pump
Yellow- engine 2 driven pump (or electric pump/hand pump)
Blue- Electric pump (or RAT)

PTU can pressurise green or yellow system in event of failure of engine pump

Question 3

What is the hydraulic accumulator and which system supplies it?

Answer 3

Accumulator is a way of storing hydraulic pressure when there is no other pressure available (parking brake)

Powered by yellow

Question 4

What are the priority valves?

Answer 4

Priority valves protect against low pressure by prioritising the low pressure is used to power important systems like flaps/slats, emergency generator and landing gear

Question 5

How are reservoirs pressurised?

Answer 5

Bleed air from engine 1.

If engine 1 failed, uses crossbleed air from engine 2.

Prevents cavitation

Question 6

Which systems have fire shut off valves?

Answer 6

Yellow and green

Question 7

How does PTU function during engine start procedure?

Answer 7

PTU inhibited during first engine start, self tests during 2nd engine start

Question 8

When does PTU operate?

Answer 8

Operates when differential pressure of more than 500psi between yellow and green.

Inhibited during 1st engine start and for 40s after cargo door ops