ATA 29: Airbus A320 (Technical Notes)

ATA 29 – HYDRAULIC POWER

MAIN SYSTEMS

Normal system operating pressure is 3000 PSI
- 2500 PSI when powered by the RAT (CSM/G).
Hydraulic fluid cannot be transferred from one system to another.
- Power can be transferred using PTU.

AUXILIARY SYSTEMS

SYSTEM NUMBERING

GROUND USE ONLY

Blue E-Pump – Override p/b switch for ground use only
Yellow E-Pump – only operates when engines are stopped. P/B or Cargo Door Selector – ON.
Yellow Sys Hand Pump – only for cargo door operations.
PTU can be used on ground to pressurized Green System using Yellow Electric Pump.
Blue and yellow electric pumps are interchangeable.

HYDRAULIC COMPONENTS LOCATIONS

MANIFOLDS

Manifolds make it possible to install different components on the manifold.
Replacement of components is possible with minimum effect on other components or pipes.
GREEN – HP Manifold, LP Manifold, PTU Manifold
YELLOW – HP Manifold, LP Manifold, PTU Manifold, Brake Manifold
BLUE – HP Manifold

USERS

Flight controls, Landing gear, Brakes, Nose wheel steering, Cargo doors, Thrust reverser, and CSM/G.
- GREEN – Normal Brake, L/G, TR1, Flaps, Slats, Yaw Damper 1.
- YELLOW – Alternate Brake, NWS, Cargo Doors, TR2, Flaps, Yaw Damper 2.
- BLUE – CSM/G, Slats.
Services which are not used during flight (cargo doors, brakes, landing gear and nosewheel steering) are isolated from the main supply.

PRIORITY VALVES

In the event of low hydraulic pressure, the priority valves maintain the operation of essential systems by cutting off hydraulic power to heavy load users.
It makes sure that all available hydraulic pressure is sent to the primary flight controls if pressure in the system is reduced.
The threshold of the priority valve is 1842 psi.
GREEN – priority valve is installed on the PTU manifold.
YELLOW – priority valve is installed on the PTU manifold.
The priority valve has three modes of operation:
- Full system pressure, the valve is open and fluid goes from port A (inlet) to port B (outlet),
- System pressure low, the valve is closed and fluid cannot get from port A to port B,
- More pressure downstream of the valve (at port B) than in the main system. The valve lets fluid flow from port B to port A.
Priority valve is a kind of sequence valve.

LEAK MEASUREMENT VALVES

The return flow of a hydraulic system is equal to the user’s demand flow plus the permanent internal leakage. The flight controls users are permanently supplied through leak measurement valves. These valves are electrically powered to the closed position for leak measurement test.
Each system has a leak measurement valve upstream of the primary flight controls.
Measure the leakage in each circuit. (Green, Yellow, and Blue circuits).
Can be closed by p/b switches on the maintenance panel.
Installed in the HP manifold of the respective system.

RESERVOIR PRESSURIZATION

Reservoir is pressurized by air at 50 psi to prevent cavitation.
Reservoir Pressurization Unit.
Normally, HP bleed air from engine 1 pressurizes the hydraulic reservoirs automatically.
- Higher line pressure than crossbleed duct (65psi).
- 65 PSI > Pressure Reducing v/v > 50 PSI
If the bleed air pressure is too low, the system takes bleed air pressure from the crossbleed duct.
Low air pressure warning at < 22 psi.
2 water drain valves – 1 automatic, 1 manual.
Can be pressurized using ground connection in the Reservoir Pressurization Unit.
The non-return valves are in each reservoir supply manifold. >> Pressure maintained –
- for up to 12 hours after engine shutdown on ground, and
- for up to 3 hours after a failure of the air supply in flight.

ACCUMULATOR

1.1 L
maintain a constant pressure by covering transient demands during normal operation.
precharged with nitrogen to 1885 psi at 20°C.

FIRE SHUT-OFF VALVE

PTU

A bidirectional power transfer unit enables the yellow system to pressurize the green system and vice versa.
PTU = Pump <> Motor
Electrohydraulic valves – 2, (for green & yellow) — controls the operation.

FILTERS

HP filter – in pressure line of G/Y/B SYS
- + Reservoir filling system
- + Normal braking system
LP filter – in return line line of G/Y/B SYS
Case Drain filter – in case drain line of both EDPs.
- + blue electric pump
Yellow E-Pump does not have a case drain line because it’s not a continuous running pump.

SEAL DRAIN

Hydraulic fluid that may escape from some hydraulic components in the form of leak or abnormal condition is drained into collector tanks.
Collector tank: 0.75 L

GREEN SYSTEM CONSUMERS

Direct from the EDP (upstream of the priority valve):
- LH (No. 1) engine thrust reverser.
From the HP manifold
- LH and RH spoiler 1 & 5
- LH and RH aileron
- LH and RH slat WTB
- RH flap WTB
- LH elevator
- Rudder
- THS
- Yaw damper
From the PTU manifold (downstream of the priority valve):
- PTU
- RH slat power control unit (PCU) motor
- LH flap PCU motor
- nose landing gear and doors
- main landing gear and doors.
From the PTU manifold (upstream of the priority valve):
- normal braking system.

YELLOW SYSTEM CONSUMERS

Direct from the EDP/electric pump/ground supply,
- RH (No. 2) engine thrust reverser
From the HP manifold
- LH and RH spoiler 2,
- LH and RH spoiler 4,
- LH flap WTB,
- RH elevator,
- Rudder,
- THS,
- Yaw damper.
From the HP manifold
- FWD and AFT cargo doors,
- Brake manifold,
- Nosewheel steering.
From the brake manifold,
- Alternate and parking brakes.
From the PTU manifold (downstream of the priority valve)
- PTU,
- RH motor of flap PCU.

BLUE SYSTEM CONSUMERS

From the HP manifold, downstream of the priority valve:
- LH slat PCU motor
- CSM/G.
From the HP manifold, upstream of the priority valve:
- LH & RH spoiler 3
- LH & RH ailerons
- LH & RH slat WTB
- LH & RH flap WTB
- LH & RH elevators
- Rudder
From the HP manifold, upstream of priority valve:
RAT

Training Points

There is no cooling system in hydraulic system. In case of overheat, ON the pumps for recirculation.
Hydraulic servicing panel – there is No Bypass filter, if popout change filter, no hydraulic will be uplifted.
Locking tool for depressurisation valve – for prolong maintenance.
Sometimes we see hydraulic fluid indication on ecam is more than the limit – fluid expanded due to high temperature.
HYD SYS – Phosphate eater base
L/G – Mineral base.
Torque link damper – ??
Case drain filter – do not reset ; open filter to check.
White tag – ecam indication
Blue tag – ??

COMPUTERS