Hydraulic system

           HYDRAULIC SYSTEM'S

✈The word hydraulics is based on the Greek word for water, and originally meant the study of physical
behavior of water at rest and in motion.

✈BASIC COMPONENTS
☂The basic components of any hydraulic system are reservoirs, filters, and pumps (hand or power-driven).
☂The reservoir holds the fluid supply for the system and helps cool the fluid.
☂Filters are used to ensure
that no contamination reaches the components in a hydraulic system.
☂The pleated micronic filter is the
most common.

✈Hydraulic fluid & Quantity
- (EXXON HYJET5-SKYDROLLD4)

✈The aircraft has three independent hydraulic systems:- (FOR A320)
☂green
☂yellow
☂blue.
✈Each system has its own hydraulic reservoir 
✈Power supply
☂The three hydraulic systems supply Normal hydraulic power at 3000 psi to the users:- 
  ⛑Flight controls
 ⛑Landing gear
 ⛑Brakes
 ⛑Nose wheel steering
 ⛑Cargo doors
 ⛑Thrust reverser operation
 ⛑Constant Speed Motor / Generator (CSM/G).

☂In an emergency, the blue system can be pressurized by the Ram  Air Turbine (RAT).    ⛑The RAT is deployed automatically or              manually.
  ⛑It pressurizes the blue hydraulic                  system at 2500 psi.

✈Hydraulic fluid cannot be transferred from one system to another.

✈System pressurization source
 ⛑WHY?:- A reservoir in each hydraulic system is pressurized with air to prevent cavitation.

☂Green System :- Two Source
     ⛑Engine Driven Pump(1)
     ⛑Power Transfer Unit (PTU)

☂Yellow System:- four source
     ⛑Engine Driven Pump(2)
     ⛑Electric Pump
     ⛑Hand Pump for cargo door OPS.
     ⛑Power Transfer Unit (PTU).
☠ Yellow system mainly used on ground for maintenance and cargo door operation.

☠If No electric power is available, a hand pump in the yellow system can be used to operate the cargo doors.
☂Blue System :- Two source
     ⛑Electric Pump
     ⛑Ram Air Turbine(RAT) - In emergency            only

☠Blue Electric Pump operates all the time in-flight and on the ground when at least one engine is operating.

☠The RAT and Yellow electric pumps do not normally run during flight( used on ground only).

✈PUMP
☂The heart of any hydraulic system is the pump which converts mechanical energy into hydraulic energy.
☂The source of mechanical energy is
⛑electric motor
⛑engine driven
⛑the operator's muscle.

Pumps powered by muscle are called hand pumps.


✈POWER TRANSFER UNIT (PTU)

☂A bidirectional power transfer unit enables the yellow system to pressurize the green system and viceversa.

☂The power transfer unit (PTU) comes into action automatically when the differential pressure between the green and the yellow systems is greater than 500 PSI.

☂The PTU therefore allows the green system to be pressurized on the ground when the engines are stopped.

☂PTU is able to transfer the power but not fluid.

✈RAM AIR TURBINE (RAT)

☂RAT is a small unit having to small aerofoil shaped blade which installed in it.
☂ it is deployed to the incoming airstream,
the blades rotate at high speed providing
emergency drive for the blue hydraulic system pressure pump.
☂RAT is automatically deployed
 if it senses
⛑ Both hydraulic system EDPs failed and           loss of pressure
⛑ Failure of both AC bus 1 and 2.
⛑ Aircraft speed is above 100 knots.

✈It can be deployed manually from the overhead panel. It can be stowed only when the aircraft is on the ground.

The RAT hydraulic pump is for emergency use only and will only deploy manually for hydraulic problems.
☂ For electrical problems it will deploy automatically above 100 kts. with loss of all AC bus.
☂Note: Min RAT speed is 140 kts. with A319/321 and modified A320 RATs stalling at less than 125 kts.
☂This speed limit is for electrical power and the RAT will continue to supply hydraulic power to much slower speeds.

✈SYSTEM ACCUMULATOR'S
☂An accumulator in each system helps to maintain a constant pressure by covering transient demands during normal operation.

☂Three system accumulators are pressurized with N2 to a pressure 
of 1950 psi.
☂The brake accumulator is pressurized to 1200 psi pressure.

✈PRIORITY VALVE 
☂Priority valves cut off hydraulic power to heavy load users if hydraulic pressure in a system gets low.

✈FIRE SHUTOFF VALVE'S
☂Each of the green and yellow systems has a fire shutoff valve in its line upstream of its engine-driven pump.
☂The flight crew can close it by pushing the ENG 1(2) FIRE pushbutton.

✈LEAK MEASUREMENTS VALVE'S
☂Each system has a leak measurement valve upstream of the primary flight controls.
☂These valves, which measure the leakage in each circuit, are closed by operation of the LEAKMEASUREMENT VALVES pushbutton switch on the maintenance panel.

✈Leakage limitation

✈FILTERS
☂Filters clean the hydraulic fluid as follows ☂HP filters on each system and on the reservoir filling system and the normal braking system
☂return line filters on each line
☂Case drain filters on engine pumps and the blue electric pump (which permit maintenance crew to monitor pump wear by inspecting the filters for the presence of metallic particles).

✈RESERVOIR PRESSURIZATION
☂Normally,  HP  bleed air from engine 1 pressurizes the hydraulic reservoirs automatically.
☂If the bleed air pressure is too low, the system takes bleed air pressure from the crossbleed duct.
☂The systems maintain a high enough pressure to prevent their pumps from cavitating.

✈OVERHEAD PANEL discussion
ENG 1 (2) PUMP pb
⛑On : - The pump pressurizes the system when the engine is running.
⛑OFF:- The pump is depressurized. The generation of hydraulic power stops.
⛑ FAULT lt :-This amber light comes on, and the  ECAM  caution appears, if :‐
☠The reservoir level is low
☠The reservoir overheats
☠The reservoir air pressure is low
☠The pump pressure is low (inhibited on the ground, when the engine is stopped).

☂This light goes out, when the crew selects OFF, except during an overheat. (The light stays on as long as the overheat lasts).

✈ BLUE ELEC PUMP pb (guarded) 
☂AUTO : If AC power is available, the electric pump operates :
⛑In flight‐On the ground
⛑if one engine is running or
⛑ if the crew has pressed the BLUE PUMP OVRD pushbutton on the maintenance panel.
☂OFF : The pump is de-energized.
☂FAULT lt : This amber light comes on, and a caution appears on the  ECAM.

✈NOTE- Same as green or blue pump in yellow

✈PTU PB SWITCH:-
⛑AUTO-The power transfer unit runs automatically when the differential pressure between the green and yellow systems is more than  500 PSI.
Note: OFF : The  PTU  is inhibited during the first engine start and automatically tested during the second engine start.
⛑OFF-Both the green and the yellow  PTU  electrohydraulic valves close. Power transfer stops
⛑FAULT- a this amber light comes on , when CAUTION appears on the ECAM.

✈RAT MAN ON pb
☂The flight crew may extend the  RAT  at any time by pressing the RAT MAN ON pushbutton.
☂Note: The  RAT  extends automatically if AC BUS 1 and AC BUS 2 are lost.

✈MAINTENANCE PANEL
☂BLUE PUMP OVRD pb sw (guarded)
⛑ON : The blue electric pump is on if the ELEC PUMP pushbutton switch on the  HYD  panel is at AUTO.
⛑Off : The blue electric pump is off.

☂LEAK MEASUREMENT VALVES pb sw (guarded)
⛑OFF: The corresponding electrohydraulic valve closes and shuts off hydraulic supply to the primary flight controls.
⛑On : The corresponding electrohydraulic valve opens to go back to normal hydraulic supply.

✈ECAM HYD PAGE

(1) Reservoir quantity- It is in green, unless the fluid level goes below the warning level, in which case it becomes amber
(2) Reservoir LO AIR PRESS-This appears in amber, and a caution appears on  ECAM, if the air pressure for the indicated reservoir drops below normal.

(3) Reservoir OVHT This appears in amber, and a caution appears on  ECAM, if the temperature of returning hydraulic fluid temperature at the inlet to its reservoir is above normal.
(4)FIRE VALVE
Cross line -Amber: The valve is fully closed.
In line - Green :The valve is not fully closed. (5)OVHT -This appears in amber if the electric pump for that system (blue or yellow) overheats.
(6)RAT
RAT  -White :- RAT is Stowed
RAT - Green :-RAT is not stowed
RAT  -Amber :Pressure for stowing the  RAT  has been applied, or the  RAT  pump is not available.
(7)ELEC -This legend, normally white, becomes amber if the associated power supply fails.
(8) YELLOW ELEC PUMP control
White : The electric pump is off.
Green : The electric pump is ON.
(9)PTU  control

1)⛑Green :PTU pushbutton switch is in AUTO and the  PTU  is not transferring pressure.
⛑Amber: The  PTU pb-sw  is OFF.
2)⛑Green : The  PTU  is supplying the green hydraulic system.
3)Green : The  PTU  is supplying the yellow hydraulic system.
(10) ENG PUMP control and low pressure indication
⛑In line (Green) : The pushbutton switch for the designated PUMP is on and hydraulic pressure is normal.
⛑Cross line (Amber) : The pushbutton switch for the designated PUMP is OFF.
⛑ “LO” (Amber) : The pushbutton switch for the designated PUMP is on and hydraulic pressure is LOW.

(11)SYSTEM LABEL-
⛑Pressure >1450psi - green or white
⛑pressure <1450psi - amber
(12) System pressure
(13) PUMP This legend, normally white, becomes amber when N2 is below idle.

✈HYD PTU : This memo appears in green, when the power transfer unit is running.

✈RAT OUT : This memo appears in green, if the Ram Air Turbine is not fully stowed. The color changes to amber during flight phases 1 and 2.

✈SAFETY PRECAUTIONS
☂make sure that you obey all the  AMM safety procedures.
☂ Make sure that the hydraulic system you work on is isolated before you pressurize the other hydraulic systems.
☂Make sure that the travel ranges of the flight controls are clear. (Movement can cause injury to persons and/or damage to the aircraft).

☂Do not get hydraulic fluid or hot gas from hydraulic reservoir on your body.(Use protective clothing to prevent risk of poisoning and burns.)
☂ Use solvents, cleaning agents, sealants and other special materials in a ventilated area.
☂ To prevent inadvertent breathing or contact with your body, use applicable gloves, eye protections and face mask.
☂Install safety devices and warning before working on or near landing gear and related doors.

✈HYD SYSTEM MAINTENANCE TYPE'S
☂Air in hydraulic system
☂Hydraulic reservoir servicing
☂Hydraulic fluid sampling
☂External leaks.

✈Dispatch with hydraulic leak

✈Necessary tools for hydraulic system

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