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AGK Systems ATPL > Chapter 5 - Hydraulic Systems > Flashcards

Chapter 5 - Hydraulic Systems Flashcards

1
Q

4 Main Components of a Hydraulic System?

A
  • Reservoir
  • Actuator
  • Pump
  • Selector
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2
Q

What are the 2 types of Pumps?

A
  • Constant Pressure

- Spur Gear

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3
Q

Constant Pressure Pump

A

Swash-plate or cam-plater, operated by a control piston.

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4
Q

Spur Gear Pump

A

Output pressure depends on RPM.

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5
Q

(RAT) Ram Air Turbine

A
  • Deploys with electrical failure.
  • Generates electricity for critical parts.
  • Has external hydraulic pump.
  • Blades pitch based on RPM.
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6
Q

Power Transfer Unit (PTU)

A
  • Uses Hydraulic Motor to drive Hydraulic Pump on another system.

There is no transfer of fluid from one system to another.

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7
Q

How does a Air Turbine Motor work?

A
  • High pressure bleed air from the engine, power the air turbine.
  • This powers the Hydraulic Pump.
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8
Q

Actuators

A

Turn Hydraulic Pressure in to movement.
3 Types of linear actuators:

  • Single Acting Actuator
  • Double Acting un-balanced Actuator
  • Double Acting Balanced Actuator
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9
Q

Single Acting Actuators?

A
  • Piston moves in one direction.
  • A Spring supplies the return force.
  • Normally used as a locking device.

(Used on landing gear locking and unlocking mechanism).

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10
Q

Double Acting Un-balanced Actuator?

A
  • Moves in both directions.
  • Even with equal pressure applied the piston will move in one direction.
  • This is because one face has a smaller area due to the Actuating Rod.

(Flaps, Spoilers, Landing Gear)

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11
Q

Double Acting Balanced Actuator?

A
  • Moves in both directions.
  • Piston area on both sides is equal.
  • A given hydraulic pressure give an equal force on either side of the piston face.
    (Ailerons, Elevators, Yaw, Nose Wheel Steering)
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12
Q

Non-Return Valve (Check Valves) NRV

A
  • Allows fluid to only move in one direction.
  • Ball with spring attached, can only move one way.

Will have a marker on it indicating which way the flow goes (Helpful to maintenance).

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13
Q

Selector Valves

A
  • Direct the hydraulic fluid to the various parts of the system.
  • Operated Mechanically or Electronically.
  • Values can hydraulically lock the position of an actuator.

Can be ‘Rotary’ or ‘Slide Type’ (Linear).

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14
Q

Hydraulic Pumps are driven by?

A

Engine - Can be an issue if the engine is running at low RPM.

Electric Motor

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15
Q

Name given to the Pipes which deliver fluid to the components (Hydraulics)

A

Pressure Lines.

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16
Q

Name of the Pipes returning the non-pressurised Hydraulic Fluid?

A

Return Lines

Passed through a heat exchanger first to cool down the fluid.

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17
Q

Passive Hydraulic System?

A

No Hydraulic Pump.
All the power to move the flow is done by the pilot.

E.g. Foot brake in a car.

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18
Q

Active Hydraulic System?

A
  • Uses one of more Hydraulic Pumps

- Used on larger aircraft.

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19
Q

Open Centre Hydraulic Systems?

A
  • Used on aircrafts that don’t have large amounts of hydraulics power available.
  • Operates the landing gear, or the flaps. BUT NOT BOTH AT THE SAME TIME.
  • Only one system can be used at a time.
  • Uses a Spur Gear Pump to provide power.
20
Q

Off-Loading Valve?

A

Allows the pump to unload when services are not being operated.

  • Reduces the engine power required to drive it and also reduces the wear on the pump.
21
Q

Closed Centre Hydraulic System?

A
  • Maintains a constant supply of hydraulic pressure using a variable volume pump.
  • Services are in parallel which allow them to be used at the same time.
22
Q

Hydraulic Motor?

A
  • Uses hydraulic pressure to generate rotary motion.
  • Useful for operating screw jacks to drive the flap and slats mechanism.
  • The speed of the motor is dependant on the fluid flow rate.
  • Turns hydraulic pressure in rotary motion.

Allows both flaps to deploy symmetrically.

23
Q

Constant Delivery (Fixed Volume) Pumps?

A
  • Provides constant fluid supply, using a spur gear system.
  • 2 gears bring in fluid and propel it around the outside of the gears.
  • Requires Automatic Cutout valve (ACOV) Normally fitted in conjunction to regulate pressure.

Downstream of pressure filter and parallel with Non-return valve.

24
Q

Hydraulic Filter

A
  • Keeps the fluid free of contaminants.
  • Fitted downstream of the pump.
  • Traps particles larger than 25 microns. When blocked goes through the relief valve.

Diff pressure sensor operates warning light in cockpit
Or a red filter pop-put button protrudes from the main casing.

25
Q

If Hydraulic Filter becomes blocked…

A
  • A differential pressure sensor operates a warning light in the cockpit.
  • Or a red filter pop-out button protrudes from the main casing.
  • A bypass valve automatically allows unfiltered fluid to flow directly through the head.
26
Q

Priority Valve (Pressure Maintaining Valve)

A
  • Ensure sufficient fluid flow at all times to the primary control and wheel brakes.
  • Closes and isolates non-essential circuits if system pressure drops.
27
Q

Pressure Relief Valve (Pressure & Thermal)

A
  • Protects the system from over pressurisation.
  • A full flow relief valve (FFRV) can relieve the equivalent of total pump output.
  • May also act as a Thermal Relief Valve (TRV).
  • Directs excess pressure back into the reservoir.
28
Q

Restrictor Valve (Choke Valve)

A
  • Reduces the fluid flow to slow the speed of operation of a service.
  • A one-way restrictor allows full flow in one direct and restricted flow in the other.
  • The restrictor is normally used for SLOWING Landing Gear or Flaps extensions.
29
Q

Shuttle Valve (Hydraulics)

A
  • Allows one service to be operated by two independent supplies.
  • Guarantees an adequate supply if either system fails.
  • Under normal operating conditions the shuffle is to the left side.
  • When the main supply fails the shuttle moves to the right and allow the emergency supply to take over.
30
Q

Hydraulic Fuse?

A
  • Upstream of components.
  • Shuts off flow to prevent major fluid loss in a leak.
  • If the pressure becomes too great, then the pressure will drop behind the piston, forcing it to close.
  • Blocks everything downstream from it.
  • Everything upstream can continue to operate as before.
31
Q

Shut-off Valve? (Hydraulics)

A
  • Similar to hydraulic fuses. (They can shut off hydraulic flow)
  • However, the valve isn’t self regulating.
  • It is controlled by the cockpit.
32
Q

Automatic Cut-out Valve? (Hydraulics)

A
  • ACOVs are fitted in conjunction with a volume pump to regulate pressure.
  • When a large amount of pressure is present it forces a poppet valve to open.
  • When open it creates an ‘Idling Circuit’ which dumps excess pressure (Kicked out).
  • If there is a leak the AVOC will operate for longer.
33
Q 
Constant Pressure (Variable Volume) Pumps? (Hydraulics)
PISTON
A
  • Delivers 3000psi on demand.
  • Does not require an ACOV.

Features

  • Output volume NOT dependant upon pump RPM
  • Volume CAN be Altered - By altering swash plate (Stroke Length).
  • Self regulates and only supplies fluid needed to maintain constant working pressure.
  • Engine Driven.
  • On start-up: Pump swash plate is at a max deflection.
  • Pump is lubricated by hydraulic fluid.
34
Q

Hydraulic Pumps may be: (Types of pumps)

A

Engine Driven Pumps (EDP) - Driven by accessory gearbox.

  • Electric - Used during emergency’s .
  • Hand pump
  • RAT (Ram Air Turbine)
  • Driven by an hydraulic motor, or Power Transfer Unit (PTU)

Piston Pumps are used in larger aircraft.

35
Q

Hammering? (Hydraulics)

A

Incorrect pre-charge pressure can lead to hammering in the Automatic Cutout Valve (ACOV), this is detrimental to the efficient system operation.
- Usually caused by a leak in the system.

36
Q

The job of an Accumulator? (Hydraulics)

A
  • Store fluid under pressure.
  • Provide a limited supply of pressurised fluid in an emergency.
  • Dampen pressure fluctuations in the system.
  • Allow for thermal expansion.
  • Allow for small internal leaks
37
Q

Accumulators?

A

Piston in a sealed cylinder.

  • The piston provides a tight seal between the fluid and gas (Nitrogen).
  • If the pump fails, the Nitrogen pushes the hydraulic fluid in the cylinder out, allowing for emergency hydraulic pressure.

Used on the Landing gears front nose steering.
Allows up to 6 independent brake applications.

38
Q

De-Aerator Tray

A

Fluid drops on to a ‘De-aerator tray’ which removes the air bubbles from the fluid. (In reservoir)

39
Q

‘Fins’ and ‘Baffles’ job?

A

Inside the Reservoir to prevent swirling of fluid due to aircraft manoeuvring.

40
Q

Purpose of the ‘Stack/Stand Pipe’?

A

To give emergency supply out of the reservoir in case of a major fluid loss.

  • Manually operated by hand or emergency pump.
41
Q

Why is the Reservoir Pressurised?

A
  • Prevents the fluid from boiling at high altitude.
  • Provides a positive pressure at the inlet to the Engine Driven Pumps (Prevents Cavitation).

Pressurised via Engine Bleed air.
A relief valve prevents over pressurisation.

42
Q

What is a Hydraulic Power Pack?

A

Uses Reversible DC Electric Motor
- Used in an emergency to break the hydraulic lock and allow the landing gear to be lowered on lighter aircraft.

Supply switches on and off depending on when it is needed.

43
Q

What is a ‘Hydraulic Reservoir’?

A
  • Stores the Hydraulic Fluid.
  • Normally pressurised by Engine Bleed Air. (Can have vents)
  • Allows for thermal expansion, and accepts returning low pressure fluid.
  • Holds an excess of fluid incase of leak.
  • Content can be checked through sight glass window (Or in cockpit via Temp + Quantity gauge).
  • When maintaining checks should be done when the accumulators are fully charged.
  • Ram displacement fluid is also taken into account.
44
Q

Loss of hydraulic system pressure in one system will be shown by?

A
  • A master caution,
  • An amber light
  • Loss of pressure reading for the affected system.
45
Q

What could be the cause of temperature rising?

  • No loss of quantity visible.
  • No loss of pressure.
A

Internal leak.
Hydraulic fluid squeezing through a gap in the system and warming the pipes up.
Conducted to the fluid.

46
Q

Hand Pump use?

A

Used for maintenance or emergency backup on a light AC.

DOUBLE ACTING.

AGK Systems ATPL (8 decks)

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