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AGK Systems > AGK Systems - Hydraulic Systems > Flashcards

AGK Systems - Hydraulic Systems Flashcards

1
Q

What is a single acting actuator?

A

Hydraulic pressure moves the piston in one direction only.
A spring supplies return force.

In general, actuators convert hydraulic pressure into movement.

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2
Q

Double acting actuator.

A
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3
Q

What is a non return valve?

A

Acts as a one way valve.
Used to prevent back flow.
Fitted below or after pump to maintain flow direction.

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4
Q

What is a selector valve?

A

Allow the control input into a system and direct oil flow to a consumer.

Mechanical systems use manual selector valve.

Electrical systems use servo selector valve.

Some feature rotary selectors while others feature spool valve.

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5
Q

What is a servo control valve?

A

Controls the flow and direction of hydraulic fluid to an actuator.

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6
Q

What are the 2 fundamental types of system?

A

Passive and Active.

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7
Q

What is a passive system?

A

No hydraulic pump.
Stores energy to use later.
Power must be supplied by Pilot.

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8
Q

What is an active system?

A

Mechanically driven pump(s).

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9
Q

What is an open centre/low pressure circuit?

A

Operates at 2000psi.
Pressure is only generated when it is required.
Used on older light aircraft.
Can only operate one system at a time, effectively.
Uses a spur gear pump to provide power.

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10
Q

What is a closed centre system?

A

Maintains constant supply of hydraulic pressure.
Fluid is continuously pumped around the system.
Pressure flow remains low until a service selection is made.
Requires off loading valve to allow pump to unload.
-off load condition reduces engine power required.

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11
Q

Describe a light aircraft system.

A

May only have 1 active hydraulic circuit, for the landing gear.
Uses a self contained hydraulic power pack, operated by a reversible DC electric motor.
Flow and pressure control valves complete the system.
-Gear is held in the retracted position by the hydraulic lock.
-The pump comes online when required to restore system pressure.
-Gear is mechanically locked down then power to the pump is switched off.
-If the system fails, a dump valve breaks the hydraulic lock and allows the landing gear to gravity extend.

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12
Q

What is the hydraulic resivoir?

A

Stores hydraulic fluid sufficient for all actuators at full extension.
Normally pressurised but may be vented to atmosphere.
Has a sight glass: accumulators fully charged and components at correct setting.

Pneumatic pressurise it

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13
Q

What are accumulators?

A

Comprises pressurised gas and fluid in a cylinder separated by a piston or rubber diaphragm.
Pre charged with nitrogen.
When its all running, gas pressure = hydraulic pressure.

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14
Q

What are hydraulic pumps?
What types are there?

A

Usually driven from the accessory gearbox.

Engine driven
Electrical motor driven
Hand operated
Driven by RAT
Driven by PTU.

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15
Q

What is a constant delivery pump?

A

Typically spur gear system.
Flow rate dependant on speed of rotation of gears.
Requires ACOV.

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16
Q

What is an automatic cut off valve?

A

When pressure increase too high, a poppet valve opens to create an idling circuit.
Acts as a flow control valve, drains excess flow to reservoir and provides required flow for operation.
System leaks cause ACOV to operate excessively.

17
Q

Constant pressure pump.

A

Used on systems that operate +3000psi.
Pump comprises of a series of pistons in sleeves. Entire internal assembly rotates. A control piston adjust angle of swash plate and hence the output from the pump.
NO ACOV OR Accumulator necessary.

On start up: swash plate at a minimum deflection (0 degrees, upright), a blocking valve off loads the pump, recirculates oil inside the pump, pressure to suction.

Lubricated by hydraulic fluid.

18
Q

What are hydraulic motors?

A

Rotary actuator uses hydraulic pressure to generate rotary motion.
Hydraulic pressure forces down pistons in cylinder block.
Angle of swash plate translates linear piston movement into rotary movement.
Operating screw jacks to drive flap and slat mechanisms.
Also known as an axial piston motor or bent axis motor.

19
Q

What are hydraulic filters?

A

Keeps the fluid free of contamination (>10microns diameter).
Normally fitted downstream of the hydraulic pump.
If clogged, warning lights and bypass valve automatically allows unfiltered fluid to flow.

20
Q

What is a pressure relief valve?

A

Protects system from over pressurisation.
Excess pressure acts against sprig causing ball to unrest.
Fluid returns to reservoir.
The ball unseats at its cracking pressure.
Full flow relief valve - equivalent of total pump output.

21
Q

What is a restricter (choke) valve?

A

Reduces fluid flow to slow speed of operation of a service.

22
Q

What is a shuttle valve?

A

One service to be operated by 2 independent supplies.
Guarantees an adequate supply if one fails.
operates on differential pressure.

23
Q

What is a shut off valve?

A

Shut off services, similar to fuses.
Isn’t self regulating but is operated by an external controller, pilot.

24
Q

What is a hydraulic fuse?

A

Prevents sudden loss of hydraulic pressure.

25
Q

What requirements do large aircraft hydraulic systems have?

A

redundancy
reactive
multiple services simultaneously
emergency sources of pressure
greater output for big loads

Most systems operate under 3000psi
Large aircraft about 5000psi

26
Q

Describe large aircraft hydraulic system.

A

Uses a closed system, pressure always available.
Different circuits have different colours.
Seperate engine driven pumps supply each system
PTUs are fitted to cater for pressure loss in a system.
RAT provides emergency power after pump failiure.

27
Q

RAT.

A

Typically pressurizes blue system: flight controls, flaps.
Auto deployment when electrical power is lost at AC buses 1 and 2.

28
Q

Hydraulic PTU.

A

Used on large aircraft when more than 1 hydraulic system is employed.
Uses a hydraulic motor driven by the live system to provide hydraulic pressure to the dead side.

29
Q

Purpose of pop out indicators.

A

Warn of impending by pass situation.

30
Q

What is caviation?

A

Air bubbles.
This is why hydraulic revisor is pressurised.

31
Q

Where does a vapour lock occur?

A

Fuel system

AGK Systems (13 decks)

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