Flashcards
M11 Hydraulics
Cards in this deck (33)
- 14 main things hydraulic systems are used for?- Landing gear
- Brakes
- Cargo doors
- Flight controls - 2Basic unit for pressure?Pascals - (1 newton per square metre)
(pressure = force/area) - 3Psi and Bar?Pressure measured in psi in aviation.
1 Bar = 14.5 psi - 42 types of Hydraulic pressure?Hydrostatic - (static fluids)
Hydrodynamic - (dynamic fluids) - 5Two types of hydraulic fluid?- Synthetic (VIOLET) eg. skydrol + hyjet
- Mineral (RED)
You can mix mineral/mineral oils and synthetic/synthetic oils but not synthetic/mineral (no cross mix) - 6Requirements of hydraulic fluids?- Low flammability
- Good lubricating quality
- Resistance to freezing
- Non evaporating
- Non foaming
- Chemically stable
- Non Hygroscopic (ability to take in water) - 7what "packing" solutions resolve leaking problems?Seals such as O rings, Quard rings and T rings for example depending on their jobs. As well as back up rings for extra strength.
Seals - rubber
Backup rings - teflon - 8Working with Seals.Different seals can be damaged by working with the wrong hydraulic fluids. - may swell in size. (check manual/part number).
Also consider temperatures and force that may act on them. - 9Static and Dynamic Seals.Static seals - seal against pulsating pressure
Dynamic seals - seal against stroking/rotational movements. - 10Basic Cycle of hydraulics.Storage (reservoir) ---->
System pressurisation ---->
User distribution (eg. flight control) ---->
Storage (reservoir)
and repeat. - 11The distribution system comprises of what?The manifold.
- 12How does the shape of the reservoir assist the system?Sealed and cylindrical. The shape resists change in pressure due to altitude and temperature. Sealed to permit pressurisation by air.
- 13Purpose of the reservoir?compensate for variations in the need for hydraulic fluid caused by the operation of hydraulic components.
keep a reserve of hydraulic fluid in case there is a fluid leak in the system
(There is enough fluid in the reservoir to compensate for all users in the system) - 14What is the purpose of horizontal sheet metal in the reservoir?Act as Baffles to allow positive fluid feed to the pumps when the aircraft is in rapid deceleration/rough turning movement.
- 15Components of the reservoir?-Quantity transmitter (float or capacitor)
- Low level switch (indicates to cockpit)
- Quantity gauge (pointer or sight glass)
- Drain valve (at bottom to empty reservoir)
- Air manifold (to pressurise reservoir) - 16Purpose of pressurising the reservoir?- Air pressure in tank Is low at high altitudes so not enough fluid can get to pumps.
pressurising prevents:
- Foaming
- Evaporation
- Cavitation - 172 ways of pressurising the reservoir?- Hydraulic pressure. (uses a piston to create a pressure to stabilise the reservoir)
- Air pressure. (most common pressurisation, done by engine, but if engine fails - done by pneumatic system. Pressure reduced to 50psi.) - 18Components in the reservoir pressurisation manifold?This manifold is to pressurise air in the reservoir by receiving this air from engines or pneumatic systems).
consists of:
- check valve
- filter (with differential pressure indicator)
- pressure reducing valve
- fluid separator fitted with a drain valve and a ground connector - 19RestrictorAt the supply line from engine (not on the manifold).
purpose to reduce the flow of air passing through the pipe. (controlled by check valves)
eg. a flapper type check valve will shut off if pressure in the reservoir is greater than the supply) - 20How is pressure reduced from the engine pressure in the manifold?pressure reducing valve regulates this. High pressure air acts against a bellows mechanism (normally held open by spring). If air pressure is too high, the bellows close. As it closes, a valve is forced into a new position by another bellows and spring mechanism. This closes the aperture and this prevents air getting in and reduces pressure of the air going out (maintains it at 50psi).
- 21Function of a water separator?air goes through; cleanable element which separates water, then through a disk with holes In it to prevent blockages. Water then collects in a container and air continues out the outlet.
Note: air supplied by pneumatic system will not need this as this air is generally "dry" - 22Purpose of the ground connector valve in the reservoir?allows the reservoir to be pressurised by ground equipment by the use of a nitrogen bottle.
- 23Reservoir Air Manifoldafter the pressurisation manifold air enters the reservoir air manifold. This joins together the components which control reservoir air pressure. Consists of; check valve, pressure switch, pressure relief valve and a pressure indicator.
- 24Overpressure in reservoir air manifoldIn the case of over-pressurisation the pressure relief valve protects the system by a spring loaded cone that is pushed back due to pressure in order to release the high pressure to ambient air. The air pressure switch (low pressure switch) detects this and sends low pressure signals to cockpit.
- 25Depressurisation valves in the reservoir.Each reservoir has one.
- needed to depressurise for servicing/changing of components.
- spring and piston assembly
- piston normally prevents pressurised air escaping. but when spring is activated and cap is rotated... the piston rises and pressurised air escapes. - 26what is an Accumulator?A device where potential energy is stored in form of a compressed gas or spring, or by a raised weight used to exert a force against a relatively incompressible fluid. used to accumulate energy and to smooth out pulsations.
- 27Why is a smaller pump needed when an accumulator is in the system?because it stores energy from the pump in low demand periods. This energy can be instantly used on demand at a faster rate than the pump.
- 28How does an accumulator act as surge/pulsation absorbers?They can cushion hydraulic hammer, reducing shocks from rapid operation or sudden starting/stopping of power cylinders in a hydraulic circuit (i.e hydraulic pumps).
- 294 types of accumulator- weight loaded piston type. (uncommon)
- spring type. (uncommon)
- diaphragm (bladder) type.
- hydro-pneumatic piston type. (use nitrogen as spring cushion with hydraulic fluid; they are separated by thin diaphragm or piston) - 30Compressibility of hydraulic fluid?Hydro-pneumatic accumulator; compresses 1.7% under 5000psi.
if 2% of fluid is released out of the system the pressure drops to 0. This then gives a quick response for power demand with no delay due to incompressibility.
However, the gas in this hydro-pneumatic can be compressed to high pressure and low volumes in order for this energy to be stored ready for use. - 31Purpose of gas cushioning?The driven member of the hydraulic system stops suddenly and sends a pressure wave back through the system. This shock wave creates pressure a lot higher than normal pressures and can lead to failure or objectionable noise. The gas cushion in an accumulator will minimize this shock.
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- Flashcards on M11 Hydraulics, created by Aiden Grocock on 31/10/2017.
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- Aiden Grocock
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