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31 Cards in this Set
- Front
- Back
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Why might hydraulic actuation be preferred to pneumatic or electrical systems? |
It provides smoother, steadier movement and has a high power to weight ratio. |
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What are the ideal properties of hydraulic fluids? |
They should be as incompressible as possible with a low viscosity, free flowing over a wide temperature range and have a high flash point. They should be chemically stable and not be effected by other components within a system. They must not foam when subjected to sudden pressure changes and have good lubrication properties. They must not form sludge. |
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What are the three types of hydraulic fluids used? |
Mineral based, vegetable based, synthetic ester based |
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What colour is mineral based hydraulic fluids, what seals are used, and how is it flushed? |
Red. Synthetic rubber seals. Flushed with naphtha, varsol or stoddard |
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What colour is vegetable based hydraulic fluid? And what seals are used? How is it flushed? |
Golden. Natural rubber seals. Flushed out with alcohol |
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What colour is synthetic ester based hydraulic fluid? and what seals are used? How is it flushed? |
Purple (skydrol). Butyl, ethylene propelene or Teflon seals. (Works over a higher temperature range). If it turns dark amber it has been overstressed. Flushed with MEK, isopropol alcohol or trichloroethylene |
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How can hydraulic pipes be identified? |
Blue and yellow label with the word hydraulics, symbol black circles |
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What problems may be present in fluid based systems? |
Aeration, external leakage, internal leakage |
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Where are gaskets used? |
Between non moving parts |
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Where are packings used? |
Between moving parts |
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Name the different types of one way seal |
Chevron, V shape and U shape (very high pressure) |
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Name the types of two way seals |
Bonded seals, o-rings, wiper rings (used where a positive seal and long life are required) |
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What are the basic components of a hydraulic system? |
Reservoir (pressurised or unpressurised), pump (EDP, EMDP, handpump, air turbine driven pump, EHP, PTU, APU, HYRAT), selector valve (rotary, linear, solenoid operated), actuator (rotary, linear) |
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Hydraulic systems can be split into two groups, what are they? |
Self idling, non self idling |
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What extra component is required in a non self idling system? |
An unloading valve |
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What is the function of a hydraulic Reservoir? |
To store fluid, provide a means for return fluid, allows for thermal expansion, supplies fluid to normal and emergency systems, filters water out of the fluid |
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Filter units catch particles or debris. What filtration range do these filters normally fall within? |
Between 5 to 10 microns |
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What role do accumulators carry out? |
Dampen out oscillations caused by the pump, ensure an immediate response to demand, store energy as a back up in case of pump failure, accommodate fluid volume changes due to thermal expansion |
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Name three types of accumulators |
Piston type, bladder, diaphragm (spherical types) |
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How is hydraulic fluid cooled? |
When it reaches a high enough temperature, it goes through a heat exchanger where fuel is used as a cooling medium |
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What is the purpose of a hydraulic pump? |
To provide a flow of fluid not create pressure, pressure is a biproduct of creating the flow. Pressure is a measure of the difference between pressure on either side of a valve |
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Name different types of constant volume, fixed displacement pumps for non self idling systems. |
Spur gear, gerotor, radial, vane (high volume, low pressure), fixed piston (lower volume, higher pressure) |
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Name the types of constant pressure, variable displacement pumps for self idling systems |
Stratopower (rotating swash plate set at a fixed angle. Fluid displacement varied by a control piston attached to spider), variable displacement piston (displacement varies with respect to the angle of the yoke. Low volume high pressure) |
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What role do electric motor driven pumps play? |
They back up the EDP when system pressure demand flow and pressure is high and also to supply hydraulic power in case of EDP failure |
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What alternative pressure generation systems are there? |
Duplication of supply, EMDP, air turbine motor driven pumps, power transfer unit, ram air turbines, hand pumps (mainly for maintenance) |
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Name three types of linear actuator |
Single acting(spring one end, fluid other end, actuated by hydraulic pressure, returned by spring pressure), double acting ( fluid both ends of the actuator, used in undercarriage systems), balanced (piston rod both ends). |
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Name two methods of rotary actuation |
Rack and pinion, and pump/motor |
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Name types of pressure control valves |
Pressure relief valve (open at 3450 psi, close at 2650psi), pressure regulator valve, thermal relief valve, pressure reducing valve |
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Name types of flow control valves |
Non return valve, restrictor valve, selector valve, sequence valve, hydraulic fuses |
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Where may you expect to come across a rack and pinion system? |
Nose wheel steering or windscreen wipers |
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Where may you expect a blow back valve to operate? |
In the flap system to protect against overstress should the flaps be in the wrong position with respect to the flight phase |
