Hydraulic and Pneumatic Systems Flashcards
What kind of filter is a micronic filter?
A filter with a special paper element.
What is a double-action pump?
A pump that delivers fluid with the movement of the pump handle in both directions.
Why do most engine-driven hydraulic pumps have a shear section in their drive couplings?
If the pump should seize, the shear section will break, disconnecting the pump from the engine and preventing further damage.
What are the two basic types of hydraulic fluid used in modern aircraft?
Mineral-base fluid and Phosphate-ester base fluid.
Does the main hydraulic pump take its fluid from the bottom of the reservoir, or from a standpipe?
The main pump normally takes it fluid from a standpipe, while the emergency pump takes its fluid from the bottom of the reservoir. (If a break in the system should allow the main pump to pump all of its fluid overboard, there will still be enough fluid in the reservoir to allow the emergency system to extend the landing gear and actuate the brakes.)
Why are some hydraulic reservoirs pressurized?
Pressurization ensures that fluid will be supplied to the inlet of the pumps at high altitude where there is not enough atmospheric pressure to do this.
What are the two ways aircraft hydraulic reservoirs may be pressurized?
By an aspirator in the fluid return line or by bleed air from one of the engine compressors.
What is used to flush a hydraulic system that uses Skydrol hydraulic fluid?
Trichlorethylene or the solvent recommended by the aircraft manufacturer.
What is used to flush a hydraulic system that uses mineral base hydraulic fluid?
Naphtha, Varsol, or Stoddard Solvent.
Where can you find the type of hydraulic fluid required for a particular aircraft?
In the maintenance manual for the aircraft or on a placard on the system reservoir.
What type of pump is a gear pump considered?
A gear pump is a constant displacement pump, high pressure pump.
What type of pump is a piston pump with a variable cam plate considered?
A piston pump with a variable cam changes the effective (not actual) length of each piston stroke. This makes this pump a variable displacement with constant pressure.
What system fault could cause an accumulator pre-charge pressure to increase?
A leaking seal in the accumulator that allows fluid to pass into the air side of the accumulator.
What is the first step when checking hydraulic reservoir fluid level?
Verify that the hydraulic systems are set to the configuration specified in the maintenance manual. (For example: landing gear down, gear doors retracted, parking brake off, thrust reversers retracted, and pressure accumulators set to the correct pressures.)
What is the most likely cause of hydraulic fluid flowing through a filter bypass valve?
The filter has become clogged.
