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 its 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 a high altitude where there is not enough atmospheric pressure to do this.
What are 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. This information is also on a placard on the system reservoir.
What type of pump is a gear pump considered?
A gear pump is a constant displacement, high pressure pump.
What type of pump is a piston pump with a variable cam plate considered?
Fuel pumps may be divided into two distinct system categories: (1) constant displacement and (2) variable displacement. A piston pump with a variable cam changes the effective (not actual) length of each piston stroke. This makes this type of pump a variable displacement with constant pressure.
What is the purpose of an accumulator in an aircraft hydraulic system?
The accumulator holds pressure on the hydraulic fluid in the system. The pressure is held by compressed air or nitrogen acting on the fluid through a bladder, a diaphragm, or a piston.
What is a single-action hydraulic actuating cylinder?
A linear actuating cylinder that uses hydraulic fluid under pressure to move the piston in only one direction. The piston is returned by a spring.
What is the difference between a single-acting and double-acting hand pump?
Single-action pumps move fluid on only one direction of handle operation. Double-acting hand pumps move fluid on both directions of handle movement.
If a system requires a lower pressure than system pressure, what type of valve is used?
A pressure reducer valve.
What is used to remove phosphate-ester base hydraulic fluid from aircraft tires?
Soap and water.
How can you be sure that a replacement seal in a hydraulic component is compatible with the fluid used in the system?
Use only the seal identified by part number that is specified in the component maintenance manual.
What must be done to the lines that are disconnected when replacing an aircraft hydraulic system component?
They must be capped with the correct fluid line cap or plug. Masking tape or other types of adhesive tape should never be used.
What must be done before a pressurized reservoir is serviced?
All of the pressure must be bled off.
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.
