Hydraulic and Pneumatic Systems Flashcards
(20 cards)
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 fluid through a bladder, a diaphragm, or a piston.
What are the two basic types of hydraulic fluid that are used in modern aircraft?
Mineral base fluid and phosphate ester base fluid.
What kind of filter is a micronic filter?
A filter with a special paper element.
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.
Where are line-disconnect fittings normally located in an aircraft hydraulic system?
Normally in the lines that connect the engine-driven pump to the aircraft hydraulic system.
What is meant by 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.
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 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 does an unloading valve do in a hydraulic system?
The unloading valve, or pressure regulator, controls system pressure by shifting the pump outlet fluid from the pressurized system back into the reservoir when the system pressure is high enough.
What kind of device is used to control the speed of movement of the piston in a pneumatic actuator?
A variable orifice.
Why do most high-pressure pneumatic systems include a moisture separator?
When the pressure of the stored air is reduced to the value that is needed in the system, the temperature drops enough to freeze any water that is in the air.
What is the difference between an open-center selector valve and a closed-center selector valve?
Open-center selector valves are installed in series with each other, and the hydraulic fluid flows through their center when no component is being actuated. Closed center selector valves are installed in parallel with each other.
What is used to flush a hydraulic system that uses Skydrol hydraulic fluid?
Trichlorethylene.
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 that is required for a particular aircraft?
In the maintenance manual for the aircraft. This information is also on a placard on the system reservoir.
What is used to remove phosphate-ester base hydraulic fluid from aircraft tires?
Soap and water.
What must be done to the lines that are disconnected when servicing an aircraft hydraulic system?
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 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.
Why do some hydraulic pressure gauges have a snubber installed between them and the hydraulic pump?
The snubber keeps the gauge from fluctuating.
