Hydraulic & Pneumatic Systems Flashcards
What are the two basic types of hydraulic fluid that are used in a modern aircraft?
Mineral-based 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. If a break in the system should allow the main pump to pump all of its fluid overboard, there will 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 the 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 cease, the shear section will break, disconnect the pump from the engine and prevent further damage
What does an unloading valve do in a hydraulic system?
the unloading valve regulates the pressure in the hydraulic system. It does this by moving some of the fluid from the pressurized system back into the reservoir when the pressure is too high. This continues until the pressure drops to a certain level, at which point the pump resumes pushing fluid into the system to maintain 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 the purpose of an orifice check valve in an aircraft hydraulic system?
An orifice check valve allows full flow of fluid in one direction through the valve, but restricts the flow in the opposite direction.
Where are line-disconnect fittings normally located in an aircraft hydraulic system?
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.
What is the source of the compressed air that is used in a medium-pressure pneumatic system on a turbine-engine powered aircraft?
This air is normally bled from one of the stages of the engine compressor.
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. The moisture separators remove this water before it can freeze and block the system.
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. The valves act as a pump unloading valve.
Closed-center selector valves are installed in parallel with each other. They direct fluid under pressure to one side of the actuator, and fluid from the other side of the actuator to the system return manifold. In their off position, they trap fluid in the lines between the valve and the actuator.
