Explanations: Hydraulic and Pneumatic Power Systems Flashcards
What is a selector valve?
A fluid power system component that directs the flow of pressurized fluid to one end of an actuating cylinder, and simultaneously, directs return fluid to the reservoir from the other end of the cylinder.
A closed center selector valve has a variety of ports. Whether a given port is an input or output port depends upon the configuration of the valve’s interior which rotates into different positions, either closing off or providing a path for fluid to flow either into or out of a given port.
what is the difference between a pneumatic system and a hydraulic system?
Pneumatics provides fluid power by means of pressurized air or gases. Hydraulics provides fluid power by means of pressurized liquids, such as oil or water
What is a compressor in a pneumatic system?
A machine that takes ambient air from the surroundings and discharges it at a higher pressure.
What is the difference in installation between a close center and open center selector valve?
Open center selector valves are installed in series with each other, while close center valves are installed in parallel with each other.
Why are relief valves installed?
to protect a system from excessive pressure buildup that can be caused by thermal expansion or by a compressor power system malfunction.
Why does an aircraft pneumatic system require a moisture separator?
Because if moisture were allowed to remain in the air, the temperature drop that occurs when the air expands would cause it to freeze and block the system.
What type of components require bleeding of the fluid to remove the air and what type only require the operation of several cycles to remove the air?
The cycles remove air from double-acting hydraulic components, whereas bleeding the fluid removes air from single-acting components such as brakes.
What does a pressure regulator in a hydraulic system do?
It maintains a system operating pressure within a predetermined range. The regulator unloads the pump when the upper limit of this pressure is reached.
The pump remains unloaded, circulating the fluid through the system with no opposition until the lower limit of the pressure is reached, at which time the pump again forces fluid into the system.
What is the difference between and gasket and a packing?
a gasket is not subject to motion, and a packing is.
What role does the backup ring perform in a high pressure system?
It prevents the fluid from forcing the o-ring into the space between the piston and cylinder wall.
Can an accumulator be removed from an aircraft with an air preload still in it?
Yes, but the preload must be discharged before the accumulator itself is disassembled.
Why have synthetic fluids been developed?
because of the flammability of petroleum base fluids.
Why is skydrol adversely affected by atmospheric humidity?
it is susceptible to contamination from moisture.
What is a flash point?
The lowest temperature at which there will be enough flammable vapor to support combustion when an ignition source is applied.
What number is skydrol?
MIL-H-8446
Systems using skydrol should be flushed with what? Components using skydrol should be flushed with what?
systems flushed with trichloroethylene. components with stoddard solvent, MEK, or isopropyl alcohol.
What two systems is a shuttle valve connected to in a landing gear actuating cylinder?
both the normal operating system and the emergency system, but it can’t access both at the same time.
Why should you always adjust pressure regulating valves with the highest pressure setting first?
If a valve having a lower pressure setting is adjusted first, you will never be able to reach the pressure required for the higher setting.
What is the issue caused by a low accumulator preload?
the accumulator is not holding the pressure on the system as long as it would if the preload pressure were correct.
What is another name for an unloading valve?
a system pressure regulator.
How does a unloading valve, aka system pressure regulator, work?
When the system pressure reaches the regulating range, a check valve in the unloading valve traps pressure in the system where it is held by the accumulator.
A valve then opens to allow fluid from the pump to circulate back to the reservoir with very little opposition.
The fluid flows with the pump unloaded until the system pressure drops to the kick-in pressure of the unloading valve. When the kick-in pressure is reached, the output of the pump is again directed into the system.
If all pressure relief devices fail, what occurs?
the shaft will shear and prevent the pump being further damaged?
What is the hydraulic pump drive shaft?
Hydraulic Pump - Gear category consists essentially of two intermeshing toothed gears enclosed in a common housing. A shaft, the drive shaft, extends beyond the housing. This shaft is attached to one of the gears which, when it is turned by the shaft, drives the second gear.
Where are thermal relief valves installed?
In portions of a hydraulic system that normally hold fluid trapped by a selector valve. They relieve the pressure that is built up in the lines as the fluid is heated by the surrounding air.
Thermal relief valves are set to relieve a pressure higher than any of the other valves, so they will not interfere with normal system operation of protection.
