These are known as orifice-type check valves, or damping valves. Fluid enters the valve through the inlet port, flows around the lower part of the piston and exits the outlet port, where it flows to the primary first unit to be operated. Pneumatic Power System Maintenance Maintenance of the pneumatic power system consists of servicing, troubleshooting, removal, and installation of components, and operational testing. If the pressure drops below 2,200 psi, the priority valve closes and no fluid pressure flows to the noncritical systems. The leakage is returned to the system through a case drain port. For the most part, hydraulic systems are simple, safe and economical because they use fewer moving parts compared to mechanical and electrical systems, which makes them easier to maintain.
A person trying to work on these different machines would have to know each brand's ins and outs. High-Pressure Systems For high-pressure systems, air is usually stored in metal bottles at pressures ranging from 1,000 to 3,000 psi, depending on the particular system. Thus, at pump outlet pressures above 2,850 psi, pump displacement decreases as outlet pressure rises. Notice that the hydraulic power unit is dedicated to this machine. Two main advantages of air-operated circuits are their low initial cost and design simplicity. This heat is transferred to the fluid and, in turn, to the packing rings, causing them to deteriorate rapidly.
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. A few other manufacturers are setting up central power units when the plant has numerous machines that use hydraulics. You don't need to use a compressor because its uses fluid it needs a pump. The inline filter assembly is comprised of three basic units: head assembly, bowl, and element. Skydrol® does not appreciably affect common aircraft metals—aluminum, silver, zinc, magnesium, cadmium, iron, stainless steel, bronze, chromium, and others—as long as the fluids are kept free of contamination. Most selector valves are mechanically controlled by a lever or electrically controlled by solenoid or servo. The liquid usually becomes darker in color, higher in viscosity, and acids are formed.
Some of the more common gasket materials are asbestos, copper, cork, and rubber. If otherwise noted, the cartridge is to be considered contaminated with moisture and should be replaced. As the piston moves toward the right, it pushes return fluid out of the right-hand chamber and through the selector valve to the reservoir. They reduce weight by eliminating hydraulic lines and large quantities of hydraulic fluid. Another -- called a counterbalance valve -- located in the rod end line of the main cylinder keeps it from running away when the directional control valve shifts.
However, that creates another precision problem; high-pressure pneumatic cylinders are essentially two-state systems; the piston or actuator is typically at one or the other of its extremes of movement, and transitions between them very quickly as gas pressure is applied to one side or other of the cylinder. The vane-type power pump is also a constant-displacement pump. Engine bleed air is also used to pressurize the reservoirs of the hydraulic system. But in many applications oscillations like that would cause system failure. If an excessive amount of foreign matter, particularly oil, is exhausted from any one system, the lines and components should be removed and cleaned or replaced.
Check Valve Another common flow control valve in aircraft hydraulic systems is the check valve. Since the constant-delivery pump provides a fixed quantity of fluid during each revolution of the pump, the quantity of fluid delivered per minute depends upon pump rotations per minute. New fluids have extremely good properties over a wide temperature range and offer excellent fire-resistance, and since the fluid is constantly circulating in a filtered, closed, airless system, thermal and contamination management is straightforward and effective. Conversely, the landing gear must be completely retracted before the doors close. Reservoirs can be serviced by pouring fluid directly into the reservoir through a filler strainer finger strainer assembly incorporated within the filler well to strain out impurities as the fluid enters the reservoir. Spherical The spherical-type accumulator is constructed in two halves that are fastened and threaded, or welded, together.
Once depleted, the bottles must be recharged by maintenance personnel. Such valves are installed in the pressure and suction lines of the system immediately upstream and downstream of the power pump. When gaskets, seals, and hoses are replaced, positive identification should be made to ensure that they are made of the appropriate material. Rotary actuators are not limited to the 90° pivot arc typical of cylinders; they can achieve arc lengths of 180°, 360°, or even 720° or more, depending on the configuration. Pressure relief valves are adjusted by increasing or decreasing the tension on the spring to determine the pressure required to open the valve. Since most aircraft applications require instantaneous operation, closed-center systems are the most widely used.
Directional control valves The circuit in Figure 5-2 has only one to extend and retract the main cylinder. Liebherr supplies the full range of aircraft pneumatic systems, and Bonleux says the reliability of its equipment has increased many-fold in the past few decades. The micron element is designed to prevent the passage of solids greater than 10 microns 0. As soon as small amounts of sludge or other deposits are formed, the rate of formation generally increases more rapidly. Nitrogen from the bottles is released by actuation of an outlet valve.
The pressure builds up in the system to overcome the resistance and moves the piston of the actuating cylinder; fluid from the opposite end of the actuator returns to the selector valve and flows back to the reservoir. The hydraulic case drain fluid that lubricates and cools the pumps return to the reservoir through a heat exchanger. They deliver a fixed quantity of fluid per revolution, regardless of the pressure demands. The reservoir pressurization module supplies airplane bleed air to the reservoirs. As the pockets between the gears on the left side of the pump move from a lowermost position toward a topmost position, the pockets increase in size, resulting in the production of a partial vacuum within these pockets. A high flash point is desirable for hydraulic liquids because it indicates good resistance to combustion and a low degree of evaporation at normal temperatures. Oil from the right cylinder goes to tank.