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AHT-63 Control Panel Controls and InstrumentsContinued
MULTISYSTEM OPERATION

Aviation Structural Mechanic (H&S) 3&2 - How airplanes are built and how to maintain them
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see an indication of a loaded filter after the fluid reaches normal operating temperature (85°F minimum), shut down the test stand and have replacement filter elements installed. On test stands that have a fluid sight glass and manual air bleed valve, periodically operate the valve and monitor the sight glass throughout the cleaning cycle to eliminate visible indications of entrapped air. When recirculation cleaning and deaeration are complete, analyze the hydraulic fluid for contamin- nation Terminate the fluid flow to the external service hoses in preparation for connecting them to the aircraft. Disconnect the service hoses from manifold assembly and reinstall the manifold dust covers. APPLYING HYDRAULIC POWER.— Before you connect a test stand to an aircraft system, make sure that all personnel, workstands, and other ground-handling equipment are clear of flight control surfaces, movable doors, and other units. Stay clear of these areas when either electric power or hydraulic pressure is applied to the aircraft. Sudden movement can cause injury or damage. NOTE: Refer to the applicable maintenance manual for the specific procedures to follow when applying external electric and hydraulic power. Before connecting the hydraulic test stand to the aircraft, set the test stand controls to the positions and values required to accomplish the aircraft tests. Operate the test stand to confirm the settings. Reduce the volume adjustment to minimum flow and shut down the stand. Connect the test service hoses to the aircraft ground power quick-disconnects, making sure that all connectors are clean before connection. Mate all the attached dust caps and plugs to protect against their contamination during test stand operation. Do not kink or damage test stand hoses when connecting them to aircraft systems. Keep the hoses uniformly bent while bending around structures or equipment. Maintain and follow the recommended minimum inside bend radii. A 1/2-inch pressure hose should have a 2.30-inch radius, a 5/8-inch pressure hose a 5.37-inch radius, and a 1-inch hose a 5.90-inch radius. Before you can apply hydraulic power, you need to check the aircraft reservoir level. Fill it to the level specified in the applicable MIM or MRC. If necessary, service the reservoir using an approved fluid service unit. Then, set up the test stand for either aircraft or test stand reservoir operation, as specified in the applicable MIM. You can set the required mode of operation by using the reservoir selector valve on stands that have this equipment, or use the reservoir fluid supply valve. When the test stand reservoir supply valve is closed, the aircraft reservoir will operate. The test stand reservoir is preferred because the vented reservoir allows aircraft fluid deaeration during system operation (fig. 4-15). Use this mode whenever practical. When a test stand is equipped with return line, back pressure reducing valves, test stand reservoir operation can be used even in situations where the aircraft reservoir is normally used. Adjust the back pressure reducing valve by presetting the value equivalent to normal aircraft reservoir pressure. Make sure that the aircraft controls are in the specified ground check positions required for obtaining normal reservoir fluid level. Apply external hydraulic power and trim the back pressure reducing valve until a stable, proper fluid level is obtained in the aircraft reservoir. Periodically check the fluid level. Ensure back pressure reducing valve is set properly or the aircraft may be damaged by overpressurization. After you have adjusted the back pressure reducing valve, you can start the test stand, and allow Figure 4-15.—Test stand operating modes. 4-34







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