Operational checks

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Applying hydraulic power

Aviation Structural Mechanic

Model HCT-10 Stationary Hydraulic Test Stand

OPERATIONAL CHECKS. When operating the test stand, you need to periodically check the condition of system fluid through the sight glass. If you see evidence of air, bleed the system at both the test stand and air bleed points in the aircraft until the fluid appears clear. Also, you need to monitor the filter differential pressure indicators, particularly those associated with the 3-micron filter assemblies. In some cases, loaded filter indicators may extend due to cold starting conditions. Reset the indicator and continue to monitor it until the equipment reaches the normal operating temperature. If a loaded filter is indicated, shut down the equipment and return it to the supporting activity. Another condition that would require you to return the equipment to the supporting activity is if the fault indicators light; in this case, shut down the unit and return it to the supporting activity. In case of an emergency (for example, a ruptured hydraulic hose in aircraft), you should open the bypass valve to relieve pressure and stop the flow of hydraulic fluid to the aircraft. Pay attention to warning signs such as a sudden drop in engine oil pressure or any unusual engine noise. If any engine part fails, Stop the engine immediately.

SHUTDOWN PROCEDURE. In aircraft equipped with pressurized reservoirs, hydraulic accumulators, or surge dampers, a reverse flow of fluid through the aircraft filters could damage the system. You need to use the correct shutdown procedures. When you have finished the required aircraft tests, leave the bypass valve in the closed position. Reduce the volume setting to zero and adjust the pressure compensator to minimum. Allow several minutes for stored pressure in the aircraft to bleed off, via normal internal leakage. On stands equipped with a pressure and return line shutoff valve, close the valve instead of reducing the volume and pressure compensator.

Slowly open the pressure bypass valve. Let the engine run at 1,000 rpm for about 5 minutes (engine-driven models only), then push the throttle down completely. Place the panel light switch in the OFF position. Remove the external hoses from the aircraft hose ports. Connect one end to the hose storage manifold diconnects on the test stand. Do not drag the hose ends on the deck or expose them to contamination. Install all dust caps and plugs, including those at the aircraft quick disconnects. Close all the access doors to protect instruments and controls.

MULTISYSTEM OPERATION. When per-forming troubleshooting, rigging, and specific tests on dual flight control systems that have tandem actuators, you often need to apply SE hydraulic pressure to two or three systems in an aircraft at the same time. Simultaneous, multisystem operation involves using separate hydraulic test stands for each system, or by manifolding two or more systems to a common test stand that has a sufficient flow capability. Less equipment is needed with the latter method, but it has several limitations that you should know.

If you use a single test stand and manifold, hydraulic fluid between the connected systems is exchanged. If the fluid in one system is contaminated with particulate matter smaller than 3 microns, cross-contamination of the other system(s) will occur. Using a single test stand may not satisfy differing flow and back pressure requirements of the multiple systems to be powered. Depleting or overfilling aircraft reservoirs might result. If a single test stand is used, high transient flow demands in one system could adversely affect the performance of the other systems. Total isolation between systems could possibly degrade critical flight control system performance tests. The use of jury-rigged manifolds not specifically engineered for the purpose is a safety hazard to personnel and a possible source of system contamination. Properly designed hydraulic manifolds can be used in limited, specific applications to power multiple hydraulic systems to form a common hydraulic test stand. This configuration must be evaluated by the cognizant engineering activity to make sure it is acceptable and that its use is strictly limited to that particular application. All approved manifold use must be directed in the applicable aircraft MIM, and complete information on the source of the required hardware must be provided. Do not use manifolds that are not authorized.