| Hydraulic systems troubleshooting varies according to | | | | replacement of relief valves, actuators, and other |
| the complexity of the system and the components in | | | | units, including tubing and hoses. Care should be |
| the system. It is, therefore, important that the | | | | exercised to prevent system contamination damage |
| technician refer to the troubleshooting information | | | | to seals, packings, and other parts, and to apply |
| furnished by the manufacturer. | | | | proper torque in connecting fittings. When installing |
| (1) Relief valves repair... lack of pressure in a system | | | | hydraulic fittings, valves, etc. always lubricate the |
| can be caused by a sheared pump shaft, defective | | | | threads with hydraulic fluid. |
| relief valves needing repair, regional aircraft control | | | | Overhaul of hydraulic and pneumatic units is usually |
| valves, the pressure regulators, unloading valves | | | | accomplished in approved repair facilities; however, |
| stuck in the "kicked-out" position, lack of fluid in the | | | | replacement of seals and packings may be done |
| system, the check valves installed backward, or any | | | | from time to time by technicians in the field. When a |
| condition that permits free flow back to the | | | | unit is disassembled, all O-ring and Chevron seals |
| reservoirs or overboard. If a system operates | | | | should be removed and replaced with new seals. The |
| satisfactorily with a ground test unit but not with the | | | | new seals must be of the same material as the |
| system pump, the hydraulic pumps should be | | | | original and must carry the correct manufacturer's |
| examined. | | | | part number. No seal should be installed unless it is |
| (2) If a system fails to hold pressure in the pressure | | | | positively identified as the correct part and the shelf |
| section, the likely cause is the pressure regulator, an | | | | life has not expired. |
| unloading valve, leaking relief valves nedding repair, or | | | | When installing seals, care should be exercised to |
| a leaking check valve. | | | | ensure that the seal is not scratched, cut, or |
| (3) If the pump fails to keep pressure up during | | | | otherwise damaged. When it is necessary to install a |
| operation of the subsystem, the pump may be worn | | | | seal over sharp edges, the edges must be covered |
| or one of the pressure-control units may be leaking. | | | | with shim stock, plastic sheet, or electrical tape. |
| (4) High pressure in a system may be caused by a | | | | The replacement of hydraulic units and tubing usually |
| defective or improperly-adjusted pressure regulator, | | | | involves the spillage of some hydraulic fluid. Care |
| an unloading valve, or by an obstruction in a line or | | | | should be taken to ensure that the spillage of fluid is |
| control unit. | | | | kept to a minimum by closing valves, if available, and |
| (5) Unusual noise in a hydraulic system, such as | | | | by plugging lines immediately after they are |
| banging and chattering, may be caused by air or | | | | disconnected. All openings in hydraulic systems should |
| contamination in the system. Such noises can also be | | | | be capped or plugged to prevent contamination of |
| caused by a faulty pressure regulator, another | | | | the system. |
| pressure-control unit, or a lack of proper accumulator | | | | The importance of the proper torque applied to all |
| action. | | | | nuts and fittings in a system cannot be |
| Aviation component repair. | | | | over-emphasized. Too much torque will damage metal |
| Commuter aircraft hydraulics overhaul, maintenance | | | | and seals, and too little torque will result in leaks and |
| of hydraulic system components, involves a number | | | | loose parts. The proper torque wrenches with the |
| of standard practices together with specialized | | | | appropriate range should be used in assembling |
| procedures set forth by manufacturers such as the | | | | system units. |