the hydraulic liquid, the hydraulic system must be flushed.

NOTE: The presence of foreign particles in the hydraulic system indicates a possible component malfunction that you should correct before flushing the system.

A hydraulic system in which the liquid is con- taminated should be flushed according to current applicable technical instructions. Flushing procedures are normally recommended by the manufacturer. The procedure varies with different hydraulic systems. One method is as follows:

Drain out as much of the contaminated liquid as possible. Drain valves are provided in some systems for this purpose; while on other systems, lines and fittings must be disconnected at the low points of the system to remove any trapped fluid in the lines and components. Close all the connections and till the system with the applicable flushing medium. Any of the hydraulic liquids approved for use in power-transmission systems may be used for flushing purposes.

CAUTION Diesel fuel oil must not be used for flushing hydraulic systems in active service, because of its poor lubricating qualities and its contaminating effect on the subsequent till of hydraulic liquid.

While being flushed with an approved hydraulic liquid, power-transmission systems can be operated at full load to raise the temperature of the liquid. Immediately following the warming operation, the system should be drained by opening all drain outlets and disconnecting the hydraulic lines to remove as much of the flushing medium as possible. All filter elements, screens, and chambers should be cleaned with new fluid before filling the system with the required service liquid.

CAUTION The system should not be operated while or after draining the liquid.

Power-transmission systems and their intercon- nected hydraulic controls whose inner surfaces have been inactivated and treated with a corrosion prevention or preservation compound must be flushed to remove the compound. The latest current instructions for flushing and other operations required to reactivate a particular system must be strictly followed to prevent damage.

Some hydraulic systems are flushed by forcing new liquid into the system under pressure, forcing out the contaminated or decomposed liquid.

Hydraulic liquid which has been contaminated by continuous use in hydraulic equipment or has been expanded as a flushing medium must not be used again but should be discarded according to the prevailing instructions.

CAUTION Never permit high-pressure air to be in direct contact with petroleum base liquids in a closed system, because of the danger of ignition. If gas pressure is needed in a closed system, nitrogen or some other inert gas should be used.

REFERENCES

Aviation Hydraulics Manual, NAVAIR 01-1A-17, Commander, Naval Air Systems Command, Washington, D.C., 1989.

Aviation Support Equipment Technician, Naval Education and Training Program Management Support Activity, Pensacola, Fla., 1990.

Base Vehicle Equipment Mechanic, Extension Course Institute, Air University, Gunter Air Force Station, Montgomery, Ala., 1986.

Fluid Power, Naval Education and Training Program Management Support Activity, Pensacola, Fla., 1990.