When a hydraulic system is worked on, cleanliness is No. 1. Dirt and metal particles can score valves, seize pumps, clog orifices, resulting in major repair work.

Oil and Filter Changes

Despite all the precautions you take when working on the hydraulic system, some contaminates will get into the system anyway. Good hydraulic oils will hold contaminates in suspension and the filters will collect them as oil passes through. A good hydraulic oil contains additives that work to keep contaminants from damaging or plugging the system. However, these additives lose their effectiveness after an extended period of time; therefore, oil changes at the recommended intervals can ensure that contamination is held to a minimum. By changing the oil at its recommended interval ensures that the additives will do their job.

Regular filter changes ensure solid particles are removed from the system. They should be changed more often under adverse operating conditions. When filters are changed, thoroughly clean the filter housing before installing a new filter. Remember to add enough fluid to compensate for any fluid lost in filter replacement.

Cleaning and Flushing the System

Cleaning and flushing the system should be performed based on the manufacturer's recommendation or when the system is known to be contaminated. The nature and amount of deposits in a particular system may vary widely. Inspection of the system may show any condition between a sticky, oily film and a hard, solid deposit (gum or lacquer formation) which completely chokes off the system. If the system is drained periodically according to the manufacturer's recommendations, the formation of gum and lacquer will be greatly reduced.

If there is no gum or lacquer formation suspected, clean the system as follows:

1. Drain the system completely.

2. After draining, clean any sediment from the reservoir, and replace the filter elements.

If flushing is required because the oil is badly contaminated, clean and flush the system as follows:

1. Drain the system completely.

2. Refill the system with the recommended hydraulic oil for the system involved.

3. Operate the equipment to cycle the flushing oil through the system. Ensure that all valves are operated so that the new oil goes through the lines.

NOTE

The time necessary to clean the system will vary, depending on the condition of the equipment. Usually from 4 to 48 hours is sufficient for most systems.

(Drain out the flushing oil, replace the filters, and refill the system with clean hydraulic oil of the recommended type.)

If gums or lacquer has formed on working parts and the parts are sticking, remove the affected parts and clean them thoroughly. Consult the manufacturer's manual before removing and cleaning any parts for proper procedures.

Preventing Leaks

Leaking hydraulic connections are frequent reasons for maintenance. Some leaks are external, being evident on the outside of components. Others are internal, which does not result in actual loss of oil, but it does reduce the efficiency of the system.

INTERNAL LEAKAGE. - A small amount of internal leakage is allowed to provide lubrication of moving parts. This leakage is normal and does not result in faulty operation. On the other hand, an excess of internal leakage results in slow operation, loss of power, and overheating of the hydraulic fluid. The cylinders may creep or drift and, if the leak is bad enough, the control valves may not function properly.

Internal leaks are caused by wear of the seals and mating parts during normal operation. Leakage is accelerated by using oil that has too low a viscosity because the oil thins faster at higher temperatures. High pressures also force more oil out of leaking points in the system. This is why excessive pressures can actually reduce the efficiency of the hydraulic system.

Internal leaks are hard to detect. Usually, all you can do is observe the operation of the system for signs of sluggishness, creeping, and drifting. When these signs appear, it is time to test the system and pinpoint the problem.

EXTERNAL LEAKAGE. - External leaks not only look bad but make it hazardous for the operators of the equipment. A leak that allows floor plates to become slippery may cause the operator to fall on or off the