Servo Valve Internal Leakage as Affected by Contamination

Servo valves are rejected in the field for internal leakage rates which exceed specification requirements during specified maintenance inspection. Some assemblies are near this specification limit, which poses the problem of whether to replace the unit or wait until the next specified inspection period. The purpose of this investigation was to determine the rate of increase in internal leakage under simulated field conditions, and this rate of increase could then be used to determine remaining life expectancy of the servo valve. A definite correlation for internal leakage was established between contaminated fluid from tactical sites as balanced against less contaminated fluid directly from new one-gallon cans.

The presentation lists the material and equipment used during the test procedure, and discussion and conclusions. Internal leakage versus time curves for both fluids are illustrated. These curves show that the maximum useful life of a servo valve can be increased with hydraulic fluid which has a higher degree of control in the level of contamination.