1993-04-01

Dissolved Gas - The Hidden Saboteur 931404

Almost all hydraulic power components, to properly perform their tasks, rely upon one basic, physical property, i.e., the incompressibility of the working fluid. Unfortunately, a frequently overlooked fluid property which frustrates this requirement is its ability to absorb, i.e., dissolve, store and give off gas. The gas is, most often but not always, air. This property is a complex one because it is a function not only of the fluid’s chemical make-up but temperature, pressure, exposed area, depth and time. In its relationship to aircraft landing-gear, where energy is absorbed hydraulically, this multi-faceted fluid property can be detrimental in two ways: dynamically, i e., loss of energy absorption ability and statically, i.e., improper aircraft attitude on the ground. The purpose of this paper is to bring an awareness to this property by presenting: 1) examples of these manifestations with some empirical and practical solutions to them, 2) illustrations of this normally ‘hidden sabotcur’ at work, 3) Henry’s Dissolved Gas Law, 4) room-temperature. saturated values of dissolved gas for a number of different working fluids, 5) a description of the instrument used to obtain them, 6) some ‘missing elements’ of the Dissolved Gas Law pertaining to absorption, 7) how static & dynamic conditions effect gas absorption and 8) some recommended solutions to prevent becoming a victim of this ‘hidden saboteur’.

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