Hydrostatic transmissions - Circuit assembly and design

As with most technologies, experience with hydrostatic transmissions enables us to identify and master a number of recurring problems.

Dealing with these problems calls on general mechanical concepts such as vibration, acoustics, lubrication, pollution and metallurgy.

The specificity of these problems in hydrostatic transmissions stems from the orders of magnitude involved, both in terms of fluid stresses and the tribological aspects of friction parts.

For example, the expansion flow of a fluid at a pressure of 300 bar generates velocities of the order of 250 m/s. A hydrostatic or hydrodynamic skid with an average height of 3 µm, between two parts in relative motion of 15 m/s, generates a shear (velocity gradient) of 5 × 10 ⁶ Hz. Such values are not encountered in classical mechanics.

It is therefore necessary, by returning to the elementary methods of analyzing physical phenomena, to identify a few predominant mechanisms in order, if possible, to control them.