Internal leakage in the main stage of servovalves: An analytical and CFD analysis

The internal leakage in two stage servovalves causes unwanted power consumption; it is the sum of two contributions: the internal leakage in the main stage and the internal leakage in the pilot stage. While the latter can be assumed almost constant regardless of the spool position, the former is maximum at null and decreases with increasing opening degree of a given valve. Because of this, the power consumption is significant when a valve is at rest, namely, when it is not modulating flow. Despite being a very important feature of these valves, the internal leakage occurring in the main stage around null and its associated issues are not properly addressed in the scientific literature. Because of this, this paper aims at providing a deep investigation into this phenomenon. In particular, it will be discussed how it can be studied using analytical equations. In addition, a CFD analysis is carried out in this paper in order to obtain a simple CFD model that has general validity and that can be used to predict the internal leakage around null in the main stage. The developed model can be easily reproduced by manufacturers, and it can be used to understand the effects of geometrical imperfections and tolerances as well as fluid properties upon the internal leakage around null. The present paper has been realized in collaboration with Moog controls ltd, a world leading manufacturer of servovalves.