Determination of the dynamic flow characteristics of an electro-hydraulic servo-valve using a laser velocimeter

The dynamic flow characteristics of an electro-hydraulic servo-valve have been determined experimentally using a laser velocimeter. The volume flow rates were predicted from centre-line velocity measurements using a finite difference digital computer analysis of the Navier-Stokes equation adapted for incompressible flow along a tube. The analysis was first verified at low pulsatile system excitation frequencies by making velocity measurements at radial positions across the flow tube and comparing the profile thus generated with that from the computer analysis. The results show that the attenuation in flow amplitude with increasing frequency could not be accounted for by inertia effects alone and could be explained by changes in the contraction coefficient of the valve spool orifice. An expression is given for the change in flow amplitude as a function of the valve non-dimensional inertial loading.