Abstract: The non-circular opening spool valve is one of basic construction of hydraulic valve, which places axisymmetrically several notches on the spool to form the restriction configuration. This type of valve is widely used in direction and velocity control for hydraulic actuators. Its restriction location, shape and flowing angle are shifted with the spool motion, and therefore it is difficult to achieve a reasonable prediction of the flow force by the traditional theoretic methods. The computational fluid dynamic method is used to investigate the three dimensional flowing fluid in a typical flow-direction control valve. The numerical result of the steady flow force and flow-pressure characteristics on the whole opening range agree well with the observed one. The results show that direction of steady flow force in the non-circular opening spool valve changes with the shift of the flow direction on the notch pass. A very useful guidance on the prediction of the steady flow force and other performances of non-circular opening spool valve is provided.

Key words: Fluid simulation, Non-circular opening spool valve, Steady flow force