Computational Fluid Dynamics Investigation of Flow through Pneumatic Control Valve

Low-cost on-off pneumatic directional control valves are widely used with digital control circuits to control the position or the speed of pneumatic actuators. These valves have a limited flow capacity that hinders the system fast response. Therefore, deeper understanding of the internal air flow through the valve and its interaction with valve geometry will allow further performance improvement according to the required application. In this paper, a Computational Fluid Dynamics (CFD) model for a low-cost internal pilot, electrically operated pneumatic 3/2 directional control valve has been developed to investigate the effect of the valve's geometry on the valve's outlet flow rate. The flow behaviour and the critical flow areas have been discussed. The computational model has been validated by comparing the predicted results by published experimental results in addition to results obtained by an analytical simplified model. The results have shown that improving the valve geometry by rounding the sharp edges of the valve at the critical flow areas would led to an increase of the valve's outlet mass flow rate. At the same inlet pressure ranging from 2 to 12 bar, the mass flow rate increase was 79.1% at pressure 2 bar and 103.6% at 12 bar. This could increase the pneumatic actuator response and enhance the accuracy of the position control in pneumatic circuits that uses modified low-cost valves.