Optimization of a Fast Switching Valve for Big Flow Rates

In this paper the optimization of a fast switching valve regarding the critiria rubustness to flow forces and low cost under the constraints of a nominal flow rate of at least 40 l/min and a switching time of about 1ms is presented. Basis for the optimization process was a concept of a switching valve which was derived from three previous designs, all of which had also been prototyped. The main difficulties that have to be overcome are. (i) Spool sticking problems, if tiny land structures are applied, (ii) flow forces which are substantially disturbing the spool motion, (iii) flow oscillations generated by fast switching which create unpleasant noise and pressure pulsation. Problem (i) can be avoided by a specific spool and land design which stabilizes the centered spool position. Flow force reduction can be achieved by shape modification of the spool and the grooves in the sleeve but may conflict with problem (i). The faster the valve the smaller the parasitic hydraulic inductivities of the interior flow channels of the valve have to be. Avoiding such problems gives decisive design constraints in which the optimization problem has to be embedded. Optimization parameters have been spool diameter, spool stroke, and inertia. Flow forces could be reduced considerably by a CFD analysis of different designs of land structures. The resulting design was realized as a new prototype which fulfills the demands on switching time and flow rate. Furthermore, the design is simple which promises a cheap production.