Operation characteristics of a frequency valve for hydraulic free-piston engines

To control the working frequency of a single piston hydraulic free-piston engine, the configuration and connection of a novel frequency valve were presented. The two steps in the process of opening and the closing action of the valve were investigated theoretically. The pressure test system for the valve dynamic characteristics was developed and the on-off characteristics were analyzed. The results indicate that the novel valve has operation characteristics that contain large flow area and high response. The large flow area is gained by a large diameter of the main spool. The higher response of the pilot valve and the large diameter of the secondary spool satisfy the high response requirement of the frequency valve. The time delay in the process of opening includes two parts which are the time delay between the output of the signal, and the time delay between the action of the pilot valve and the main valve.