Investigation into the characteristics of full-bridge spiral pilot stage

A new high reliable hydraulic pilot stage named full-bridge spiral pilot stage (FBSPS) is proposed in this paper. It utilize a spiral groove on a round pilot spool and two stream holes on the pilot piston form a pair of differential variable orifice, it series with two upstream fixed orifice on the cylinder wall from a full-bridge hydraulic resistance bridge which can utilize for hydraulic pilot servo valve. The structure and geometry model are described. And the mathematical model is carried out. The design parameters are optimized by simulation. A prototype is carried out based on the simulation. Both simulation and experiment results indicate that the static and dynamic performance FBSPS is satisfy to develop high performance servo valve. The gain of pressure sensitive is very large and the rising time of step response is less than 3ms. Moreover, the FBSPS shows some advantages such as high resistance to oil contamination and large flow rate capability than traditional nozzle flapper pilot stage.