Abstract: Nonmagnetic hydraulic motor servo system requires that servo valve must stay far away from non-magnetic motor since the servo valve will produce electromagnetic interference which can-t be ignored. In order to analyze the long pipe-s influence on the nonmagnetic hydraulic servo system, a mathematical model of valvecontrolled motor servo system based on precise pipe model was developed and simulated. The research results reveal the law of pipe length, pipe diameter and other related parameters affecting on the system and show that long pipe effects will reduce the hydraulic natural frequency and hydraulic damping by a large margin. The experiments verify the above conclusions, and show that threeloop feedback control strategy instead of traditional simple proportionalintegralderivative (PID) control strategy can lower the adverse impacts owing to long pipe to some extent.  

Key words: nonmagnetic surrounding, long pipe, threeloop feedback