Abstract: The idea and classification of 7c bridge with three hydraulic resistance are offered. The property of the π bridge is studied. A new principle pilot relief valve with π bridge pilot hydraulic resistance is put forward, the theoretical analysis and experiment shows that the static pressure of the pilot relief valve may be increase or keep constant or decrease in terms of different pilot resistance value when the relief quantity of the valve increase.

Key words: Hydraulic resistance π bridge network, Performance, Relief valve