Yuchai pressure sensor signal is to use the pressure of the spring to adjust and control the pressure of the hydraulic oil. When the pressure of hydraulic oil is less than the pressure required for work, the spool is pressed by the spring in the inlet of hydraulic oil, the greater the pressure of hydraulic oil, the higher the spool is pushed up by hydraulic oil. Electromagnetic relief valve is a kind of hydraulic control valve, which mainly plays the role of constant pressure relief and safety protection in hydraulic equipment.