Automatic nitrogen pressure maintaining device of pure water tank

An automatic nitrogen pressure maintaining device of a pure water tank comprises a PLC (programmable logic controller), a touch screen, an air pressure sensor, a gas flow meter and a gas circuit electromagnetic valve, the output end of the air pressure sensor is connected with the input end of the PLC, the PLC is connected with the touch screen, three nitrogen input gas paths are arranged and connected to the pure water tank, the three nitrogen input gas paths are provided with a first gas path electromagnetic valve, a second gas path electromagnetic valve, a third gas path electromagnetic valve and a third gas path electromagnetic valve respectively, and the output end of the PLC 1 is connected with the first gas path electromagnetic valve, the second gas path electromagnetic valve and the third gas path electromagnetic valve respectively. The three nitrogen input gas paths are parallel graded flow gas paths, and each graded flow gas path is connected with a gas flow meter in series, so that positive pressur