A magnetic ring of a permanent magnet is installed on the non-magnetic piston. When the magnetic ring moving with the piston approaches the Magnetic Switch Sensor Cylinder Npn, the two reeds of the tongue spring switch are magnetized to attract each other, and the contact is closed; When the magnetic ring moves away from the Magnetic Switch Sensor Cylinder Npn, the reed loses magnetism and the contact is disconnected. When the outlet point is closed or disconnected, it sends an electrical signal (or makes the electrical signal disappear), and controls the corresponding solenoid valve to complete the switching action. Magnetic Switch Sensor Cylinder Npn is generally equipped with an indicator light for switching action and an overvoltage protection circuit, which is encapsulated in a shell with resin.