The piston type steam solenoid valve is a step-by-step direct pilot solenoid valve, which can be divided into normally closed solenoid valves and normally open solenoid valves according to the different open and closed states when the power is cut off. Normally closed solenoid valve, after the coil is energized, the armature first drives the auxiliary valve plug to lift under the action of electromagnetic force. The fluid on the main valve cup flows away through the auxiliary valve, reducing the pressure acting on the main valve cup. When the pressure on the main valve cup decreases to a certain value, the armature drives the main valve cup and uses the pressure difference to open the main valve cup, allowing the medium to flow. After the coil is powered off, the electromagnetic force disappears and the armature falls back to its original position due to its own weight. At the same time, relying on the pressure of the medium, the main and auxiliary valves can be tightly closed.

A piston type normally open solenoid valve, after the coil is energized, due to the suction force, the moving iron core moves downward, presses down the auxiliary valve plug, closes the auxiliary valve, and the pressure inside the main valve cup increases. When the pressure rises to a certain value, the pressure difference between the upper and lower parts of the main valve cup is the same. Due to the electromagnetic force, the moving iron core loses the lower part of the main valve cup, compresses the main valve seat, and the valve closes. When the coil is powered off, the electromagnetic suction force is zero. The auxiliary valve plug and supporting iron core are lifted upward due to the spring action, and the auxiliary valve opens. The fluid on the main valve cup flows away through the auxiliary valve, reducing the pressure acting on the main valve cup. When the pressure on the main valve cup decreases to a certain value, the pressure difference is used to push up the main valve cup, and the main valve opens, allowing the medium to flow.