What is the principle of the pilot solenoid valve?

When the power is turned on, the electromagnetic force opens the pilot hole, and the pressure in the upper chamber drops rapidly. A pressure difference of up, down and high is formed around the closing member. The fluid pressure pushes the closing member upward, and the valve opens. When the power is off, the spring force closes the pilot hole The inlet pressure quickly passes through the bypass hole to form a low-to-high pressure difference around the valve closing member, and the fluid pressure pushes the closing member to move downward to close the valve.