Natural air, after being filtered and purified by an air filter, enters the air pump. The air is compressed by the air pump to generate pressure and then rapidly flows into the air chamber through the check valve. The gas diffuses in two directions, one to the pressure sensor in the pressure control unit and the other to the underwater vent pipe. When the air pump stops working, the check valve closes and the underwater vent pipe opening is sealed by the gas. Thus, a closed cavity connecting the pressure sensor and the underwater ventilation pipe opening is formed.

According to the theory of gas molecular dynamics, it is known that the pressure at all points in a closed gas container is equal. The pressure at the bottom of the gas pipe is equal to the pressure at the sensor of the pressure control unit. By subtracting the maximum pressure from this pressure, the net pressure of water can be obtained. Through a series of conversions and corrections, the measured water level can be derived