Pressure difference switches are installed at both ends of the air filter to monitor the pressure difference. When the filter becomes blocked and the pressure difference exceeds a certain threshold, the pressure difference switches will close, triggering an alarm signal. This is done to prevent the filter from becoming excessively dirty, which could lead to a decrease in air quality, equipment malfunction, or jeopardize the safe operation of the equipment. Pressure difference protection devices are also installed in air compressor oil filters and oil fine separators.