How is ventilating pressure measured by the water gauge?

Ventilating pressure is measured by the water gauge primarily through the difference in elevation of two water columns. This method involves using a U-shaped tube partially filled with water, where one side is exposed to the atmospheric pressure, and the other side is connected to the mine ventilation system. When a pressure differential exists due to airflow, it causes a change in the water levels in each side of the tube.

The height difference between the two columns of water indicates the magnitude of the pressure, thus providing an effective measure of the ventilating pressure. This method is particularly useful in mining operations as it is a straightforward and reliable way to assess airflow and ensure that proper ventilation standards are maintained for safety.

Other options mentioned do not contribute directly to measuring ventilating pressure. Temperature changes influence air density but do not provide a direct measure of pressure. Flow rates relate to the volume of air but not the pressure differential itself. Observing atmospheric conditions may give general insights but does not accurately reflect the specific ventilating pressures within a mine.