Flow Indicators

The most urgent and simplest question asked when a ventilation system is to be checked is, “Is the ventilation system on?” or “Is there any airflow passing through the system?” That the electric switch is on or that an operating lamp is shining docs nor always indicate that everything is alright. The airflow may, for many reasons, be reduced or stopped without any indication of malfunction. Nor is it always easy to determine whether the airflow rale from, e. g., an inlet air unit is as it is supposed to be. One common reason is that the unit is placed high above the floor, beyond the person’s reach. A simple, inexpensive, and effective method to arrange for hourly or continuous checking is to place some string or a strip of light material so that it will flutter distinctly. A cotton string, paper or plastic strip, or any other suitable mate­rial glued, screwed, firmly tied, or fixed with tape to some part in the inlet airflow will serve perfectly well. A change in how the flow indicator behaves will give rea­son for a more accurate check of the ventilation system. This technique has also been used for surface flow’visualization, especially for wind tunnel studies in the au­tomotive and the aircraft industry.8