Description of a U-tube manometer

A manometer is an instrument that has a small tube in the shape of a U that is filled with liquid to measure pressure or flow. A U-tube manometer is used as an indicator that the fan on the mitigation system is working. This image shows two U-tube manometers. The first with the liquid levels in the U-tube equal on both sides, indicating that the fan on the mitigation system is not working properly. The other U-tube manometer shows the liquid levels on either side of the u- tube are different in height (h), indicating a pressure difference(P1,P2), which confirms that the system is working properly.