What does a gas pressure reading of 4 inches wc indicate on a U-Tube manometer?

A gas pressure reading of 4 inches of water column (wc) indicates that there is a difference in pressure between the two sides of the U-Tube manometer. In this case, a reading of 4 inches wc functions as a measurement of the pressure exerted by the gas against the column of water, showing that one side experiences a higher pressure than the other.

When the pressure is greater on one side, it pushes the water column down on that side and elevates it on the opposite side. The measurement of 4 inches wc implies that the water level is indeed 4 inches lower on the side with higher gas pressure and consequently 4 inches higher on the side with lower pressure. Therefore, the difference in the height of the water column indicates the level variation that results from this pressure difference.

In this scenario, the answer accurately reflects that the water level is 2 inches lower on one side and 2 inches higher on the other side, which cumulatively results in a 4-inch difference. This not only illustrates the fundamental principle of how a U-Tube manometer works but also demonstrates how to interpret the pressure readings in a practical context, especially when dealing with gas pressure systems.