# Water Column

Published: December 31, 2017 | Last updated: July 5, 2023

## What Does Water Column Mean?

Water column is an alternative way of expressing measurements of pressure. This measurement is defined as the pressure produced by a 1-inch by 1-inch column of water with a specified height. For example, if the pressure on a surface is equal to 2 inches of water, this means that the pressure on it is equivalent to a square-inch (1in2) column of water with a height of 2 inches.

The density (or unit weight) of water is 0.036 pounds per cubic inch. Therefore, the pressure of 1 inch of water in a water column is 0.036 psi or 1/28 psi. In other words, a column of water 28-inches high will produce a pressure equivalent to 1 psi.

Water columns are useful for quantifying low pressures. For example, instead of expressing a pressure as 0.072psi, it may be more convenient, in some applications, to express this same pressure as 2-inches of water.

## Trenchlesspedia Explains Water Column

Another way of defining water column is the amount of pressure it takes to raise a 1-inch x 1-inch column of water by 1 inch. This unit of pressure measurement is ideal for equipment with low operating pressures, like vapor recovery systems. Water column is also best suited for expressing minute pressure differentials across pipelines and shafts.

Early water column measurements were taken using relatively simple devices known as manometers (water tubes). However, modern instruments, such as dials or digital gauges, are frequently used.

### How Is the Concept of Water Column Used in the Trenchless Industry?

The pressure exerted by a water column is used in the installation of cured-in-place piping (CIPP) liners. The pipe liners are first vacuum impregnated with a specified resin that allows it to stick to the pipe's inner surface. The liner is then inverted (turned inside out) into the host pipe using the hydrostatic pressure created by a water column.

In addition to unrolling and inverting the resin-impregnated liner, the water column's pressure presses the liner against the walls of the pipe. This ensures that there is proper bond between the pipe and the resin. This pressing action also ensures that the resin is forced into cracks, joints, and other irregularities.

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