Technical Service Center — Water Conveyance Group
Pipelines—Pressure PipesDiameter is one way to describe a pipe. Another way is by how much pressure or head the pipeline resists without bursting. Engineers measure water conveyance pipeline's heads in pounds per square inch (p.s.i.) or feet (of water). This is equivalent of saying that a pipeline can hold the pressure caused by a column of water so many feet high.
If the pipeline conveys water that is not under pressure and is not flowing full, then it is called a "free flow" pipeline.