Question

Could you give me a worked example on how to determine pump head needed in piping system with branch?

Answer 1

Figure is an example from my “Branch Line Pumping Alternatives” spreadsheet. It allows a user or designer to compare a standard branch-line pumping system with several alternative designs and calculate the potential cost savings of those alternative designs. It is an evaluation tool—not a design tool.

In this example, a single pump at Point A supplies two branches at Points B and C. The system requires a pump that can provide 600 gallons per minute (gpm) at 200 feet of TDH. Point B is at an elevation of 100 feet and has an outflow of 400 gpm. Point C is 100 feet higher and has an outflow of 200 gpm. This is illustrated by the upper red, angled line. To meet these conditions, 43.2 horsepower (HP) is required.

An alternative to a single line with two branches is two separate lines supplied by individual pumps. These are illustrated by the two lower, angled, red lines. The first line delivers 400 gpm from Point A to Point B at a head of 100 feet and requires 14.4 HP. The second line delivers 200 gpm from Point A to Point C at a head of 200 feet and also requires 14.4 HP. The total HP for the two individual lines is just 66 percent of the single branch line, so significant electrical savings are available. Will the electrical savings make the two-line system cost effective?