Understanding Swimming Pool Piping and Water Velocity

One of the most difficult things we run across in our business each day is dealing with improperly sized equipment and piping. It is not uncommon for us to show up on a service call to find the pump is not sized correctly for the job or the piping is undersized. One of the common complaints is that the pump is loud. When we inspect and test the system what we find is that most of the time the noise is not the pump rather the sound of the water moving through the pipes at higher then recommended velocity.

We do our best to help clients understand that in these situations thier are really only two solutions. One is getting a new pump and the other is replumbing the pool. In most cases we find replacing the pump with a Pentair Inelliflo solves the problems in a more cost effective manner. As a general rule the Association of Pool and Spa Professionals (APSP) recommends that suction side piping should not exceed 6 feet per second on the suction (vacuum) side of the system or 8 feet per second on the discharge (pressure) side of pool plumbing systems. The chart below shows you that how much water can flow through a particular sized pipe at a given velocity.

Pipe Size 5fps 6fps 7fps8fps9fps10fps
1" 13 gpm 16 gpm 18 gpm 21 gpm 23 gpm 26 gpm
1.5" 31 gpm 37 gpm 43 gpm 50 gpm 56 gpm 62 gpm
2" 52 gpm 63 gpm 72 gpm 82 gpm 92 gpm 102 gpm
2.5" 73 gpm 88 gpm 102 gpm 117 gpm 131 gpm 146 gpm
3" 113 gpm 136 gpm 159 gpm 181 gpm 203 gpm 227 gpm
4" 196 gpm 234 gpm 274 gpm 313 gpm 353 gpm 392 gpm

What's so important to take away from these numbers is that no matter what someone may tell you there is only so much water you can safely move through a plumbing system and that contrary to popular belief bigger is not better when it comes to choosing a pump. Many times it is larger plumbing that would solve the issues blamed on the pump. Too much water velocity leads to premature wear on piping, pumps, heaters, filters, and other components due to excessive pressure created in the system.