AWWA JAW55966

When they install a branch from a water distribution main, water utility managers often debate the benefits of using a tap as opposed to shutting down the line to install a T-fitting. Part of the discussion centers around the fact that a tap, especially a size-on-size tap, will have a smaller orifice size than will a T-fitting. The concern is that this will lead to additional head loss and decreased capacity. For low-flow conditions, this loss in capacity is negligible, but during fire flows, this loss can become significant. This article reports the results of experiments that indicate the loss of carrying capacity in distribution systems is not significant as long as the orifice (tap cutout) is greater than 90% of the pipe size.