WorldWide Drilling Resource

61 WorldWide Drilling Resource ® NOVEMBER 2014 Terms Part 11 by Bill Corey Pentair Water Training Institute So last month we talked about Bernoulli’s Law, which has a big affect on pipe sizing. We used Bernoulli’s Law to show how friction loss happens in a system. The faster the water moves, the more loss will occur in the system and the more it will cost the end user of the system. For their sake, we recommend you keep the losses to a minimum. But Bernoulli was looking at overall losses. There are two formulas for calculat- ing friction loss in a piping system - the Darcy-Weisbach tables and the Hazen- Williams tables. There are differences, so let’s take a look at both. The Darcy-Weisbach formula looks like this: H = (F) x (L ÷ D) x (V ÷ 2G) DON’T PANIC, I’m only showing you the formula, you really don’t need to remember it. Let’s explain what is all means: H is total head loss F is friction factor related to the roughness inside the pipe L is length of the pipe D is diameter of the pipe V is average liquid velocity in the pipe 2G i s 2 t imes t he Un i ve r sa l Gravitation Constant (G=32.2 feet per second) Notice that H is total head loss, so we are talking about one long piece of pipe. They assigned a friction factor and, like Bernoulli, they used the velocity head, length, and diameter of the pipe. Hazen-Williams uses a similar for- mula, but note they are saying every 100 feet of pipe has the same friction loss. So why not take the total length of pipe and divide it by 100 to see how many 100-foot lengths of pipe you have, then multiply it by a friction factor for the type of pipe? Their formula looks like this: H ÷ 100 feet = 0.2083 x (100 ÷ C) 1.85 x (Q 1.85 ÷ D 4.865 ) You can see they did add one more factor, which was age. As pipe gets older, we know the inside diameter will reduce in size because of a buildup of scale, rust, or minerals. Of course, all of this is in a chart form - and easy to read at that. Here is part of a chart: Next month, we’ll talk about what to do with fittings. Bill Bill Corey may be contacted via e-mail at michele@wwdr-usa.com