WorldWide Drilling Resource

Charts by Bill Corey Pentair Water Training Institute Charts have been created so we don’t have to know all the math involved. With things like friction loss, remember, it is at the discretion of the engineer who is making the chart to decide what friction factor he will use. The higher the factor, the less friction there will be. Another chart you might use is the chart on lift and flow found in a pump company’s condensed catalog. This chart is used to help you know what perform- ance you will get from the pump you are choosing. The sample below is part of a larger chart: As you can see, this is a 10-gpm (gallons per minute) pump. I am only showing the ½-hp (horsepower) to 1-hp pumps. Notice the terms “Pumping Depth in Feet”. This is your total TDH (Total Dynamic Head) in feet as pump curves are in FoH (Feet of Head). This is a chart version of the curve. A mistake made by some of my students is they calcu- late the TDH; then when they look at the chart, say they have a pumping level of 52 feet, the pressure required is 40 psi, another 93 feet and they have a friction loss of 9 feet. This makes their TDH 154 feet. Their flow has been cal- culated at 10 gpm, so what they will do is look at this chart and say they need 154 feet, and the chart has 150 feet so it’s close enough. But then they say they need 40 psi, and when you come togeth- er at 40 psi and 150 FoH, you see the number of 2.0 gpm and all of a sudden the ½-hp pump isn’t good enough. If we follow the 150 feet on the chart down to where 40 psi equals more than 10 gpm, we are on the 1-hp pump with a flow of 11.8 gpm. The students are com- pletely confused because on the curve, they picked the ½-hp pump and now it appears they need the 1-hp. The mis- take is simple really. They added the pressure twice - once in the TDH, and again when they went to 40 psi on the chart. There is another way. If you want to use the psi on the chart, either use 0 psi at 150, or use 40 psi and remove the 93 feet from your TDH, which will leave you with only 60 FoH. Now follow 0 psi at 150 and you get 10.8 gpm; and if you follow 40 psi at 60 feet you will see the same number, 10.8 gpm. Charts can be confusing, but they don’t have to if you can put them in per- spective, know what you are looking for, and what the chart is telling you. Bill Bill Corey may be contacted via e-mail at michele@ worldwidedrillingresource.com 61 WorldWide Drilling Resource ® JANUARY 2015 " ; # 511-,(2 0) 20'5&43 %9 4+(3( ,/( $/5)$&452(23 ; 08 029'0/ # ! : : $8 $,- 3$-(3 *,6(/3,/4(2/$4,0/$- &0. "(% ,4( 777 *,6(/3,/4(2/$4,0/$- &0.