WorldWide Drilling Resource

Dry Run by Bill Corey Pentair Water Training Institute This is not only a fault; it has a lot of meaning in the pump world. Dry run means the pump is out of water; in other words, it has lost prime. I’ve said many times in my training schools, if a pump is not primed it is a fan! All it will do is move air. This is one way to test a pump. What some don’t realize is even a submersible has to be primed. If you don’t have water in the first impeller, you don’t have prime, and the pump is called air locked. This can happen when you have a well which is plugged. Or if you have a low recovering well, the pump can pump down all the way. I was traveling with Butch, a cus- tomer in central Minnesota, and we went to his customer’s house. The complaint was a lack of pressure. When we got there, he had a like-new 220-gallon air- over-water tank with 60 psi in it. I said, “What’s wrong with 60 psi?” He said to follow him, and we went outside where he handed me a hose and turned it on. The water, of course, came spraying out, and once again I asked, “What’s wrong with this pres- sure?” He said to just wait. Sure enough, in a minute or so the flow slowed to where I could put my thumb over the hole in the hose and stop the flow of water. I set the hose down and went back to the basement and looked at the tank. The pressure in the tank was only 8 psi and I heard a glug glug , whoosh . I looked around and heard it again and saw the pressure go up 2 psi. I knew then what was happening. When Butch and the customer came in I said, “Butch listen to this.” Once again, we heard glug glug , whoosh . So I asked, “What do you make of that?” Butch said it sounded like the well was running out of water. I agreed. What happens when a submersible pump runs out of water? Air gets pulled into the pump and the check valve imme- diately closes. More air gets pulled in and what water there is in the pump is pushed out through the suction. The pump air locks or runs dry till enough water can get above the pump to com- press the air in the pump and fill up the first impeller. Once the water gets to the first impeller, it can be pulled in to open the check valve and force the water out. The glug glug was the water being pulled in. The whoosh was more air coming in causing a loss of prime again. Next month, let’s talk about how we detect this fault. Bill Bill Corey may be contacted via e-mail at admin@ worldwidedrillingresource.com 72 JUNE 2013 WorldWide Drilling Resource ®