WorldWide Drilling Resource

64 MAY 2014 WorldWide Drilling Resource ® Terms Part 5 by Bill Corey Pentair Water Training Institute Pictures are worth a thousand words. So what did you think of those pictures last month? No, they were not 100% accurate, but they definitely got the point across. Those vapor bubbles are very dangerous and will cause a lot of damage that will cost you lots of money to fix. So the best thing to do is prevent them from happening. And that’s why I’m talking about this topic! Cavitation is completely avoidable as long as you know what is causing it. Hopefully now you do. It is caused by a low-pressure area in your system. The answer should be very simple...don’t allow a low-pressure area in your sys- tem, and you avoid cavitation. So how does the low-pressure area get in your system? Well, we looked at one example last time, the open dis- charge problem. But there are other things, like an elbow right at the suction of the pump. We have always suggest- ed you allow at least six to seven pipe diameters between a fitting and the suction of the pump. There is a very good reason for this. When water is forced to change direction, it really wants to object to it. Because of the weight of the water, the momentum of the weight wants to move the water in a straight line. And don’t forget, there is also pressure push- ing the water straight. Bottom line, it doesn’t want to turn or go in a different direction. You are forcing it to, and it will react to it. Here is another picture. This time it is water going around an elbow. As you can see, the water wants to go straight, but the elbow is forcing it to turn. So a lot of the water moves to the outside edge of the pipe which decreases the area it is moving through and, accord- ing to Bernoulli, will increase the veloc- ity which leads to a decrease in pressure. If you turn the picture upside down, you will notice it is still the outside of the elbow the water wants to move through. Remember, with a higher velocity which lowers the pressure, you could see the water convert from a liquid to a vapor. If this happens in a pipe, yes it can, the vapor bubble stays near the outside edge, no matter which way the pipe is facing. This is because of the fact there is little water on the inside edge, so a higher pressure will be there push- ing the bubble to the outside until the bubble can no longer take the pressure and it implodes. Next month, we’ll see what that looks like. Bill Bill Corey may be contacted via e-mail at admin@ worldwidedrillingresource.com Flow around an elbow. Jim [Kuebelbeck]: Ever since you have been provid- ing interesting articles to WorldWidee Drilling Resource ® , I have read them with an open mind. I have admired Ronnie and her staff for the product they provide for all of us interested in the natural resources of this wonder- ful earth that we get to live on, and how to retrieve them. Ronnie is a great example to the rest of us. Your recent article in the April 2014 edition expresses a humble attitude and a reasonable hypothesis and analogy of the infiltration, conduction, storage, and discharge of ground- water... I wish you continued success. Sincerely, S. Bryce Montgomery Flow around an elbow.