WorldWide Drilling Resource

65 WorldWide Drilling Resource ® APRIL 2014 Terms Part 4 by Bill Corey Pentair Water Training Institute Last month, we said if you lower the pressure over water to about .4 psi, the water would boil at 70°F (21ºC). This is a true statement and I show this with the use of a vacuum pump. I ask for a volunteer to put their fin- ger in a glass of water that has been sitting on a plate connected by a tube to a vacuum pump. I ask what they feel the temperature of the water is and they say “room temperature”. This is not a guess, it is a fact - it’s been sitting there all day. I then place the glass of water back on the plate and cover it with a bell jar and turn the vacuum pump on. When the pressure in the bell jar reaches about .4 psi, the water begins to boil. I then turn the vacuum pump off and re- move the tube to allow pressure back into the bell jar. Then I take the jar off the plate, grab the glass of water, and ask the student to once again place their finger in the glass. If they believe what I said to be true, they do so, and tell the group the water is still 70°F (21ºC). If however, they don’t believe me, I must put my finger in the water first to prove it is not hot. So how does this happen in a pump? Remember the eye of the impeller is a low-pressure area. If you have ever heard of open discharging a pump, you know what you are doing is putting a valve near the discharge of the pump, then turning it on and opening the valve all the way. The water moving through the impeller is moving so fast it lowers the pressure, and the result is cavitation! The vapor bubble appears at the eye and moves to the peripheral of the im- peller where the pressure is greater; and if it is enough, the vapor bubble implodes and over time will cause damage. Bill Bill Corey may be contacted via e-mail at admin@ worldwidedrillingresource.com Here is a set of pictures showing what will happen in a pump. When watering the lawn, do it long enough for moisture to soak down to the roots where it will do the most good. A light sprinkling can evaporate quickly and tends to encourage shallow root systems. Put an empty tuna can on your lawn - when it’s full, you’ve watered about the right amount.