I FULLY INTEND THAT THIS WILL BE MY LAST POST REGARDING THIS SUBJECT. I promise to make a concerted effort to make this statement true. I would also like to state that you should probably read this entire post if you have not completely tuned out regarding this subject!
I obtained my Bachelors Degree in Mechanical Engineering and I am also a FPE; I am fully aware and I understand thermal expansion. A few forum participants posted data regarding water, but refrained from including any thermal expansion data for air. My point is that thermal expansion effects both water and air. The following two paragraphs were copied from the internet: Charles's law states that when pressure is kept constant, there is a direct relationship between volume and temperature. As a gas heats up, its volume increases, and when it cools down, its volume reduces accordingly. Thus, if an air mattress is filled in an air-conditioned room, and the mattress is then taken to the beach on a hot day, the air inside will expand. Depending on how much its volume increases, the expansion of the hot air could cause the mattress to "pop." That is to say, he discovered that if a container of air were to be sealed at 0*C, at ordinary atmospheric pressure of 15 pounds per square inch, and then heated to 100*C but kept at the same volume, the air would now exert a pressure of about 20 pounds per square inch on the sides of the container. (Of course, strictly speaking, the container will also have increased in size, that would lower the effectbut its a tiny correction, about ½% for copper, even less for steel and glass.) Remarkably, if the air were initially at a pressure of thirty pounds per square inch at 0*C, on heating to 100*C the pressure would go to about 40 pounds per square inchso the percentage increase in pressure was the same for any initial pressure: on heating through 100*C, the pressure would always increase by about 33%. Water on the other hand: On heating from 0*C through 30*C, the pressure will stay essentially constant, while heating from 30*C through 100*C, the pressure will increase by about 4%. Check out the thermal expansion properties of air and water if you think I am wrong. Web site: http://www.engineeringtoolbox.com/water-thermal-properties-d_162.html In summary, I guess I am simply trying to state that trapped air pockets will create a more significant pressure increase or decrease in a closed sprinkler system than water when the temperature changes. I will absolutely admit that I cannot explain mathematically why we see such drastic pressure increases in the numerous wet sprinkler systems where we have identified and resolved these issues (based strictly on Charless Law, the pressure increases should not be so extreme), but I can state that the excessive pressure problem is completely resolved after we bleed off a significant amount of the trapped air pockets. This is not a theory, this is absolute real world action with undeniable results. Some systems relieve air for 20-40 minutes through multiple sprinkler heads (loosened enough to hear and feel the air escape from the system at the various high points). After we remove a significant amount of the trapped air, the problem is resolved. And to address the obvious question, the problem is resolved even without a 175 psi PRV (we do not always provide the 175 psi PRV, but we typically recommend them for gridded systems; some clients agree to provide them, but some decide against paying for the 175 psi PRV). I will officially let it go. I have planted a few seeds through this forum and hopefully caused a few people to think about the subject to some degree. I sincerely hope that I have not caused any animosity or hurt feelings if so, PLEASE know that I had no intentions of making anyone feel bad in any way, shape or form. I also feel compelled to state that I am really not trying to win an argument ..arguing or an obsession of being right is usually a fruitless and ultimately negative exercise. That being said, I imagine that I am now officially branded as argumentative and/or obsessive. I hope this is not the case, but I am a Big Boy and I can deal with it I guess! Over time, I sincerely hope everyone on this forum will realize that my overall intentions are to have a positive impact, learn from the forum participants experiences and share a few of my personal experiences along the way! Take care, Rodney K. Hamm, P.E. President/Owner Falcon Fire Protection Office (478) 953-1677 Cell (478) 396-6988 Date: Thu, 19 Mar 2009 09:26:38 -0500 From: "Chris Cahill" <chr...@sentryfiremn.com> Subject: RE: Excessive system pressure To: <sprinklerforum@firesprinkler.org> Message-ID: <4ea8e8951e2342039812650e425c4...@chris2005> Content-Type: text/plain; charset="us-ascii" I find it VERY interesting that you find it VERY interesting there has been no findings. Hint of insecurity in your position? Why would anyone try your experiment when it is irrelevant to the constant volume container of a sprinkler system? No one "believes water compression" is responsible for anything. It's thermal expansion without compressible air. "Or could it possibly be that water and air act differently to temperature changes in Georgia than any other place in the world?" I guess that's as valid a theory as trapped air causes excess pressure. I have only driven through the great state of Georgia once so I'll defer to your expertise on matters in Georgia. You have made an extraordinary claim thus it is incumbent upon you to provide extraordinary evidence. Your claims go against the text book ('02-7.1.2.2, A.7.5.3.2 and the handbook) and the vast field experience of this forum. There's even the fancy math thingies with letters, subscripts AND symbols which us PE's like. I have the upmost confidence in my position so I'm not in any big hurry to propose and try a valid model experiment of the situation. If I had doubts it would be a higher priority. Given a choice I'll spend my time with friends and family. When those priorities allow (and I have my Guitar Hero fix for the day) you'll get feedback. And as far as your trees and grids. Sure sounds like what 7.1.2 describes. Imagine that the trees are OK and the grid is not and that's what the text book covers. Coincidence I'm sure. Granted I concede once text books had the center of the universe as Earth and the Earth was flat. I'd like to think we've come a long way and today's text couldn't be that wrong. But hey those that wrote those old texts probably thought the same thing, they couldn't be that wrong. Good news if you are right we'll probably name the principal after you. Bernoulli, Pascal, Hazen-Williams, Hamm! If you believed your theory why are you recommending the PRV? Shouldn't removing the air only be what you would advocate? If the PRV wasn't required when installed then it was and still is code compliant. Why would you need both seemingly counter solutions? Chris Cahill, P.E. Fire Protection Engineer Sentry Fire Protection, Inc. _______________________________________________ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: techsupp...@firesprinkler.org To Unsubscribe, send an email to:sprinklerforum-requ...@firesprinkler.org (Put the word unsubscribe in the subject field)
