Chris (& everyone else on the forum),
I challenge you to try my suggested experiment! Even if you do not want to try it..try it with a preconceived notion that I am completely wrong. The results will be so obvious you will see my point. The plastic film on top allows you to see the dramatic difference in pressure increase (100% water vs. 50% air). My experiment is actually a closed system. I will agree that the volume is allowed to increase, but the only force which allows the plastic film to balloon is due to the increased pressure in the closed container. If the same percentage of water/air was in a sprinkler pipe, the increased pressure caused by the temperature increase would cause the system pressure to increase dramatically due to the fact that there is no change in volume (until a leak or system rupture occurs). Of course, the best test environment would be to use a sprinkler system in an oven with a calibrated pressure gauge, but most of our forum readers would never take this much time and effort. The experiment I suggested is VERY convincing if you are willing to spend 5 minutes of your time to try. By the way, I have conducted this experiment in the real world with steel pipe and significant temperature changes. I live in the great state of Georgia and I have personally witnessed the pressure increase dramatically with the control valve on the system completely closed (i.e. no possible way any water entered the system!). I have also confirmed the system pressure decrease as the temperature decreases in the same situation with no evidence of any water discharging from the system. I will go to the grave knowing I am completely correct regarding this matter (and I am really an open minded person; I am not pig headed and/or unwilling to consider a different point of view). I actually make a concerted effort to learn from other people's experiences and try to keep an open mind whenever possible. I am truly almost to the point of giving up regarding this subject. I really do have a lot of other responsibilities, but for some unknown reason, I feel compelled to continue responding to the various posts. I think I might just need some professional help! Take care & let us all know how the experiment goes, Rodney K. Hamm, P.E. President/Owner Falcon Fire Protection Office (478) 953-1677 Cell (478) 396-6988 Date: Wed, 11 Mar 2009 10:22:41 -0500 From: "Chris Cahill" <[email protected]> Subject: RE: Test/Drain at the Riser To: <[email protected]> Message-ID: <f38fd1b2a20f4909ab84c40766f01...@chris2005> Content-Type: text/plain; charset="us-ascii" With out resorting to the "think" dig I appreciate the conversation and I think most member do as well. Compressibility and expansion due to temperature are two entirely different phenomena. Compressibility I would describe the volume change as a result of pushing on something. Expansion and contraction is the rate of the molecules trying to get away from each other? Yes each play on each other in a closed system with the generic PV=T formula. Yes that's the IDEAL gas law and we are far from ideal here. And the rates of compressibility and expansion are not the same for the agents here or even related within each agent. I don't know what to say about your experiment other than it's not relevant to the issue. With plastic on top you basically have an open system that is to say the volume of the container can change. In a steel piping system the volume of the container can not change. Or at least to say it changes very small relative to the size of the system. Do your same experiment with capped steel pipe and see the results through a pressure gauge. You might need the oven or a pot of hot water. The misses at home or the boss at work might get upset if you put steel in the microwave. The other problem I see with your experiment is the scale. The changes in the water volume may be imperceptible to the naked eye. Obviously there is either some disagreement here or at least a communication issue. This is good because it will make both of us sharper. Chris Cahill, P.E. Fire Protection Engineer Sentry Fire Protection, Inc. 763-658-4483 763-658-4921 fax Email: [email protected] Mail: P.O. Box 69 Waverly, MN 55390 Location: 4439 Hwy 12 SW Waverly, MN 55390 -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Rodney Hamm Sent: Tuesday, March 10, 2009 8:27 PM To: [email protected] Subject: Re: Test/Drain at the Riser I am sorry to be so blunt, but you need to think a little about what you have stated. Air is compressible and water is not compressible. Temperature increases or decreases do not affect the pressure of a section of pipe filled with 100% water until the water begins to boil. Temperature increases will cause the pressure to increase if the same section of pipe is filled with air. Temperature decreases will cause the pressure to decrease if the same section of pipe is filled with air. If you do not believe me, try a quick little experiment. Take a completely 100% full glass of cold water (plastic would be best) pull some saran wrap over the top very tight and add a rubber band really tight to make sure no air leaks out. Make sure there are no air bubbles on top. Put the full glass of water in the microwave on HIGH for 2 minutes. No pressure builds up inside the glass because water is not compressible and does not expand. Pressure will eventually build if you let the water start to boil. THEN do the same exact thing with a glass half full of cold water. Using saran wrap and a tight rubber band, you will see the pressure increases dramatically and eventually will burst the saran wrap after the balloon effect! If you have significant trapped air pockets in a sprinkler system, the ONLY time you do not need a PRV is if you are absolutely certain the sprinkler piping does not experience significant temperature changes. High temps to low temps will cause the pressure to decrease and can potentially allow water to enter the system (i.e. false fire alarms) and low temps to high temps will cause the pressure to increase and can potentially cause damage to the sprinkler system piping (i.e. leaks, ruptures, deformation of sprinkler plugs, etc.). You stated the following: "With a static system increasing in temperature the air compresses and stabilizes the pressures." Actually, in this instance increasing the temperature the air does not compress it actually expands and instead of stabilizing the static pressure it drastically increases the static pressure. Rodney K. Hamm, P.E. President/Owner Falcon Fire Protection Office (478) 953-1677 Cell (478) 396-6988 _______________________________________________ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field)
