I find it VERY interesting that it has been over a week since I suggested/challenged the forum participants to a simple experiment and there has been exactly ZERO responses to report any conclusions/findings.
I am wondering if anyone actually tried the experiment referenced below....if so, I wonder why has there been no response through the forum? Could it be that some have spent the 4-5 minutes and have decided against posting a response because the experiment does not support their theory? Could it possibly be that the various forum participants who believe water compression is the root cause of high system pressures are to "old school" and "close minded" (to use a phrase that was used to describe me..heh heh heh..really funny if you knew me at all) to consider a simple experiment that might in any way challenge their way of thinking? Or could it possibly be that water and air act differently to temperature changes in Georgia than any other place in the world? I am having a little too much fun with this email. On a more serious note, I was at another plant yesterday which has the same exact problem. This is really why I am writing this email. Warehouse with 1 gridded system and 7 tree fed systems. The problem only exists for the gridded system; the remaining 7 systems had nominal pressure differences (0-10 psi difference) between the top & bottom gauges. On the gridded system, the public pressure upstream of the alarm check valve was fairly steady all afternoon at ~60 psi. At 1:50 PM, the system pressure downstream of the alarm check valve was 190 psi. I described the problem to the plant engineer and he wanted me to explain the problem to the plant manager. The three of us returned to the riser at 2:10 PM and the system pressure downstream of the alarm check valve was already up to 205 psi. We have not even entered our really hot days of summer yet! Riser nipples on the near main and the far main and the ITC for the system was attached to the bottom of the far main (in other words, the auxiliary or low point drain was converted into an ITC by installing the base of a sprinkler head at the end of the pipe and then someone placed an ITC sign on the valve). This system was installed prior to the NFPA requirement of a 175 psi PRV for all gridded systems. I have recommended the provision of a 175 psi PRV, installing air bleed off valves and removing a significant amount of the trapped air from the system. The ITC piping "SHOULD" be arranged to flow water through the highest point of the system whenever possible, but some people just don't give a damn! Rodney K. Hamm, P.E. President/Owner Falcon Fire Protection Office (478) 953-1677 Cell (478) 396-6988 Date: Wed, 11 Mar 2009 15:47:19 -0400 From: "Rodney Hamm" <[email protected]> Subject: RE: Test/Drain at the Riser To: <[email protected]> Message-ID: <[email protected]> Content-Type: text/plain; charset="us-ascii" 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. 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! 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. 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 or has a significant percentage of air along with some water. Temperature decreases will cause the pressure to decrease if the same section of pipe is filled with air or has a significant percentage of air along with some water. _______________________________________________ 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)
