Rodney said "It is an indisputable fact that trapped air is a huge problem in gridded systems and THE reason why pressure relief valves are required on gridded systems is specifically because of the trapped air in these systems."
Sorry it's the LACK of trapped air that is the problem as it relates to pressure. I suggest you read '02-7.1.2.2 and the handbook. If you have air you don't need a pressure relief on a system. Why? It's right in the text of the standard. Air is compressible. A spring if you will. For our purposes water is not compressible. With a static system increasing in temperature the air compresses and stabilizes the pressures. That's what the pressure tank on your well is doing, that is what an expansion tank on an anti-freeze is doing. Take the air out and there is nothing to compress. Minor temperature fluctuations then radically change pressure. I can show you systems that all the air has been deliberately removed. It takes a cup of water to change the pressure a couple psi. Ever opened an inspector test valve and waited 30-60 sec for the flow switch to change position. That's the trapped air expanding. Ever opened one and the flow switch moves immediately that's no air. For this purpose ignore the delay watch the lever/paddle position. A generalization gridded systems don't have air in them is also false. It's exactly related to the location of the ITV. If the ITV is at the end of the system on a grid air might be removed while filling or testing. If the ITV is at the riser (and there is no air relief remote) there is a similar amount of air in the system as a tree. OK all things being equal a gridded system has less volume compared to a tree system because of pipe size. But the volume of the system is similar in magnitude. I'm with Mark riser ITV with air relief remote and pressure relief someplace as the best of practice for all systems but I'll add not the minimally acceptable practice. 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: Monday, March 09, 2009 5:25 PM To: [email protected] Subject: RE: Test/Drain at the Riser I am writing this response on behalf of any forum members who do not completely understand some of these issues, not as a direct response to Mark. The following two paragraphs are from NFPA 13 (2002): 8.16.4.2.1 An alarm test connection not less than 1 in. (25.4 mm) in diameter, terminating in a smooth bore corrosion-resistant orifice, giving a flow equivalent to one sprinkler of a type having the smallest orifice installed on the particular system, shall be provided to test each water flow alarm device for each system. A.8.16.4.2 This test connection should be in the upper story, and the connection preferably should be piped from the end of the most remote branch line. The discharge should be at a point where it can be readily observed. In locations where it is not practical to terminate the test connection outside the building, the test connection is permitted to terminate into a drain capable of accepting full flow under system pressure. In this event, the test connection should be made using an approved sight test connection containing a smooth bore corrosion-resistant orifice giving a flow equivalent to one sprinkler simulating the least flow from an individual sprinkler in the system. Believe me when I say there are many good reasons for the following text: "This test connection should be in the upper story, and the connection preferably should be piped from the end of the most remote branch line." The fact that so many designers/engineers/installers have decided to simply ignore this sound advice is perplexing to me. Mark wrote the following: "Placing the ITC at the end of the system will not guarantee removal of all air from the system. We specify an air bleed valve be located at the high point(s) of the system for that purpose." Nobody said anything about guarantees, I just think we should following good practices and not be so focused on convenience and/or increasing the profit associated with the job. What about systems which have sprinkler piping above fixed ceilings or suspended ceiling tiles? These systems are not very common now are they (sarcasm)? Most, or nearly all, contractors in my area do not install "air bleed off valves"; many probably never even considered the need because they are completely unaware that there is a problem. In many instances these "air bleed off valves" can be very difficult to access; why not just follow the GOOD advice outlined in NFPA 13 Section A.8.16.4.2? Do your customers, the alarm company technicians and the future sprinkler contractors (the ones who drain the system to add two heads in the new bathroom) a favor. Provide a suitable ITC and allow everyone who tests or works on the system to flow water through as much piping as possible and also through the piping located at the highest portion of the system. Mark also wrote the following: "The problems associated with air in the system are valid; that's why a means should be provided to remove the air. But excessive pressure from temperature rises is not one of those problems. In fact, it is precisely because of trapped air that most tree systems don't have excessive pressure problems. The grids tend to have these issues because air can't be as readily trapped. That's why gridded systems should have a pressure relief. Of course, if you facilitate the removal of most air from a tree system, then a pressure relief is warranted on that system as well." In a more direct response to Mark, I really do not know where to start. It is an indisputable fact that trapped air is a huge problem in gridded systems and THE reason why pressure relief valves are required on gridded systems is specifically because of the trapped air in these systems. The industry had a significant problem with leaks and accidental system activation due to air pockets and temperature changes prior to the requirement of pressure relief valves on these systems; the PRV simply prevents the system pressure from exceeding 175 psi. The systems were experiencing system pressures well above 175 psi (sometimes >300 psi) specifically due to the trapped air and temperature changes caused by weather fluctuations. In summary, the following is simply my personal opinion: The fact that NFPA 13 allows the ITC to be located at the riser does NOT mean this is a good idea or a good design. I sincerely thought I was through posting any responses regarding this subject, but I simply could not refrain in this instance. Mark, please do not hold any hard feelings towards me, I am simply trying to help the industry in general and pass on a little of my knowledge through this forum. Take care, Rodney K. Hamm, P.E. President/Owner Falcon Fire Protection Office (478) 953-1677 Cell (478) 396-6988 Behalf Of Mark Sornsin Sent: Monday, March 09, 2009 6:44 AM To: '[email protected]' Subject: RE: Test/Drain at the Riser Pardon me if this is ground that was already covered- I specify the Inspector's test Connection to be located at the sprinkler riser. This is NOT something that is new to NFPA-13 either. E.g., the 1996 edition (4-15.4.2) does not require the location to be at the riser - it doesn't specify any particular location. Commentary in the handbook that year specifically states that the purpose of the connection is to "verify the operation of the water flow alarm device(s)." The appendix dialogue recommends locating the connection at the remote location of the system - but this is by no means a requirement. Placing the ITC a the end of the system will not guarantee removal of all air from the system. We specify an air bleed valve be located at the high point(s) of the system for that purpose. I know there are automatic air releases that can be installed as well. The problems associated with air in the system are valid; that's why a means should be provided to remove the air. But excessive pressure from temperature rises is not one of those problems. In fact, it is precisely because of trapped air that that most tree systems don't have excessive pressure problems. The grids tend to have these issues because air can't be as readily trapped. That's why gridded systems should have a pressure relief. Of course, if you facilitate the removal of most air from a tree system, then a pressure relief is warranted on that system as well. Locating the ITC at the riser will help reduce the amount of new air into the system, as well as reduce the amount of freshly oxygenated water as a result of testing. This will reduce the potential for additional internal corrosion resulting from the oxygen in the system. (I seem to recall that this logic is used 'Down Under' as a means to extend the life of system piping) So, given that the purpose of the ITC on a wet system is to test the flow alarm, it makes more sense to have it at the riser where it is more convenient to facilitate the testing. Removal of air should be completed by air bleed valves or automatic air releases. Mark A. Sornsin, PE Fire Protection Engineer Ulteig Engineers, Inc. 3350 38th Avenue S. 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