With alarm valve utilizing a pressure switch. Water that enters the alarm port when the valve opens to allow a flow the water entering the system will operate the pressure switch after the retard fills (if present). Maintenance of the drain on the retard chamber is also a contributing factor. How well the retard chamber drains and the time interval between surges or movement of the air in the system all can contribute to false alarm. A vane type waterflow switch can operate at a flow of 4 gpm according to the UL standards most operate at a higher flow but always before 10 gpm. That is really not very much water if you had a switch on the low end of the UL standard.
The most common issue with trapped air in a wet pipe system is a short ring cycle. Open a remote inspectors test valve and the air in the system is compressed and will push water down stream out of the inspectors test valve. When a backflow valve is present fresh water enters the system faster than it exits and in turn compresses the air in the system, The backflow will close when the system pressure equalizes and the compressed air will continue to force water out of the inspectors test valve. You will see a constant flow of water exiting the test valve however, no water is passing by the waterflow switch. The waterflow switch will re-set and this cycle just repeats itself. Mike Cabral ---- Jay Jay Blocker <[email protected]> wrote: > Can anyone help me understand how an air pocket would cause such concern. I > understand every other point that was made in the below message. With the > retard set at 10-25 seconds i would have to say that is one hell of an air > pocket if it trips the flow swith. I am just having trouble understanding > how an air pocket could do this. I firmly believe that we do get air pockets > in the system and they can be dealt with by air reliefe means. But if we are > talking about fighting MIC the lack of introduction of new highly oxygenated > water into the system would aid our battle. If the ITC is remote we > introduce new oxygen into the system we help MIC in it ever destructive > path. I can see both sides of the issue here and do not mean to "stir the > pot". As far as the comment of "They simple bypass the alarm or set the delays so high that flow switch cycling becomes a problem during alarm testing. " I dont have my book with me but if memory serves me correctly we have a very high amount of time in which to recieve the alarm. If you have found a situation where the alarm initiating devices have been bypassed the location of the ITC is a mood point and i would be contacting an AHJ. The location of an ITC is pointless if the alarm can never be generated. Again i am confused as to how an ir pocket would trip the flow switch so any insight into this would be helpful. Jay ________________________________ From: Rodney Hamm <[email protected]> To: [email protected] Sent: Sunday, March 1, 2009 3:38:19 PM Subject: RE: statistics If anyone has any pull or influence with the development of NFPA 13........ Please discuss the idiotic approach of installing Inspector's Test Connections at the sprinkler riser (~12 in. downstream of the flow switch). This has been considered "acceptable" by NFPA 13 since 2002 and is quickly becoming standard practice in the great state of Georgia. There are several significant reasons why this is a bad idea AND from an engineering standpoint this is a very poor design. The inevitable trapped air in the system causes or can potentially cause a number of problems: Excessive system pressure when temperatures increase, false water flow alarms due to air pocket expansion/contraction, failed water flow alarms due to cycling flow switches, increased rust on the interior surfaces of sprinkler piping, etc. >From what I have seen, most contractors or sprinkler designers who primarily install or design new systems have no idea this approach causes problems for the building owner and/or fire protection system inspectors. I can confirm these are common problems at several of the facilities I have visited over the past few years. In many instances, the only effective solution is to install a suitably located Inspector's Test Connection or bleed the air pockets using sprinklers at the highest elevations. We have installed air bleed off connections for numerous systems simply to allow trapped air to be removed from the high point. The problem is access at some facilities after the solid ceilings or other obstructions have been introduced. In my humble opinion, Inspector's Test Connections should be installed at the most remote point of each system. The connection point (prior to being piped to within 6 ft. of the floor level) should be at the highest elevation of the sprinkler system piping whenever possible. Auxiliary drains or low point drains should NOT be considered Inspector's Test Connections. I would assume it is safe to say anyone who has enough experience and personal dealings with inspections and/or problem solving (after the design phase and initial installation project has been completed) realizes that the Inspector's Test Connection serves more purposes than just testing the water flow alarms. {I have heard "the sole purpose of the ITC is to test the alarm device" so many times that I get a smile every time someone spouts it.} I simply disagree with the relatively recent change in NFPA 13 which allows this approach. I strongly believe the practice of installing the Inspector's Test Connection a few feet downstream of the water flow switch should be considered unacceptable. In many instances, the fire alarm companies and building owners have to deal with the issues caused by this poor design. They rarely if ever realize the true source or reason for the intermittent false alarms. They simple bypass the alarm or set the delays so high that flow switch cycling becomes a problem during alarm testing. We see systems with >175 psi on a regular basis caused by this problem.......some systems even peg the 300 psi gauges. On of my customers had 5 separate incidents where sprinklers developed leaks and/or popped open due to excess system pressure during Spring & early Summer of 2007. We added pressure relief valves in August of 2007 for all of their wet systems and this resolved the problem. This is a >1 million sq. ft. facility with several wet systems. False fire alarms and excess air pressure are very common problems when the ITC is not located at the most remote and/or highest elevation of the system piping. I could provide many more examples, but I think I have made my point. Black steel, moisture and trapped air allows more rust to develop on the interior surfaces of the sprinkler piping than if the majority of the sprinkler piping is full of water. Therefore, it would be safe to conclude that trapped air in the sprinkler systems will shorten the life of the sprinkler system piping. The fact that someone or some group convinced the NFPA committee to change the standard and the fact that the approach saves time and money during installation does not make it a good engineering design! There are probably a few instances where placing the ITC a few feet downstream of the flow switch should be considered acceptable due to limited or no feasible alternatives; however, these instances should be the last resort alternative rather than standard practice. Just one man's perspective!! I wonder if anyone on this forum agrees with me on this subject. Rodney K. Hamm, P.E. President/Owner Falcon Fire Protection Office (478) 953-1677 Cell (478) 396-6988 ------------------------------ Date: Sun, 1 Mar 2009 11:53:24 -0500 From: Mike Cabral <[email protected]> Subject: RE: statistics To: [email protected] Message-ID: <20090301115324.sekkv.1683217.r...@mp20> Content-Type: text/plain; charset=utf-8 A long time ago when I was a young man I did a lot of work on old systems in industrial buildings in New England. . . old textile mills mostly. I wish I had a few $ for every piece of 3/4" pipe I changed to 1" on these old pipe schedule systems. A high vent was almost always present with instructions on filling the system posted on the riser. The location of the vent or vents was stated and the order or the procedure for operating them was often posted.. Some times the instructions would advise you to open the vent while filling other times the vent was opened after the system was under pressure. If you followed the instructions you went home for the day and that was that. If you didn't you could expect a call sometime through the night because water would move as the air migrated through the system and trip the alarm. These systems were old in the late 1960's and early 1970's. . . willing to bet most of them are still in service. Venting the air keeps trapped air out of the mains and cross mains which would eliminate the air water interface which if present invites corrosion. Sometimes there is something to learn from accent history Mike Cabral ---- George Church <[email protected]> wrote: > Minimize false trips and air for MIC. > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Forest Wilson > Sent: Sunday, March 01, 2009 10:43 AM > To: [email protected] > Subject: Re: statistics > > What advantage is there to venting the air? Other than response time? > Sent from my Verizon Wireless BlackBerry > > -----Original Message----- > From: "George Church" <[email protected]> > > Date: Sun, 1 Mar 2009 10:12:12 > To: <[email protected]> > Subject: RE: statistics > > > Nothing fancy, a 1" ball valve; or an ITC-type set up if you want to get > fancy and run it out, we don't always. > > Potter has an auto air release you could also use. > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Ergo > Sent: Sunday, March 01, 2009 10:02 AM > To: [email protected] > Subject: Re: statistics > > George, > > You have a way to bleed the air off of the system at the high point? This > sounds like a good idea. Cold you explain some more on how to make this > happen? > > Thanks, > > > Ergo > > > > On Fri, Feb 27, 2009 at 8:38 AM, George Church <[email protected]> wrote: > >> Venus and Mars. I raise hypothetical questions, you hunter-gatherers > answer >> the question instead of pursuing the issue of statistics :) and how to > find >> them. Quite a change from the suggester of a group hug:) >> >> I agree on the BFP, MIC, and although we often have the ITC on a riser >> manifold, we generally have a way to bleed the air off the high point to >> avoid false signals. >> >> Good point on calculating the Expected Value, taking the frequency a step >> further and including impact. >> >> glc >> >> -----Original Message----- >> From: [email protected] >> [mailto:[email protected]] On Behalf Of Chris >> Cahill >> Sent: Friday, February 27, 2009 11:02 AM >> To: [email protected] >> Subject: RE: statistics >> >> But if you are doing a risk analysis you are forgetting the outcome side. >> For example, failure of a BFP to protect the public in theory could be >> catastrophic to many if not all on the water supply. Failure of a BFP in > a >> fire should only affect one building. On the theoretical side some may die >> from the fire and/or billions of $ lost but it ain't getting a whole city >> sick or contaminating an aquifer used by 10's of millions. So the rates >> alone are irrelevant. You need to take risk and multiply it by loss then >> you have the answer on which way to go. Don't get me wrong BFP's are a >> bunch of hooey. >> >> 1st question - about 0 for both, BFP's are a waste of money in the first >> place. >> >> 2nd - MIC is an issue we need to or will be dealing with more often. >> Remember ESF only seems at this point to be an Allied problem. I vote > treat >> the MIC. >> >> 3rd - off the end gets some/most air out reducing false alarms and >> eliminating some air/water interface rusting. MIC coatings help with the >> added oxygen in the water. I vote end. >> >> 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 George >> Church >> Sent: Friday, February 27, 2009 9:15 AM >> To: [email protected] >> Subject: statistics >> >> Just as we recently discussed that we don't know how many heads a year are >> installed, or how many have been installed in the past 100+ years, when >> discussing unexpected activations, statistics of some order of magnitude >> would be helpful in numerous other things. >> >> Which occurs more frequently, failure of a backflow to protect the public >> supply, or failure of a backflow to allow full forward flow of water to a >> sprinkler system when needed? >> >> Is the possibility of MIC greater than the likelihood of ESF from MIC >> coatings? This would aid us in deciding, on systems comprised of combo >> steel >> and CPVC, if we want to use uncoated pipe (more susceptible to MIC) or > risk >> Environmental Stress Fractures? >> >> Is it better to run the ITC off the riser and limit the new oxygen into > the >> system, or run it off the tail end and check for blockage? >> >> There are countless other items we have no data upon which to base our >> decisions. Our best guesses may be completely wrong- guess our batting >> average would be no better than 50-50, and likely the answer may be based >> on >> something more important but not considered. >> >> glc >> >> -----Original Message----- >> From: George Church [mailto:[email protected]] >> Sent: Friday, February 27, 2009 10:07 AM >> To: '[email protected]' >> Subject: RE: Fire marshall >> >> Just as a plumber would assume testing a sprinkler backflow is limited to >> the backflow portion of the test, not aware of the forward flush we're > more >> concerned about.. >> >> glc >> _______________________________________________ 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) > _______________________________________________ > 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) _______________________________________________ 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)
