Jay, It is really not a "theory" at this point. I have found this problem at so many locations and resolved the issue that I am absolutely convinced the large trapped air pockets are causing the false alarms.
I have placed my digital LPT Data Logger on the downstream side of wet systems and recorded the system pressure on 30 second intervals for 7 day periods. The graph shows the gradual pressure increases/decreases caused by temperature changes and the exact time of the false fire alarms are always indicated by a distinct pressure increase which lasts for more than 60 seconds. This happens when the water supply increases at the same time as a cold front (or significant drop in temperature). Public water supply systems typically fill gravity tanks at night and temperature changes usually drop at night during Spring and Fall (this is typically the time of year these false alarms are most common). I use the weather channel to determine the greatest temperature drop on the night when the false fire alarm occurred. After I bleed as much air from the system as possible, the LPT Data Logger verifies that the pressure fluctuations are much less severe and the false fire alarms are a thing of the past. I have one customer where this problem occurred when there was a temperature drop and the jockey pump filled the system EVEN WITH THE DELAY ON THE FLOW SWITCH SET AT 76 SECONDS! After we bled the air from the system, the problem was resolved. LPT Data Logger was also used on this system. Yes that is correct same problem even with a fire pump......the jockey pump at this facility typically requires 20-25 seconds to start/stop, but when the underground main pressure is just right and the air pocket/temperature issue combines.......we had false fire alarms. I checked the electronic water flow switch 7-8 times and the delay was always between 70-80 seconds! In summary, air will expand and contract with temperature changes while water will not. All system have some air, but systems with a significant percentage/volume of air will allow water to flow into the system to equalize the system pressure when the pressure downstream of the alarm check valve drops below the upstream pressure. When the time required to replenish the system exceeds the flow switch delay.....the fire alarm will activate. It is even more common for systems which have pressure switches on the retard chambers. The flow switch cycling issue is also a huge problem in some instances! Refer to my previous post regarding the typical test method used by alarm technicians. I sincerely hope this helps. I imagine some of the people on this forum think I am a freak'n nut. I'm really not crazy! I will admit that I seem a little obsessed with this issue, but I am getting tired of finding the problem and none of my buddies in the Fire Sprinkler Industry want to admit this is an issue. It has become a bit of a pet-peeve of mine I suppose. Take care, Rodney K. Hamm, P.E. President/Owner Falcon Fire Protection Office (478) 953-1677 Cell (478) 396-6988 -----Original Message----- Date: Mon, 2 Mar 2009 17:07:39 -0800 (PST) From: Jay Jay Blocker <[email protected]> Subject: Re: statistics To: [email protected] Message-ID: <[email protected]> Content-Type: text/plain; charset=iso-8859-1 Rodney could you please elaborate on your theory of the air pocket tripping the flow switch. Several of us in my office are baffled. Jay _______________________________________________ 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)
