I had not been following the thread because the subject title hasn't changed, but am I correct in assuming this problem does not occur with pressure switches at the top of retard chambers? James L.(Jim) Roberts, PE/SET Fluor Corporation 100 Fluor Daniel Drive - C104F Greenville, SC 29607 864.281.5149 864.281.4916(Fax)
Jay Jay Blocker <[email protected]> Sent by: [email protected] 03/03/2009 08:09 PM Please respond to sprinklerforum To [email protected] cc Subject Re: statistics Rodney i do not believe you are a nut im just not sure we are looking at the same equipment. Maybe no one else is admitting this is a problem because it may not be. I say that to say this. Lets look at basic common science here. If you have a flow switch set at 76 seconds and an air pocket tripped it that would suggest that there was enough air in one single pocket to not only move the paddle but hold it in the activated position. THis would mean the velocity of the air would have to have enough force to over power the spring and hold it for 76 seconds. None moving air could not perform this action. So if there is a pocket of air that can do this i do not believe moving the ITC would help. I would have to work with the water dept. and find a way to prevent these air pockets from entering the system. Maybe even check with businesses near bye the affected buildings and see if there domestic water has had any problems. I dont see how air pockets would discriminate between systems (honestly seems like the domestic would be more susseptible to this problem). Im not saying your wrong i am just really lost as to how this could happen. Have you tied changing out the flow switch? Jay ________________________________ From: Rodney Hamm <[email protected]> To: [email protected] Sent: Tuesday, March 3, 2009 3:26:47 PM Subject: Re: statistics 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. 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