Rodney,
Nice work. One question, though. If the sprinkler system is in a
temperature controlled space, why would outside air temperature cause
pressure fluctuations? Couldn't this be caused by additional pumps
activating to fill tanks and the pressure increases are a result of
this? Bleeding the air could eliminate compression in the system,
from whatever cause, thus lowering the false alarm problem. Have you
conducted your experiment in all four seasons?
At 05:26 PM 3/3/2009, you wrote:
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
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Todd G. Williams, PE
Fire Protection Design/Consulting
Stonington, Connecticut
www.fpdc.com
860.535.2080
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