Rather normal issues, we've had a few in these parts as well. All easily
explained.
"air cools it thins and this could create an imbalance in the pressure
differential at the valve, thus allowing the vale to trip." Well thins
isn't the right wording but yeah. Remember PV=nRT. Temperature drops
pressure drops (volume of the piping remains the same). This is what the air
compressor is for. Perhaps something in the air line or the compressor
isn't right. If the pressure drops below the trip point the valve trips. A
properly working air compressor prevents this trip.
"Another dry system froze due to water in the system". Yeah they all have
water in them. After hydrotesting the inside is wet, after full trip
testing in theory every 3 years the pipe is wet, in the summer the air
compressor adds moisture. When it cools any moisture in the air condenses
out to form water (then ice below 32). This water accumulates in low spots
like poorly sloped pipes and weld bellies or wavy pipes. This is why
sloping is so important in dry systems. I used to carry a level when I did
inspections. I was told by every fitter they never saw an inspector climb
through attics with a level. Fill the pipe diameter with water and you have
a goo chance at a break. What I also see is low point drum drips not
maintained also as a cause. A rule of thumb, if it breaks the first year
it's probably an installation error. If it breaks later it's probably
maintenance issue. Just my experience leading to my rule of thumb.
This is the time of year for this stuff. Rather normal and arguably
shouldn't be. The other peak time is after a long cold snap and it gets
above 32. One year St. Paul Fire went to 29 freeze ups in 12 hours. These
were both wet and dry systems and a variety of causes. A vast majority were
occupants doing stupid things like leaving doors open to smoke and not
fixing heaters they knew were out in entry lobbies. The day was about 38
degrees with the preceding 4 weeks below +20 and several days stretches
without getting above 0. Another year we had a lot of swings back and forth
between +40 and -0's. Had a lot of drum drip break. Some 4 times in a few
weeks. Imagine that no draining of drum drips and they break filling the
system the first time. Gets cold and the wet pipes don't fully drain. Get
back above 32 and the ice turn to water and runs to the drum drip. Goes
cold again and to our surprise (not) the drum drip freezes again.
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 Smith, Steven
D. (CSFD)
Sent: Wednesday, December 17, 2008 9:47 AM
To: [email protected]
Subject: Dry Pipe System Dilemmas
Thought I'd tap the vast knowledge of the group here.
Over the past couple days we've have numerous sprinkler breaks due to
frozen pipes. The part that perplexes me is dry pipe systems.
We have had at least a couple dry pipe system activations/breaks with no
apparent reasoning as to why or how water would be in the system.
One dry pipe activated/tripped, for no apparent reason. This charged the
system and caused the fire pump to come on. Upon investigation, no water
leaks of any sort were noted. A roving sprinkler contractor stopped in
and said that when air cools it thins and this could create an imbalance
in the pressure differential at the valve, thus allowing the vale to
trip. I suppose this could happen if the pressure differential between
the air/water was within a few psi but other than that, it doesn't make
sense to me.
Another dry system froze due to water in the system (unknown as to how
much water was left in the system) but we can't figure out how the water
was in the system. The only explanation we have at this time is water
was left in there or never properly drained.
Anyone else have any suggestions as to why dry pipe systems would
activate and/or have water present in them enough to cause breakage from
freezing?
Thanks for all insight.
Smitty
Steven Smith, CFPS | Fire Protection Engineer II
Colorado Springs Fire Department | Office of the Fire Marshal
Technical Services | 719-385-7362
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