I find it VERY interesting that you find it VERY interesting there has been
no findings. Hint of insecurity in your position?
Why would anyone try your experiment when it is irrelevant to the constant
volume container of a sprinkler system?
No one "believes water compression" is responsible for anything. It's
thermal expansion without compressible air.
"Or could it possibly be that water and air act differently to temperature
changes in Georgia than any other place in the world?" I guess that's as
valid a theory as trapped air causes excess pressure. I have only driven
through the great state of Georgia once so I'll defer to your expertise on
matters in Georgia.
You have made an extraordinary claim thus it is incumbent upon you to
provide extraordinary evidence. Your claims go against the text book
('02-7.1.2.2, A.7.5.3.2 and the handbook) and the vast field experience of
this forum. There's even the fancy math thingies with letters, subscripts
AND symbols which us PE's like.
I have the upmost confidence in my position so I'm not in any big hurry to
propose and try a valid model experiment of the situation. If I had doubts
it would be a higher priority. Given a choice I'll spend my time with
friends and family. When those priorities allow (and I have my Guitar Hero
fix for the day) you'll get feedback.
And as far as your trees and grids. Sure sounds like what 7.1.2 describes.
Imagine that the trees are OK and the grid is not and that's what the text
book covers. Coincidence I'm sure. Granted I concede once text books had
the center of the universe as Earth and the Earth was flat. I'd like to
think we've come a long way and today's text couldn't be that wrong. But hey
those that wrote those old texts probably thought the same thing, they
couldn't be that wrong. Good news if you are right we'll probably name the
principal after you. Bernoulli, Pascal, Hazen-Williams, Hamm!
If you believed your theory why are you recommending the PRV? Shouldn't
removing the air only be what you would advocate? If the PRV wasn't
required when installed then it was and still is code compliant. Why would
you need both seemingly counter solutions?
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 Rodney Hamm
Sent: Wednesday, March 18, 2009 8:23 PM
To: [email protected]
Subject: Excessive system pressure
I find it VERY interesting that it has been over a week since I
suggested/challenged the forum participants to a simple experiment and there
has been exactly ZERO responses to report any conclusions/findings.
I am wondering if anyone actually tried the experiment referenced
below....if so, I wonder why has there been no response through the forum?
Could it be that some have spent the 4-5 minutes and have decided against
posting a response because the experiment does not support their theory?
Could it possibly be that the various forum participants who believe water
compression is the root cause of high system pressures are to "old school"
and "close minded" (to use a phrase that was used to describe me..heh heh
heh..really funny if you knew me at all) to consider a simple experiment
that might in any way challenge their way of thinking? Or could it possibly
be that water and air act differently to temperature changes in Georgia than
any other place in the world?
I am having a little too much fun with this email.
On a more serious note, I was at another plant yesterday which has the same
exact problem. This is really why I am writing this email. Warehouse with 1
gridded system and 7 tree fed systems. The problem only exists for the
gridded system; the remaining 7 systems had nominal pressure differences
(0-10 psi difference) between the top & bottom gauges. On the gridded
system, the public pressure upstream of the alarm check valve was fairly
steady all afternoon at ~60 psi. At 1:50 PM, the system pressure downstream
of the alarm check valve was 190 psi. I described the problem to the plant
engineer and he wanted me to explain the problem to the plant manager. The
three of us returned to the riser at 2:10 PM and the system pressure
downstream of the alarm check valve was already up to 205 psi. We have not
even entered our really hot days of summer yet! Riser nipples on the near
main and the far main and the ITC for the system was attached to the bottom
of the far main (in other words, the auxiliary or low point drain was
converted into an ITC by installing the base of a sprinkler head at the end
of the pipe and then someone placed an ITC sign on the valve). This system
was installed prior to the NFPA requirement of a 175 psi PRV for all gridded
systems. I have recommended the provision of a 175 psi PRV, installing air
bleed off valves and removing a significant amount of the trapped air from
the system. The ITC piping "SHOULD" be arranged to flow water through the
highest point of the system whenever possible, but some people just don't
give a damn!
Rodney K. Hamm, P.E.
President/Owner
Falcon Fire Protection
Office (478) 953-1677
Cell (478) 396-6988
Date: Wed, 11 Mar 2009 15:47:19 -0400
From: "Rodney Hamm" <[email protected]>
Subject: RE: Test/Drain at the Riser
To: <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="us-ascii"
I challenge you to try my suggested experiment! Even if you do not want to
try it..try it with a preconceived notion that I am completely wrong.
Take a completely 100% full glass of cold water (plastic would be best) pull
some saran wrap over the top very tight and add a rubber band really tight
to make sure no air leaks out. Make sure there are no air bubbles on top.
Put the full glass of water in the microwave on HIGH for 2 minutes. No
pressure builds up inside the glass because water is not compressible and
does not expand. Pressure will eventually build if you let the water start
to boil. THEN do the same exact thing with a glass half full of cold water.
Using saran wrap and a tight rubber band, you will see the pressure
increases dramatically and eventually will burst the saran wrap after the
balloon effect!
The results will be so obvious you will see my point. The plastic film on
top allows you to see the dramatic difference in pressure increase (100%
water vs. 50% air). My experiment is actually a closed system. I will agree
that the volume is allowed to increase, but the only force which allows the
plastic film to balloon is due to the increased pressure in the closed
container. If the same percentage of water/air was in a sprinkler pipe, the
increased pressure caused by the temperature increase would cause the system
pressure to increase dramatically due to the fact that there is no change in
volume (until a leak or system rupture occurs). Of course, the best test
environment would be to use a sprinkler system in an oven with a calibrated
pressure gauge, but most of our forum readers would never take this much
time and effort. The experiment I suggested is VERY convincing if you are
willing to spend 5 minutes of your time to try.
Air is compressible and water is not compressible. Temperature increases or
decreases do not affect the pressure of a section of pipe filled with 100%
water until the water begins to boil. Temperature increases will cause the
pressure to increase if the same section of pipe is filled with air or has a
significant percentage of air along with some water. Temperature decreases
will cause the pressure to decrease if the same section of pipe is filled
with air or has a significant percentage of air along with some water.
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