Todd,
That was what I was talking about in my last post. You cannot
subdivide the dry piper with check valves. One reason I can think of
is because when new and they work you have one water delivery time but
as they age and leak each subdivision that does so adds time to
decompression and so to water delivery also. I've seen this problem
and so from this standpoint this recent (maybe 99) in 13 makes sense.
The other problem I can imagine is the clapper on a swing check
"glueing" itself shut due to disuse.On the one's I'm familiar with
that was never a problem.
Back to subdivision. 13 does not (and I admit I'm stretching this and
remember that I don't like the idea but I'm not the owner, designer,
layout tech or the AHJ and am merely arguing code/standard points)
prohibit check valves in dry systems. It specifically prohibits using
them for subdivision. Again, if water delivery time was what prompted
the prohibition, then testing the system with the check valves removed
and replaced by spools effectively addresses the prohibition since the
now missing clappers are not there to hold air back and so you are
getting a realistic picture of the entire system rather than just the
riser and one floor.
Would IU recommend such a scheme. Never, but not because the schema
itself is without logical merit but rather because of the ridiculous
costs and the tendency to "cheat" associated with IT&M.
Part of the argument here revolves around committee intent. Why is
this rule there in the first place (like the 52K square footage
limitation)? Is it there because it's always been there and we don't
remember why (Like 52K)? Is it there because a problem was discovered
and this is a fix (maybe like this prohibition against subdivision by
check valve in dry pipes)? Is it there because some vendor has come
out with a new product that meets a need and rules for its use are
needed (the section for ESFR)? Or is it there because someone can just
make money? We can't know unless we religiously follow the RFPs/RFCs
and the voting and have photographic memories or wish to spend hours
upon hours searching old stuff that's not catalogued or indexed.
Perhaps with the state of electronic filing NFPA can make access to
the thousands of hours of committee stuff easily accessible. I don't
think the intent is to make these deliberations opaque in any way but
they are, at this time, translucent at best.
We have Joe Hankins that can shed light on some of FM reasons and
conclusions. Steve addresses 14 intent regularly. Bamford, Dead Bob,
Roland (my neighbor that I never see) and others chime in when they
know how a committee came to a decision but these guy's memory hardly
make an archive.
Ron Greenman
...at home
On Apr 10, 2008, at 4:08 AM, Todd Williams - FPDC wrote:
Ron,
NFPA 13 (2002) sect. 7.2.3.4 states "Check valves shall not be used
to subdivide the dry pipe system." To me, that says that check
valves cannot be used for any purpose on a dry system since they
will, by their nature, subdivide a system. Since a check valve is
now required on floor controls, you can probably not install a
"floor control" on a dry system. You could install an isolation
valve on each floor and that is about it. (note to thread readers: I
did not look up the specific wording of the 13 section until I
prepared this post)
Todd
Todd, although you can't use check valves to segregate sections of
the
system you have to have the check valves. Two separate requirements.
One has to do with isolating the floor for service. The other has to
do with water delivery time.
Todd G. Williams, PE
Fire Protection Design/Consulting
Stonington, Connecticut
www.fpdc.com
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