Richard,
That is a very interesting bit of history. I believe that you helped to
open some eyes. This is one of the places that I was heading. With a 4
inch drain, this situation can get pretty out of hand. The 4 inch
interconnected drain was large in relation to the main and branch lines.
What you described was a way of getting the hydraulic calculations to work
but inhibited the time to get water to the inspectors test. This same
condition can be scaled down to a 2 inch main and 1 inch drain with 1.25
inch branch lines. Believe it or not, flowing 15 heads in a 1950 square
foot area with a 1 inch interconnected drain will gain about 4 psi than
without the drain.
Now I have to retrograde here and try to believe that the code committees
anticipated the advantage of the interconnected drain against the time to
get water to the inspector's test. In other words, you could indicate that
the interconnected drain provided just enough extra pressure to get you
into the required safety cushion but does not inhibit the time to get water
to the inspectors test. However, going along with the comments that
Chapter 14 does not require the drain to be in the calculations I have to
wonder if this is a situation where the contractor could include it because
it is not prohibited by code to just get the pressure cushion he needs.
With a large system the 1 inch drain does not affect the time the water
appears at the inspectors test and a small system inherently does not have
a problem with time to get water to the inspectors test.
So, having said all of this, I am now convinced that, for my reviews, I
will side with the folks that believe that the interconnected drain should
not be included in the hydraulic calculations.
Thank You
Rahe Loftin, P.E.
Region 7 - GSA
Office - 817-978-7299
Fax - 817-978-8644
Cell - 817-371-3102
"Richard Mote"
<[EMAIL PROTECTED] To
nkler.com> [email protected]
Sent by: cc
sprinklerforum-bo
[EMAIL PROTECTED] Subject
er.org A brief history of gang drains
06/28/2007 01:34
PM
Please respond to
[EMAIL PROTECTED]
resprinkler.org
Approximately a year after the prohibition against gridded dry systems
appeared in NFPA 13 (I think 1986 but I could be wrong). I went to work for
one of the manufacturers that is now part of TYCO. One of the first
complaints I received as the new technical service manager was; WHY WON"T
YOUR @&%$&@ VALVE TRIP IN TIME SO I GET WATER TO THE INSPECTORS TEST IN 60
SECONDS? I Then proceeded to try to get information as to the system
configuration. The answer was 6" Crossmain 2" lines and a 4" gang drain.
When I explained to him that what he was describing was a DRY GRID. Oh no
he
said dry grids were not allowed, but there was nothing in the code limiting
the size of the gang drain and/or precluding their use in the calculations.
This was the first of many similar calls I received over the next year or
two. So I sent a proposal to the NFPA 13 committee suggesting that gang
drain sizes be limited to 1", a check valve be installed at the tie in
point
to the drain line and the drain line be excluded from the calculations.
They
excepted the 1" size limit and excluding the drains from the calculations.
They rejected the check valves as being too costly and something else to go
wrong.
Richard L. Mote
Designer
Rowe Sprinkler Systems, Inc
----- Original Message -----
From: "Roland Huggins" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Thursday, June 28, 2007 1:45 PM
Subject: Re: Gang Drain for Attic Dry System
> It IS black and white. That's what I meant by the drain requirement
> trumping the grid restriction.
>
> Roland
>
> On Jun 28, 2007, at 10:33 AM, Todd Williams - work wrote:
>
>> Am I missing something here? 8.15.2.5.3.4 states: 'Tie-in drains SHALL
>> be provided for multiple adjacent trapped branch lines.....'. Shall is
>> just a grammatically correct way of saying y'gotta. If you have the
>> multiple adjacent trapped branch lines, they have to be connected with
a
>> tie-in drain. Section 14.4.4.5 says not to include them in hydraulic
>> calculations. To me, that's a pretty open and shut deal. Does it create
>> a gridded dry system, technically yes, but to me, this section says
that
>> this arrangement is allowed. Keep in mind that the cross sectional area
>> of 1" pipe is roughly 1/4 of the CSA of 2" and 1/16th of 4". That
>> creates a very different scenario than say 4" and 3" where the ratio
is
>> 9/16. It would be interesting to check trip times of a system with the
>> tie-in drains attached and one where they are plugged off.
>
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