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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