If you put check valves on the drain lines (past the last sprinkler
but before the connection to the common) so that water can only flow
from the main to the sprinklers, then there would not be an apparent
gridding effect.
At 11:20 AM 6/28/2007, you wrote:
14.4.4.5 (2) is not referring to a ganged drain line. It is referring to a
single drain. Ganging the drains together by connecting the ends of the
branch lines is creating a grid system. Leaving this pipe out of the
calculations will not make the water flow differently. The hydraulic
calculations should provide a clear indication of the actual hydraulics in
the system. If that 1 inch pipe connecting the ends of the branch lines is
actually in the system then it should be in the calculations.
8.15.2.5.3.4 (02) is actually the most applicable section in regard to this
issue and allows 1 inch piping maximum to limit the delay of the sprinkler
discharge. Typically, for large systems, a 1 inch pipe will have little
effect. However, for small systems it could have a greater effect. The
size of the 1 inch pipe will have more of an effect if the main is 2 inches
than if it is 4 inches. The proper thing to do is to calculate the system
with the 1 inch pipe and see the effect.
Here is the applicable commentary from the handbook for this section:
Tie-in drains on multiple adjacent branch lines should be avoided if
possible, because the use of tie-in drains in effect creates a gridded
system. Gridded dry pipe systems and gridded double interlock preaction
systems are prohibited by 7.2.3.5 and 7.3.2.5. In these types of systems,
all of the air in the piping must be evacuated before a steady flow of
water is discharged from the operated sprinklers. A gridded pipe
arrangement is very likely to result in excessive time delays before
effective sprinkler discharge occurs. Tie-in drains are considered
necessary to allow rapid drainage of systems protecting cold environments.
The restriction that tie-in drains be limited to 1 in. (25.4 mm) should
help minimize any delays.
Thank You
Rahe Loftin, P.E.
Region 7 - GSA
Office - 817-978-7299
Fax - 817-978-8644
Cell - 817-371-3102
"Ed Kramer"
<[EMAIL PROTECTED]> To
Sent by: [email protected]
sprinklerforum-bo cc
[EMAIL PROTECTED]
er.org Subject
RE: Gang Drain for Attic Dry System
06/28/2007 10:01
AM
Please respond to
[EMAIL PROTECTED]
resprinkler.org
I thought I was having a senior moment, but then found it. Section
14.4.4.5 (2) (02 edition) says to NOT include tie-in drain piping in
hydraulic calcs.
Ed Kramer
Littleton, CO
>
>If it is a drain line, you would include it in the hydraulic calculations
>WHY??
>
>
>
>Jeff Hewitt, PE, SET, SFPE (Prof. Member)
>Corporate Engineer
>Bi-State Fire Protection Corporation
>636-946-0011
>636-946-5172 (FAX)
>
>This e-mail and any attachments are CONFIDENTIAL and may be protected by
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>----- Original Message -----
>From: <[EMAIL PROTECTED]>
>To: <[email protected]>
>Cc: <[email protected]>;
><[EMAIL PROTECTED]>
>Sent: Thursday, June 28, 2007 9:39 AM
>Subject: RE: Gang Drain for Attic Dry System
>
>
>> Even though the 1 inch pipe does not seem to increase the gridding
>effect,
>> it still must be provided in the hydraulic calculations where it can end
>> up
>> show some surprising effects.
>>
>> Thank You
>>
>> Rahe Loftin, P.E.
>> Region 7 - GSA
>> Office - 817-978-7299
>> Fax - 817-978-8644
>> Cell - 817-371-3102
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Todd G. Williams, PE
Fire Protection Design/Consulting
Stonington, Connecticut
860-535-2080
www.fpdc.com
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