On Aug 7, 2007, at 9:06 AM, Ed Kramer wrote:
Roland, your post reminds me about something that's confused me for
many
versions of 14. Section 7.8.2.1 gives guidance on how to pipe
schedule a
standpipe. Simple enough: look at table 7.8.2.1. OK, then it says
". . .
to provide the required waterflow rate at the minimum residual
pressure of
100 psi at the top-most 2 1/2" hose outlet . . ." What does that
mean? Is
it a pipe schedule or is it a hydraulic calc? It can't be both,
can it?
In a sprinkler pipe schedule there is a required flow and pressure
that you have to verify at the base of the riser (accounting for
elevation to the highest sprinkler).
For a standpipe, we have the required flow and pressure at the
highest outlet but nothing about a minimum inlet flow and pressure in
order to meet it with the defined pipe sizes. For that reason, I
have always read it to mean you still have to calc it. So why do a
pipe schedule?
And another question: Table 7.8.2.1 has a heading titled "Total
Distance of
Piping from Farthest Outlet". This means the total footage of pipe
from
the underground stub-in to the physically most remote outlet, correct?
I guess literally one could say ALL pipe throughout the system but
that would require one to ignore that we are looking at a flow path
(just like the alternate 13D calc method). Having just read your
example, I see you have a different question. I have always viewed
it as going in increments, just like 13 where the initial run from
the outlet would be 4 inches up to 100 ft in your example and then 6
inch the rest of the way. Hydraulically it makes no sense to no do
the incremental approach. BAD wording combined with needing to do a
calc anyways causes me to always assign a size and leave it to the
calc to drive the final sizing and leave the schedule alone.
Roland
So as an example, if I've got 3 Class I standpipes and the total
footage of
pipe (horizontal plus vertical) from stub-in to the remote 2 1/2"
valve is
101', then the ENTIRE standpipe needs to be 6"? (flow to the most
remote
standpipe being 500 gpm, and flow in the common piping being 750
gpm and
1000 gpm).
Ed Kramer
Littleton, CO
Rich - do you really NOT require calculations on a manual even when
it is NOT a pipe schedule system?
Roland
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