Here's another idea go do flow tests at 50 gpm increments to say 500 gpm
then jump to 100 gpm. Plot the various points and design to the graph?
This should help with your time delay portion of the question too. I guess
you should design based on 1,2, etc to the total in the remote area. Stack
of a couple dozen calcs? The problem you are running into is what we
normally do is based on simple gravity based system. We are not set up for
variable speed pumps, multiple pumps, pressure tanks, pressure restricting
or pressure reducing valves or system isolation valves that automatically
open or close based on demand and I'll throw in low tower heights in the
winter and increase system demands in the summer. But not too many
buildings burning because of this alone.
Pressure can be a bit crazy. I've had residuals higher than static before.
This was the pump used to fill the tower kicking on during flow tests. This
pump normally only ran at night and during peak demands every few summers.
With the pressure drop the system thought the tower was low, which it
wasn't. They measured tower height in the main with pressure not the tower
for pump starting and stopping.
I'm kinda thinking the Chief is right.
Chris Cahill, P.E.
Fire Protection Engineer
Sentry Fire Protection, Inc.
763-658-4483
763-658-4921 fax
Email: [EMAIL PROTECTED]
Mail: P.O. Box 69
Waverly, MN 55390
Location: 4439 Hwy 12 SW
Waverly, MN 55390
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Behalf Of Roland
Huggins
Sent: Monday, April 02, 2007 12:20 PM
To: [email protected]
Subject: Re: Flow test & fire pump
Are they considering IGNORING the pump demand portion of the initial
sprinkler calc since once the fire dept hooks up, the flow is going
to exceed 350 gpm?
Roland
On Apr 1, 2007, at 12:48 PM, Thom McMahon wrote:
> We have a municipal water system which operates at 48 psi most of
> the time, however when the flow exceeds 350 Gpm the fire pump kicks
> in and boosts the system to 145 Psi, @ 2000 gpm. Whenever a flow
> test is performed the results are always based upon the fire pump
> flow.
> As we all know most fires are contained or extinguished by one to
> three heads. Obviously this isn't enough to make the fire pump kick
> in.
> The local Fire Chief has started to question the operation of
> systems installed using the full flow of the fire pump, since even
> in flow conditions over 350 Gpm it can take as long as 2 (Two)
> minutes for the pump to kick in. The bigger concern as I see it is
> that the design for any system up to 350 Gpm should be based upon
> "NO" fire pump, with two sets of calculations one for flow up to
> 350, and another for flow over 350. This way we can be sure that
> the sprinkler heads will have the min. pressure and flow even if
> only a few go off. The other calc should be easy to prove, as over
> 350 there will be a large increase in pressure available. The
> caveat is that the higher flow calculation cannot be used to reduce
> the pipe size below those used for the lower calc. It is just a
> "Proof" calc.
>
> Does this sound like the right approach?
> No the city has no intention of changing the pump set up any time
> soon.
>
> Thom McMahon
> Firetech, Inc.
> 2560 Copper Ridge Dr
> Steamboat Springs, CO 80488-2136
> Tel: 970-879-7952
> Fax: 970-879-7926
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