No, Brad, I didn't.
What I saw was what the AHJ saw - a pump whose rated capacity was 1,275
gpm. He asked the reasonable question - what kind of pressure am I
going to have available from the municipal supply at that flow?
The calculations for P_F for the underground from the main to the pump,
and for the P_E from the main to the pump were irrelevant to his
inquiry. He wasn't suggesting Brian had done the calculations
incorrectly, or that there was somehow a greater demand from the
sprinkler system that was shown in the calculations. What he was asking
was how much pressure he'd have when the annual test at 150% was to occur.
The answer, using the formula from the marvelous book by Pat Brock
indicated that with a supply curve of 86/68/920, you could expect the
available pressure at a flow of 1,875 gpm to be around 18.8 psi.
That could also be determined by using an N1.85 log graph, but graphs
are for wimps who don't understand math.
PARSLEY CONSULTING
Ken Wagoner, SET
760.745.6181 voice
760.745.0537 fax
[email protected] <mailto:[email protected]>e-mail
www.ParsleyConsulting.com <http://www.ParsleyConsulting.com>website
On 11/18/2010 9:59 AM, Brad Casterline wrote:
Ken,
The highest flow I saw was 1560.2 from "UG" to "TEST". You saw 1875 flowing
somewhere?
***********************************
Ralphy,
From the material that Brian sent over to me, he did indeed show the
pump flowing 150% of it's rated capacity back to the municipal supply.
At that point on the supply curve the municipal supply could deliver the
flow, but it would only be at a pressure of approximately 18.8 psi
The supply curve was 86 psi static, 68 psi residual, at a flow of 920
gpm. The pump was rated at 1250 gpm at 75 psi.
And I think you're right, based on the info I read in the '10 edition of
NFPA-20, as well as the notes in NFPA-25 on annual testing, this
calculation should be done.
The FM who Brian was dealing with wasn't concerned about the sizing of
the underground, or for that matter, the demand of the fire sprinkler
system. His only concern was - apparently - what pressure is available
from the supply when the flow is pushed to 150% of the rated capacity?
Sounds to me like a legitimate question.
PARSLEY CONSULTING
Ken Wagoner, SET
760.745.6181 voice
760.745.0537 fax
[email protected]<mailto:[email protected]>e-mail
www.ParsleyConsulting.com<http://www.ParsleyConsulting.com>website
On 11/17/2010 1:12 PM, Ralphy Henderson wrote:
I've done separate calcs in the past just showing the friction losses
occurring during 150% of rated flow. Shouldn't this be done anyways to
verify that the municipal water pressure isn't getting dangerously low?
I'd just show the fire pump flowing the 150% with nothing else going on
just to verify A) The UG is sized appropriately and B) You're not sucking
the municipal water dry.
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