Yes. I believe that NFPA 291 states to get a 25% drop or the minimum
water demand required by the system. So, that flow test is not adequate
for the design that has been proposed. The city supply needs to be
tested to the demand of 2250 gpm.
It does seem very strange to have such high pressure in the pump and
churn. Additionally, putting a pump that close to demand is potential
for problems. A 1500 gpm pump gets to 2250 at 150%. If the demand is
2201 gpm, it technically meets, but is pretty tight. Most insurance
companies that I have dealt with prefer to the pump to be 90-120% of
system demand. So, they pretty much need a 2000 gpm pump for this
project in regard to that criteria. Also, going to a 2000 gpm pump
would probably knock that churn down.
Travis Mack, SET
MFP Design, LLC
2508 E Lodgepole Drive
Gilbert, AZ 85298
480-505-9271
fax: 866-430-6107
email:[email protected]
http://www.mfpdesign.com
https://www.facebook.com/pages/MFP-Design-LLC/92218417692
Send large files to us via: https://www.hightail.com/u/MFPDesign
LinkedIn: https://www.linkedin.com/in/travismack
On 4/6/2017 2:21 PM, Prahl, Craig/GVL wrote:
Can the city actually deliver your needed flow rate?Don’t let them get
by with extrapolating the flow, that line on the paper means nothing.
I got burned on a job where I was assured that they water supply was
adequate.They modeled it and assured us that there would be no
issue.When they tested, they did the basic one outlet test and
extrapolated the curve. Showed the owner and went on their way.Eight
months later when the pumps were in and everything is hooked up, there
was no way we were getting what was promised.It just wasn’t
there.Owner had to unexpectedly buy a rather large water tank.
So if you need 2200 gpm, be sure they can actually provide it.
I’m also not seeing why you need over 200 psi to make a 20 psi head work?
*Craig L. Prahl**
*Fire Protection Group Lead/SME
*CH2M*
200 Verdae Blvd.
Greenville, SC 29607
Direct - 864.920.7540
Fax - 864.920.7129
CH2MHILL Extension77540
[email protected]
*From:*Sprinklerforum
[mailto:[email protected]] *On Behalf Of
*Colin Carew (Cambridge)
*Sent:* Thursday, April 06, 2017 4:57 PM
*To:* [email protected]
*Subject:* RE: NFPA 20 4.7.7.2 [EXTERNAL]
The system demand is 2210.4 ,
*From:* Sprinklerforum
[mailto:[email protected]] *On Behalf Of
*Prahl, Craig/GVL
*Sent:* April-06-17 4:52 PM
*To:* [email protected]
<mailto:[email protected]>
*Subject:* RE: NFPA 20 4.7.7.2
You can’t use the PRV to relieve excess pressure under normal
conditions due to an over designed pump. There can be unexpected
times in a municipal supply where pressure spikes occur for various
reasons. If your pump selection puts you close to the maximum system
working pressure under normal conditions and a spike in the supply
were to occur, with no means of relief, downstream system damage could
occur.
One other concern over this selection is that it is a 1500 gpm pump
with only a 1583 gpm tested source flow rate. The pump may not be
capable of reaching the 150 % mark unless you know if the municipal
supply can actually provide more than 1583 gpm. Not knowing the
actual system demands makes it difficult to address this issue any
farther.
*Craig L. Prahl
*Fire Protection Group Lead/SME
*CH2M*
200 Verdae Blvd.
Greenville, SC 29607
Direct - 864.920.7540
Fax - 864.920.7129
CH2MHILL Extension 77540
[email protected] <mailto:[email protected]>
*From:* Sprinklerforum
[mailto:[email protected]] *On Behalf Of
*Tom Duross
*Sent:* Thursday, April 06, 2017 4:34 PM
*To:* [email protected]
<mailto:[email protected]>
*Subject:* RE: NFPA 20 4.7.7.2 [EXTERNAL]
Looks like you could be above 200 PSI churn or system pressure. The
standard (2013 referenced) does not allow you to use the relief as a
means of blowing off excess pressure above 175.
Tom
Is the 140 psi total pressure or pump rating?
The pressure relief valve comes into play if the combination of supply
pressure and pump pressure exceeds the allowable system pressure,
which for most cases is 175 psi.
So if you had fluctuating supply pressures, during a higher than
normal pressure event, the system could relieve and not damage your
downstream, 175 psi rated system.
Is this a diesel or electric?
How much pressure do you need at these heads?
*Craig L. Prahl*
Hi Forum ,
Could someone shed some light on the requirements for 4.7.7.2 . I
have a project where the quoted fire pump comes with a Pressure relief
valve and waste cone .
City pressure is 58/56/1586 , we are using a 1500gpm pump at 140 psi
to get the flow and pressure we need to supply a freezer using LP-46
heads . I find many references to the use of Pressure relief valves
being
Used but 4.7.7.2 is causing me to scratch my head .
*Colin *
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