Another maximum pressure limitation question

[rmarsenault]

Hi folks.
I'm new here (posting that is). I have browsed this forum several times over the last few years. You guys are knowledgeable and it is nice to see such dedicated individuals in our field.
That being said, I am an engineer in Canada and my company is involved in fire protection engineering.
On a recent project, I designed the sprinkler, standpipe and fire pump system for a new 8 story office tower.
The AHJ (for lack of understanding) wanted NFPA 14 standpipe code followed to the letter. Therefore the standpipe system was required to be automatic and hence as you know have 100 psi available the remote hose connection. To achieve this a fire pump was required.
The static pressure was 45 psi and the pump rated at 110psi @ 750 gpm had a churn (no flow) pressure of 125 psi.
I specified a flat pump curve as I knew I had to have the maximum noflow pressure below 175psi as required by both NFPA 20 and NFPA 13(we didn't want to use high pressure fittings etc.).
So my no flow pressure was 45 psi + 125 psi, = 170 psi, below 175 psi.
Just the other day at the commissioning, in presence of the owner and contractor, during the pump test it was observed that the pump no flow pressure was 133 psi. Not 125 as specified. Doing the math, the max pressure is actually 178 psi. Now the owner and the prime consultant engineers are concerned that this exceeds what is required by code.
The parties involved are looking to me for advice and are wondering if pressure regulating devices should be installed.
Anyway I am wondering if any of you have had this case before and what do you think?
Personally I have noted pumps during testing always seem to give a little more than their design specs, but in this case I made it clear to the pump manufacturer that it was critical that the pump have the flat curve due to running so close to the max pressure condition...

regards

Rick M. Arsenault P.Eng
R M Arsenault Engineering Inc.
P.E.I., Canada

http://www.rmarsenault.com

 

[TravisMack]

Your max pressure is 178. It is likely that all of your pipe and fittings are rated for the higher pressures. It is typically the sprinklers where the issue comes into play. The 3 psi equals about 7' of elevation. If you have sprinklers more than 7' above the elevation of the pump discharge, then you may be OK. If you have heads <7' above the pump discharge, then you may need high pressure sprinklers. You also may be able to get away with putting a PRV just for the lowest level of sprinklers and not have to worry about it above that level.

Good luck with the project.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[LCREP]

I am sure calibrated gauges were used on the test. AND if they were calibrated, what was the gauge error?? .5% is one expensive gauge, most are in the 1-2% range. See where I am going with this. OK if we had 190 psi I would be concerned, 178 psi, I am not.

****************************************
Fire Sprinklers Save Firefighters’ Lives Too!

 

[rmarsenault]

Hey thanks for the advice.
I went through the specs of the equipment downstream from the fire pump and determined that the fittings are rated for 750psi and the sprinklers (victaulic v2708) are rated for 250psi. As NFPA states...where portions of the system have components rated for less than 175 psi..then you need to install prv's etc. So in my case I don't need them.

Cheers

Rick M. Arsenault P.Eng
R M Arsenault Engineering Inc.
P.E.I., Canada

http://www.rmarsenault.com

 

[SprinklerDesigner2]

LCREP,

I've always been accused of being anal when it comes to using certified gauges. I have often said (and you all are tired of hearing about it) I can make a lot of mistakes and live with it but the one mistake I never want to see is when an erroneous water supply.

Do an accurate flow test and give yourself a 10 psi safety factor and you should never have a problem.

I don't eve like accepting a water supply test from a fire department because I often wonder if they know how to perform a test correctly an all to often I've seen them use gauges that were obviously cheap to begin with and never calibrated.

I get my gauges calibrated every January and this year I purchased two new ones that came to about $225 for both which included the calibration.

http://img96.imageshack.us/img96/3228/calibrated.jpg

At worst case I am off 0.30% or 0.04 psi which is pretty durn accurate.

I like Daughtridge and they get them to you within 72 hours. Best investment a sprinkler company can make.