High pressure in standpipe system

[skdesigner]

Being a prairie guy, I don't do a lot of sprinkler/standpipe systems in high rises. This means I don't deal with >175psi too often. Designing a system for a 36 story, two stair condo at the moment, and I am looking at very high pressures at the lower levels in order to hit 100psi @ 250gpm at the top of the most remote standpipe (while flowing a total of 750gpm).

The most obvious solution would be to separate into two vertical zones of high and low pressure using a large pressure regulating valve set to 175psi in the basement. However,

NFPA 13-2010 7.2.4(3) mandates that the failure of a pressure regulating devices cannot allow high pressure to more than two hose valves. Is there any way around this requirement short of installing 2 1/2" prvs + 3" drain riser up the tower until static falls below 175? Has anyone installed two large pressure regulating valves in series to meet this requirement?

My strategy is to feed the lower floors before the pump, and use steel pipe and 250 psi standard spray heads until pump churn + city static drops below 175 psi. I will then continue up with blaze pipe and res sprinks to the top.

Any advice from the high rise pros here is appreciated!

Thanks in advance,

Steve

 

[TravisMack]

I have seen them installed in parallel to get around this restriction. Depending on the valve chosen, you may also need a smaller one in parallel as well for the low flow condition. I have seen (2) 6" and (1) 2½" valve all installed in parallel.

I had always heard that these valves fail closed when they fail. If that is true, putting them in series would not be the best. If that is not the case, then series would be fine.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[skdesigner]

Thanks for your reply Travis. I am trying to get my head around the parallel installation. Would the valves not need to be installed in series to meet the requirement (if one fails, there is another in the line to knock down the pressure)? If the installation were parallel, there would be nothing to limit pressure downstream of the failed valve correct?

Maybe I am just not picturing it correctly in my head.

Thanks again for the help.

 

[DavidCR]

I´m not shure what is the best option for your case, but there are a lot of posts dealing with this, you could do some search on threads for example:

thread184-263835
thread184-299740

Related info...

http://www.usfa.fema.gov/downloads/pdf/publications/tr-082.pdf

http://www.cla-val.com/pdfs/B-Fire_Products_Brochure.pdf