pressure reducing valve

[kolby15]

I am looking at a 6 story apt bldg that will need a fire pump to get the 100 psi residual @ top of standpipe. My customer has suggested using a 6" pressure reducing valve in the basement on the 6" main supply to the standpipes vs installing individual pressure reducing valves on each floor.

I cannot find anything that says I cannot do this, the calcs work out to allow this to happen. Are there any codes I am missing that say this cannot be done? I am looking at the 6" Tyco PRV-1.

Thanks

 

[bmlxd40]

I have seen a lot of debate on this subject. NFPA 20, 2013 edition 4.7.7.2 says pressure relief valves and pressure regulating devices in the pump installation should not be used, but then the annex for the same passage says that it is acceptable to use a PRV down stream of the discharge isolation valve.



Is it possible to size your pump to churn at 175 or less and still give you the 100 psi at the hose valve outlet?

 

[SprinklerDesigner2]

Does the system have a roof manifold?

In other words what is the elevation of your highest outlet, how many standpipes are there and what is your city water supply/

 

[LCREP]

I do not like a PRV on pumps BUT run into them a lot. See NFPA 14 on this topic they have entire section. At minimum I would recommend a test header after the PRV with pressure gauges before and after the PRV. Also a sign with the required GPM and psi before and after the PRV. When performing the annual fire pump flow test I can then compare what is required vs what we are getting. Also make sure all fittings before and after the PRV are rated for the expected flow. If the the required flow was 1200 GPM at say 220 psi before the valve and 200psi after the PRV, I would throttle the flow until I had 1200 GPM to see what psi I had. If the psi is below or above you can adjust the PRV up or down. Note NFPA 25 requires annual flow test of the PRV.
13.5.4.3* A full flow test shall be conducted on each valve annually and shall be compared to previous test results.


Sorry I do not have the section in 14, but I know it is in the standard.

 

[stookeyfpe]

Is this in the US because if it is, why can't the Fire Department just pump the standpipe? If you're outside the US, disregard.

 

[TravisMack]

There are ways around this. I am assuming that you have a large spread in your static/residual and that is why you would have a problem with churn being too high. This issue can be controlled with a variable speed pump. This essentially has a flat curve from churn to rating.

You will find NFPA 14 has an issue with this. It has to be arranged so that the failure of a single PRV does not effect more than 2 hose valves downstream of the PRV. I have seen this countered by putting two PRV's in parallel. This way, if one fails, the parallel one will function and act as required.

But, Stookey has a very valid point that should be investigated. Is this building a high-rise? Most 6 stories I see are mid-rise buildings. NFPA 14 permits manual standpipes in buildings other than a high rise. If you have 150 psi at the FDC inlet, you may have 20 psi of total friction loss in standpipe distribution piping. This will leave you with adequate pressure to get 69' in the air. If your valve is not higher than that, you may be OK with just using the FDC and manual standpipes.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

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[Rehacayli]

If this is a 6 story building, I'm guessing that the pressure on basement is below 10 bars so the pipes and the other items should hold on churn+normal times. what I've done before is put orifice plates on the outlets that reduces the pressure on the hose to 6-7 bars so i haven't used any reducing valves. Of course I've had around 100 hose connections and this had saved me a lot of money but again I did it on Azerbaijan but NFPA specialist from UK did approved that.
That might be a viable option for you maybe.