How to Best Regulate Pressure on Combo Riser?

6/12/2023

I'd appreciate some advice.

What's the best way to regulate pressures on a combined sprinkler (OH2) and Class 3 standpipe system?

Obviously the pressures required vary between sprinklers, 2-1/2" standpipe outlets and 1-1/2" hose rack connections.

Pressure regulating valves are expensive to put in on all connections, but I was thinking about using pressure regulating valves for the 2-1/2" standpipe outlets.

I think it's great that we can all share our combined experience on this great website - thanks in advance!

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7 Comments

Alex

6/12/2023 06:40:57 am

First, I would verify which system has the higher pressure demand. Then, I would provide PRVs on the respective system.

For your example, assuming the sprinkler system has the greater demand, provide pressure regulating valves for the 2-1/2" standpipe outlets. When doing so, ensure your drain riser is sized large enough for testing.

Pete H

6/12/2023 06:50:35 am

Pressure regulating valves anywhere your system is going to exceed 175 psi (and therefore exceed the listed pressure of many sprinkler fittings).

If you're only concerned about overtaking 175 psi when the fire department is flowing into the standpipe, then I'd advise pressure restricting devices over pressure reducing valves.

From my poor understanding, basically pressure restricting devices modify residual (flowing) pressure and pressure reducing valves modify both residual and static pressure.

6/12/2023 08:29:44 am

-When standpipe pressures (city water, building fire pump, etc.) are over 100 psi and under 175 psi, standard 2.5" hose valve, pressure restricting (valve reduced under flow conditions only) type 1.5" hose valve. 2" test riser with test ports for 1.5" valve.

-When over 175 psi, pressure reducing (valves reduced under flow and static conditions) on sprinkler (depending on components used of course, some are rated for higher pressures), and both the 1.5" and 2.5" standpipe valves with drain riser upsized as per NFPA 14 for 2.5" pressure regulating devices to 3" with test outlets.

-Or run separate risers with the pressures reduced at the base of riser to 175 psi with a larger pressure reducing valves for the low and high zones. (Remember standpipe systems need a Dual Pressure-Regulating Device Arrangement per NFPA 14. See Typical Multizone System layout in NFPA 14 too.)

-I would not include for these on an automatic system that is less than 100 psi from the city and/or fire pump since the fire department connection pressure is not part of the System Working Pressure as per NFPA 13. Of course an AHJ can tend to have a different opinion from time to time I am sure.

Casey Milhorn

6/12/2023 08:56:54 am

Without more detail, your answer will vary. Also, there are several approaches to pressure control that all could work and could meet code, some might just be more economical and/or practical than others. Mostly the solution is going to be based on the height of the building and local/state AHJ requirements. Remember that it's the firefighters that will be going in and using these hose valves when it hits the fan, with their lives in danger. I fight very hard to give them what they want, and I put their opinion above everyone else's.

You need to check EVERY fitting, device, sprinkler, etc. that will be experiencing over 175 psi and confirm to what pressure they are listed to. Remember that some have varying pressure limits by listing agency. FM vs UL may differ.

But to reiterate, the question is a little vague and would need more details to be able to provide a plan for pressure control for this project. This can be a very complicated topic and I would make sure to get someone on board that has experience in this area.

Glenn Berger

6/12/2023 09:05:57 am

Please indicate the supply side maximum pressure that you want to regulate. Initially my concern would be for the 1-1/2 inch hose having excessive pressures for "untrained" people.

Dan Wilder

6/12/2023 09:07:34 am

Sprinkler and standard 2½" hose valves in a Class I or III system have a min 100PSI (HV only) & max 175 PSI (both). The 1½" hose valves/stations have a min 65 PSI and max 100 PSI.

Not sure what your heights or pressures are but typically the 1½" hose valves require the greatest attention, then the 2½" hose valves. You can combine the 2½" hose valve & the sprinkler system downstream of the same PRV to help save on those costs (if any) but the 1½" outlets are going to require the PRV's and associated drains.

The sprinkler calculation vs the 250 GPM hose requirement will dictate the type PRV needed (they have a maximum GPM before you'll have to change to a different type of valve) but using QR reductions for the OH can help.

Ray Hardy link

6/13/2023 04:28:14 am

Thanks to all for these really useful comments. I will be allowing a 4" combined galv drain line. I was hoping that the fire truck pump wouldn't go over 150psi, but I guess it could? As Casey says, we need to make sure that the fire department get what they want and we will be in consultation with them shortly. We have asked for a dispensation to go from a class 3 to a class 1 standpipe system, because I too am worried about untrained personnel using fire hoses - the FD will advise on that I'm hoping. A pressure mapping excercise is a great idea and I'm certainly taking that on board. Thanks again!

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How to Best Regulate Pressure on Combo Riser?

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