PRVs for Static or Flowing Standpipe Over 175 psi?

1/25/2023

I have a plan reviewer that is not accepting our proposed design for a manual standpipe calculation.

The calculation shows a required pressure on the fire department pumper truck to be a minimum of 217 PSI.

It has been confirmed that the pumper truck can reach and/or exceed 250 PSI.

The AHJ is requesting that we increase the standpipe from 4-inch to 6-inch, which is not alleviating the higher pressures as we are still above 175 PSI.

This would be a first for me to have to install pressure reducing hose valves on a manual wet standpipe.

My understanding per NFPA-14 (2016) 7.2.3.2 is that this is only an issue when the static pressures on the systems exceed 175 PSI (city static is 113 PSI).

So in essence, we are advising the fire department pumper truck operator to dial his pump up to 217, but this wouldn't be static, as they would be flowing out of the hose valve(s), correct?

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8 Comments

Dan Wilder

1/25/2023 07:46:57 am

This got long...sorry

TL:DR - You are correct by the section specific to static conditions. Talk to the reviewer about a middle ground but make sure you're not fighting established codes/standards.

So, NFPA 1901 Section 16.2.3 shows what the fire department apparatus are to provide when equipped with a fire pump (just for future reference) so I am assuming the pumper truck in question is rated to provide at least 1500 or 2000 GPM (no mention on if this is a 750 or 1000 GPM demand). Most AHJ's only allow 150PSI without an appeal process (in my area at least).

By the letter of NFPA, you are correct in that the section specifically references a static condition requirement for a need for a pressure reducing hose valve. Is there language in the fire code requiring a maximum PSI to be used or the ability to use the available apparatus open to interpretation?

NFPA 13e Section 6.2.3 says the standpipes "should be charged to give the desired working pressure on the standpipe being used." i.e. static pressure....but...

Section 6.2.4.2 - Pump discharge pressure in excess of 200 psi (13.8 bar) should not be used unless the standpipe system has been designed to withstand higher pressures as indicated on the sign at the fire department connection.

The assumption that there is always water flow to avoid a static condition is unlikely due to initial staging and then repositioning efforts by a responding crew(s) and no crew wants to go into a fire without a charged line ready and available not to mention the lower floors will always have higher pressures. Now, the driver engineer should be monitoring the pump to adjust for the needs of the crews on the floors but if the pump is dialed in at 217PSI at whatever flow is needed and one or more crews shuts down a nozzle, that 217 just went up.

I have had projects like this in the past where signage at the FDC and warning signage at the hose valves for higher than 175PSI working pressures allowed the design & install. I would have the conversation with the reviewer and maybe their boss and/or the Fire Marshall. Maybe a middle ground where you provide 6" (as needed) pipe to bring the required PSI down as much as possible and use standard hose valves...it beats PRV's and the associated express drains.

There is a little precedent for your situation as shown below.

https://community.nfsa.org/blogs/vincent-powers/2021/08/05/the-automatic-truth-about-manual-wet-standpipes

Anthony

1/25/2023 08:18:17 am

In defense of the AHJ and maybe common sense I think it would be obvious that the hose wouldn't be open the entire time the fire truck is providing supplemental pressure and flow to the standpipe system. There will be instance of static conditions in that system and on that fire hose. If the AHJ is the fire marshal it will their people that will have to deal with the over pressure in the system in an emergency, just as a reminder of their point of view.

Alternatively if the view is that the sprinkler system will be exposed to over pressure, the system is tested at 200 PSI (higher than the rated 175 psi operational pressure) or 50 psi over operational pressures. So test your sprinkler systems at 267 psi for 2 hours. I think that would make for a reasonable argument that the system is able to handle temporary fluctuations in pressure in testing and emergency conditions.

Casey Milhorn

1/25/2023 08:26:19 am

Dan nailed it again. I would definitely ask what their departmental procedure is when hooking up to a manual wet standpipe. That should help you find some middle ground as Dan says. I almost always plan on 6" over to the split of the two standpipes, unless I'm dealing with a 4 story hotel/motel/apartment with a small foot print. The assumption is that the engineer will deliver the amount of supply needed whether on the first floor or the top floor. I think PRVs in a manual wet standpipe system is a BAD idea. As they say, keep it simple. I've never been a fire fighter, but I would rather deal with 200 psi then have to deal with 75 psi because of a faulty or wrongly adjusted PRV in a life or death situation.

Eric R

1/25/2023 09:28:40 am

This is throwing up some pretty big red flags for me.

If the demand required is 217 you would have to assume that valves will be opened and closed without instant pressure correction at the pumper truck, and that static pressures on the system would be that or higher at-least temporarily.

"7.8.1.2.1-The pressure required at the fire department connection for manual standpipes shall not exceed the working pressure of the system components of the standpipe system or sprinkler system when the system is a combined system." Was added in the 2019 edition but should be self-evident regardless of edition adoption.

I'm with the AHJ here that the layout should be re-arranged to get the PSI down to 175.

I'd also really want to know more about this building arrangement where swapping to 6" pipe doesn't significantly drop the required pressure.

Jonathan

1/25/2023 10:15:40 am

I recommend you first reach out to and consult with the local fire department / AHJ to better understand their concerns. Start by learning about their department standpipe standard operating procedures (SOPs). It may be as simple as a procedural issue, or just something the department / AHJ is used to. The engine/pumper is going to be more than capable of meeting the pressure demand. What type of connection is the fire department / AHJ requesting (LDH, 2.5" Siamese, etc.)? With the limited information provided, it is difficult to fully understand their concerns. Their concern may be charging a single supply line at 217PSI vs multiple supply lines at lower PSI. Seeing such high-pressure requirements may raise a red flag, because it is potentially exposing firefighters on the fireground to the dangers if a failure were to occur. Yes, increasing the standpipe from 4inch to 6inch does not eliminate the pressures exceeding 175PSI. However, it reduces the overall working pressure in the event of a failure. Another concern the local jurisdiction may have is internal obstructions. Depending on the area, a number of factors could introduce foreign objects into the system (rocks, trash, pipe corrosion, etc.). A 6inch standpipe will serve better mitigating those obstructions than a 4inch. Just some thoughts. Best of luck!

Jonathan Joseph

1/25/2023 12:16:07 pm

Since your static is 115, no pressure reducing valves is necessary. To upsize your main feed is pointless unless the "design" needing more flow (GPM) due to your inside hose allowance, calculated friction loss and elevation.

Just curious, how many standpipes are on this system that you would need 217 flowing to reach your 100 psi residual pressure and 250 GPM at your most remote hose valves? There must be a lot of friction in your main to raise this issue to upsizing your main and needing to cause more flow than what the maximum 175psi that is required at the FDC just like Eric stated.

Danefre

1/25/2023 12:27:05 pm

Are you dealing with a partially existing standpipe?

I have yet to run into this with a new system. We always make it work even it means upsizing or splitting the standpipe feed early. Split that 1000gpm early.

At the absolute limit of a manual standpipe you would be losing 35ish psi due to elevation. Not sure if your state defines high rises differently than IBC.

I set up a test calc and with 3 hose valves at 80ft and 1 at 70ft with 1000ft of 6" between them and the demand calc comes in at 149psi at the FDC. Unless you're exceeding these conditions, your problem is the 4". Curious to see your calc.

1/25/2023 03:20:04 pm

Great question and some great responses. Just to add to my previous thoughts, almost all industry standard couplings, pipe, fittings, hose valves, etc. are listed to 300 psi or above. Typically butterfly valves are listed to 250 psi. Technically if the pumper truck CAN pump at 250 psi @750 gpm, and you need 217 psi total @ 750 gpm, then you are correct and technically it should work. But as others have said, usually a small amount of 6" before the split, or even 6" for the horizontal runs will reduce friction loss tremendously. 500 gpm through 5 or 6 floors of 4" pipe isn't that big of a deal. It's when you start shoving 750 gpm or 1000 gpm through 4" that it becomes a problem. Also, make sure you aren't trying to balance the additional hose valves. They should be plugged in as a flat 250 gpm, not as an orifice that is being balanced in the system.

PRVs for Static or Flowing Standpipe Over 175 psi?

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