Reduce Pressure in High-Rise Buildings?

9/6/2017

A high rise building has pressures of 9 kg/cm^2 (128 psi) at its lowest floor. What does NFPA 13 require in regards to the high pressure or standard industry practice suggest to reduce pressure at the lowest levels? Should an orifice plate be used?

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7 Comments

Darin

9/6/2017 08:12:08 am

I'm getting these emails because I'm studying for the PE test, but I don't know if these are questions designed to help us study or if they are from actual people with actual questions. Please let me know. Thanks.

Joe Meyer link

9/6/2017 08:22:56 am

These are part of the Daily Discussion series we started a couple weeks ago to help answer questions and spur discussion; they are actual questions from actual people.

We've incorporated the Daily Discussions alongside the PE Exam Questions since they are both daily prompts. I didn't want to fill inboxes with two separate emails. That being said, the Daily Discussion Questions are not related to the PE Exam. You can filter only the PE Questions by using the 'Filter By Category' sidebar and selecting 'PE Sample Problems': http://www.meyerfire.com/daily/category/pe-sample-problems

I hope this helps.

Joe

Patrick Turner, P.E.

9/6/2017 08:59:00 am

With regards to the Sprinkler System, most components on a sprinkler system are listed up to 175psi (mainly sprinklers). There are High Pressure Sprinklers available that are listed up to 300psi working pressure. In this case, since pressure at the lowest level is 128psi, your sprinkler systems should be fine and would not need any Pressure Regulating Valves. However, Standpipe Systems are a different animal. If your Standpipe requires a 1.5" Hose Connections, if Residual Pressures exceed 100psi at the required flow then NFPA 14, 2016 Edition Section 7.2.3.1 requires an approved Pressure Regulating Device be provided to reduce the residual pressure to 100psi or less. The Pressure Regulating Device is not required if you have 2.5" Hose Valves or 2.5"x1.5" Reducers at the hose valves (per Section 7.2.3.1.1). Pressure Regulating Devices are only required on 2.5" Hose Valves if the Static Pressure exceed 175psi (per Section 7.2.3.2). Therefore, in your case, if you have 2.5" Hose Valves or 2.5"x1.5" reducers on a 2.5" Hose Valve, no Pressure Regulating Device is required since your Static pressure is less than 175psi. If you have 1.5" Hose Valves then you would need a Pressure Regulating Device to get the residual pressure below 100psi at the required flow at each 1.5" Hose Valve.

I do not know of a Brass Restricting Disc that is UL Listed or FM Approved. Potter Roemer makes a Brass Addjustable Pressure Restricting Device that is UL listed for 2.5" (model 2766 would only be needed if Static Pressure is greater than 175psi). If there are Brass Restricting Discs made by other manufacturers that are UL Listed or FM approved they could be used.

Section 7.2.3.2.1: "Where a listed pressure regulating device is not manufactured, the AHJ shall be permitted to approve a nonlisted device".

However, Potter Roemer does make a 1.5" Pressure Regulating Hose Valve that is listed: Model 4010.

I just used examples of Potter Roemer above, however, there are many other manufacturers of hose valves and pressure regulating devices that might be listed/approved that could be used (Zurn, Watts, Wilkins, Croeker, etc.)

Hope this helps.

-Patrick Turner, P.E.

Darin

9/6/2017 09:04:28 am

Thanks Joe. Regarding the original question, the answer is pretty complicated with a lot of if/then scenarios. Is the 128 psi on the discharge side of an existing fire pump? Of is that city static?
How many stories are we talking? Do you just have one fire pump or is the building tall enough to require multiple pumps in series?
Generally speaking, you will probably want to keep the system under 175 psi (industry standard pressure rating on normal sprinklers, valves, and fittings), so 128 psi is no problem.
If you exceed 175, then you will need to start using pressure regulating valves and/or high pressure fittings, sprinklers, etc. An orifice plate wouldn't help anything and would be a bad idea.
On another note, 128 psi (pump churn including city pressure?) seems really low for a high rise, because you will need 100 psi at full standpipe demand at the highest story.
I realize I didn't really give you any answers. Let me know if I can help you figure this out.

Joe Meyer link

9/6/2017 09:24:38 am

There is a lot to this issue, as you and Patrick have both alluded.

I didn't originate the question (it was submitted to us), but the basic premise I gather is to whether the pressure needs to be reduced on the lowest levels.

As you and Patrick have mentioned, the system should be able to handle 175 psi if the piping and sprinklers, valves, and fittings are listed for the pressure. So to the question, no, reducing the pressure in general or restricting by pressure reducing valves or orifice plates (which may be popular in other parts of the world) is not a recommended means for pressures under 175 psi.

I agree with Patrick that with a high rise, automatic standpipes are likely a requirement so pressures will also likely be higher than 128 psi at the lowest levels.

Joe

David

9/6/2017 09:54:21 am

Both of Darin and Patrick's comments are spot on. There would need to be much discussion on the specific project to verify the actual pressures on the system side.

I would also throw in to coordinate with your AHJ I know of areas that allow up to 200 psi for the 2.5" hose valve before a PRV is required.

9/6/2017 10:17:56 am

Going out on a limb, but I believe that pressure MUST be greater than 128 psi at the lowest floor for a high rise.

Minimum height of high rise is 75 ft = 33 psi to lift that high.

High rise must have automatic or semi-automatic standpipe = 100 psi at top from pump.

100 psi + 33 psi = 133 psi minimum at the lowest floor. Not accounting for friction losses, horizontal piping, safety factor, etc.

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