How and Where Does NFPA 20 Limit PRVs?

11/1/2023

Where does NFPA 20's jurisdiction end?

Is it possible to have pressure reducing valves in a suppression system, downstream of a fire pump?

NFPA 20 seems to not allow for that, but does NFPA 20 apply downstream? If so, how far?

In the standard it says up to a last control valve or something like that - what control valve(s) is it referring to?

Thanks in advance.

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6 Comments

Dan Wilder

11/1/2023 08:10:08 am

NFPA 20 (22' Ed referenced) discusses the "discharge valve" or "discharge isolation valve", more specifically in 4.17.8 "A listed indicating gate or butterfly valve shall be installed on the fire protection system side of the pump discharge check valve". The handbook also states in 4.17.11:

"It is important to note that the scope of NFPA 20 stops at the discharge control valve, and nothing in NFPA 20 prohibits the use of pressure-regulating devices downstream of the discharge isolation valve. Any pipe, fitting, valve, or other device downstream of the discharge isolation valve is beyond the scope of NFPA 20, and such pipe, fittings, valves, or other devices should be installed in accordance with the appropriate listing and installation standard, such as NFPA 13 or NFPA 14."

In addition, there is a NFSA EOD question specific to this from August 2006 #1 (Tech Notes) that reinforces the above.

Well worth the money to get the 3 pack of books along with the searchable PDF index!
https://nfsa.org/eodhandbook/

NFPA Link subscription is also well worth the money as it includes both the standards and much of the commentary for quick reference.
https://link.nfpa.org/

James Evans

11/1/2023 08:23:07 am

Another good question is "How far upstream from the pump does NFPA 20 cover?" Since pressure regulating valves are not allowed upstream of a fire pump. In some cases a pressure regulating valve would be beneficial upstream of a fire pump as opposed to downstream.

Dan Wilder

11/1/2023 10:44:28 am

4.16.1 - 4.16.1.1
The suction components shall consist of all pipe, valves, and fittings from the pump suction flange to the connection to the public or private water service main, storage tank, or reservoir, and so forth, that feeds water to the pump.

Glenn Berger

11/1/2023 08:30:46 am

Totally agree with Dan.

To James;s question - Upstream depends on the situation - At times it would be the suction control valve and at times it would be at a point by the connection to the water supply that is installed by others.

Anthony

11/1/2023 08:46:28 am

NFPA 20 explicitly says you can use a PRV downstream of the pump where required.

there are 2 main things NFPA 20 is trying to prevent: 1) Using a 'blow off' relief valve to reduce pressure coming off a pump and effectively dumping water every time a pump is tested or turns on. 2) Using an oversized pump. The pump selected should at some point on the system deliver pressure that is not reduced.

It is not the intent of 20 to prevent al prv's otherwise high rise buildings would require a lot of booster pumps.

See annex section A.4.7.7.2 form NFPA 20:

4.7.7*Maximum Pressure for Centrifugal Pumps.
4.7.7.1 The net pump shutoff (churn) pressure plus the maximum static suction pressure, adjusted for elevation, shall not exceed the pressure for which the system components are rated.4.7.7.2* Pressure relief valves and pressure regulating devices in the fire pump installation shall not be used as a means to meet the requirements of 4.7.7.1.
A.4.7.7.2 It is not the intent of this subsection to restrict the use of pressure reducing valves downstream of the discharge isolation valve for the purpose of meeting the requirements of 4.7.7.

Dusko Nikolic

11/2/2023 04:09:08 am

Thanks for the help. Much appreciated

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How and Where Does NFPA 20 Limit PRVs?

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