Relief Valve for Wet Pipe Sprinkler Systems?

5/3/2019

NFPA 13 (2016 Section 7.1.2 or 2019 Section 30.3.1) requires a relief valve on all wet pipe systems. The only exemption is where air reservoirs are installed to absorb pressure increases, then a relief valve isn't required.

This seems straightforward but I don't recall seeing independent relief valves on the far majority of the wet pipe systems I've come across. How is this requirement typically met from a design standpoint? Am I missing something or looking in the wrong place?

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9 Comments

Wayne Ammons

5/3/2019 06:54:19 am

Prior to the 2010 edition of NFPA 13, only gridded wet pipe systems were required to have this relief valve. Tree systems typically have more trapped air than gridded but with air venting becoming more popular for mitigating corrosion (also required with the 2016 edition of NFPA 13), there should be less trapped air in all wet pipe systems. This can cause increased pressures within the system due to water fluctuations, solar heating, etc.

I typically include the relief valve on the inspector's test on the riser. You can buy an inspector's test and drain assembly (i.e. AGF) or piece it together with individual components.

Jim McHugh link

6/4/2019 11:55:59 am

Hi Wayne,
Prior to 2010 you also needed to install a relief valve downstream of all pressure reducing valves. One of the issues is code recommend 1/2" valves in one area and 1/4" in another.
This was cleaned up in the 2010 edition.
Thank for mentioning our AGF TESTanDRAIN valves. Our models 1011A and 2511A included a UL/FM pressure relief valve and drainage piping.
Thanks, Jim McHugh

TJ Jones III

5/3/2019 10:16:39 am

Your Ready Risers can come with a Relief valve on the Test and Drain. You can also order them in an assortment of settings. 175 PSI is the standard for them so you have to plug them during testing.

Franck

5/3/2019 10:23:57 am

As indicated above, this is quite a new requirement (less than 10 years) and is not retroactive. So many systems are installed without this piece of equipment.
But it is not a bad requirement. Not only for possible air trapped in the system (and corrosion issues) as indicated by Wayne, but also for possible pressure built-up in some systems.
Some sprinkler systems are regulated at quite a high pressure. And the pressure downstream the ACV remains at a high level, whatever the possible fluctuations on the pressure upstream on the water supply side.
If the building has high difference of temperature between day and night (heated by the sun under the roof, for example) or for systems running close to hot equipment, the pressure might increase even more (this is a closed system and a fluid that is heated will expand) and could reach very high levels, sometimes up to 175-200+ psi... which is not good for long term operations on sprinkler systems (sprinkler heads are normally rated at 175 psi).
This is when this pressure relief valve is interesting, even for old systems.

Ivonn

5/3/2019 10:29:30 am

Relief Valve are require in a wet system agree with section 8.1.2 NFPA 13 Ed.2019 in each system except where have an air reservoirs like you said, typically the inspector, test and drain have a 1/2" relief valve and you comply with that point.

StephenJ

5/3/2019 11:18:13 am

I just wanted to point out that the requirement you pointed out are different. Section 30.3.1 in the 2019 version of NFPA 13 is a requirement specific to merchant vessel systems. Chapter 30 is titled marine systems.

Section 7.1.2 in the 2016 version is now 8.1.2 in the 2019 version. The intent of 8.1.2.1 is to prevent pressure in wet pipe systems from exceeding 175 psi for sprinkler systems or the maximum working pressure. You would have to use a little judgment here and evaluate the supply to determine the likelihood of exceeding this pressure.

David Toshio Williams, PE/FPE link

5/6/2019 11:24:57 am

Before this change in the Code we were the A/E firm on a project fairly near a city water system pump station, the pressure pulsations from the pump station would gradually build in the sprinkler system until the heads would blow. In the end the system check valve was drilled with a small hole to relieve pressure (and the City checked how it was operating their pumps). (Back in the day we only provided a single check valve on the water service connection).

Today we would have called for the installation of the relief valve and that would have taken care of this issue.

I have seen more than one "new" installation where the relief valve has been skipped even if we show it in the design details we call for in a performance design project. I think the trades are still learning about this 10 years later!

The test connection with 3/4 inch relief valve tapping seems to be the way to go.

Jon Paton

5/17/2020 10:22:28 pm

My system was poorly designed. Static fire water pressure is constantly at or above the relief valve rating. This causes the valves to constantly leak. I can't rebuild the fire system. Can I put two valves in parallel or in series to reduce pressure? Would that invalidate the system?

Thank you

Jim McHugh link

5/18/2020 07:39:42 am

Hi Jon,
You can get different pressure ratings on the pressure relief valves. The pressure marked on the valve indicates an operating range. An example would be a 175 PSI valve begins opening at 90% of its range so it would begin opening at 158 psi. Also the valves are designed to be fully closed once the pressure drops below 80% of it indicated range or 140 psi. You may need to simply swap out the valve you have for a different pressure such as 205 psi or 225 psi. If you have other technical questions please give me a call at 610-240-4900 Thanks Jim McHugh

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