Auxiliary Drain Required to be Bottom of Pipe?

10/30/2023

Can an auxiliary drain for a dry system be mounted on the side of pipe?

We've debated it recently after finding a situation where the auxiliary drains were mounted on the side of the pipe. I've been unable to find proper documentation concerning the orientation for the auxiliary drain.

I did find the 5-gallon rule for wet systems, however, I was unable to find a specific reference for a dry system.

Thanks in advance!

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4 Comments

Dan Wilder

10/30/2023 08:07:33 am

13-22'
16.10.5.3.3 for <5 Gal
16.10.5.3.5 for >5 Gal

As for how it's tied into the pipe, if coming out the side does not create a trapped section within the pipe (typically a size on size or possibly an eccentric fitting), then the intent is met. Could an argument be made for a 1¼" pipe with a 1" outlet out the side or maybe a 2½" off a 3", possibly (depends on creativity of the argument at that point), There is no specific orientation or point of attachment of a drain that I remember....it falls back to piping it so that the drain works (I'd lean towards common sense but that likely provides too much interpretation).

If the approach is taken similar to the "Air Venting", then the intent is to remove as much trapped water within the system from a single point. The only difference is an Aux Drain location is well defined per 16.10.5.1 "...where a change in piping direction prevents drainage of system piping through the main drain."

Casey Milhorn

10/30/2023 10:08:09 am

See below for sections from NFPA 13, 2016 ed.

8.16.2 Drainage.
8.16.2.1* General. All sprinkler pipe and fittings shall be installed so that the system can be drained
8.16.2.3 Dry Pipe and Preaction Systems. Piping shall be
pitched to drain as stated in 8.16.2.3.1 through 8.16.2.3.3.
8.16.2.5.3.3 Where the capacity of trapped sections of pipe is
less than 5 gal (20 L), the auxiliary drain shall consist of a valve
not smaller than 1⁄2 in. (15 mm) and a plug or a nipple and
cap.

The intent (in my opinion) is to ensure ALL sections of dry systems are able to be drained by way of valve (including the belly of the pipe). BUT, doesn't say that directly. probably worth a TIA submittal to NFPA on this since there is room for interpretation. Great question!

RYAN HINSON

10/30/2023 10:34:17 am

It is my opinion that complete drainage required per NFPA 13 (2022) Section 16.10, can only be achieved where the drain comes off the bottom of the lowest portion of the trapped system section.

For the same reason flush-seal gaskets are required on dry and preaction systems prevent trapped water in the undrainable sections of the gasket, we want to drain all water from the inside of the piping. A drain out the side of a main could leave substantial amounts of water inside this the pipe section which are capable of cracking fittings upon freezing (common in MN).

What is the point of pitching the piping as required per Sections 16.10.3 only to allow the low point drains per Section 16.10.5 to pool because the drain orientation off this low-point is not at the 'low-point'? In larger mains, 5 gallons could easily be surpassed just in the trapped 'haunch' of the pipe below such an ill-advised drain orientation/placement.

I'd also point to the allowable PENDENT configuration of the sprinkler for a <5 gal trapped section for wet-pipe and preaction systems in areas not subject to freezing in lieu of a valved drain as indicated in Section 16.10.5.2.3(2).

While not explicitly stated, I believe all these sections/considerations infer/assume that the auxiliary drain is out the bottom of- or eccentric to- the low-point location allowing for full drainage so that drain pipes are "...arranged to avoid exposing any of the water-filled portion of the sprinkler system to freezing conditions" per Section 16.10.6.6.

I personally, do not even allow roll-grooving of piping in such systems as this creates small pooling locations within the pipe which prevent full drainage of pitched pipe...not to mention the corrosion potential created.

Anthony

10/30/2023 01:14:11 pm

There is no specific provision requiring a drain be at the bottom of the pipe. However, it is strongly implied throughout NFPA 13 with phrases such as "completely drained." I would also sy its industry best practice.

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Auxiliary Drain Required to be Bottom of Pipe?

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