Concerns for Leaving Dry-Valve as a Wet System?

4/11/2023

What are the physical or regulatory concerns of leaving an older dry pipe valve as wet for an extended amount of time?

This would be during the non-freezing months.

I can think of the alarm trim - water gong changed to electric, clapper gasket integrity, and the inevitable leaks in the overhead system.

Curious on other perspectives, thank you!

9 Comments

Pete H

4/11/2023 06:43:51 am

The immediate problem I can think is this will void the listing of the assembly.

You'll have a pressure switch on a wet system or an alarm valve that's not designed to work with a signal from a flow switch.

Anthony

4/11/2023 07:19:07 am

Well, your system will be under "impairment" because the alarms wort work. the pressure switch on the valve will be constantly going off and that's your means of alerting your alarm system to sprinkler flow. (as Pete mentioned above).

The physical damage of having water present isn't a big concern as most sprinkler components last longer in wet systems as compared to dry systems. Maybe over the long term filling the system with fresh water and draining it every 6months will shorten the life of the pipe with the large volumes of fresh o2. Thus causing more corrosion than usual?

Alex

4/11/2023 07:23:32 am

As others mentioned, you won’t have a means for alarm.

Second, if the system isn’t purged of air when filling (accidental trip) it will lead to corrosion and MIC from trapped air.

Casey Milhorn

4/11/2023 08:07:18 am

I've done it several times (at owners request in writing) and of course need to remove the pressure switch(es) and add a flow switch. I would also highly advise Nitrogen and purge valve, even if its just one of the cheap bottle set ups.

SCHULMAN

4/11/2023 08:14:42 am

Could someone explain WHY you would do this?

Casey Milhorn

4/11/2023 08:32:06 am

Air compressor goes out and/or they are tired of dealing with the maintenance of a dry system (and of course they intend to keep the space heated at a min of 40 degrees). Not my favorite thing to do, and we of course advise they let us install at least a shotgun type wet riser, but it's almost always about the $$$.

The sloping of the pipe doesn't necessarily hurt anything, and the original hydraulics were probably based on 100 C factor and a larger hydraulic area. At the end of the day, a wet system should be more reliable, faster responding, and oversized if the hazard hasn't changed.

As previously stated, I would worry about possible corrosion issues. Maybe consider nitrogen, air vents, etc. to help reduce the chances of corrosion. With the pipe being sloped, there is potential for more than normal trapped amounts of air.

General has a new anti-corrosion system out that is also worth looking into that appears to be more economical than a full nitrogen generator.

Jesse

4/25/2023 10:01:59 am

Wondering the same

Franck

4/11/2023 10:02:06 am

Believe it (or not) but this dual systems were quite common in France about 20 years ago. We called them "Alternative sprinkler systems" as they were alternatively wet or dry.
The reason behind it ? Well, you just need dry system during the winter time, but have a delay for sprinkler activation, and then have the benefit of having a wet system during hot days, so that water is delivered immediately.
These systems had the alarm system on the dry pipe valve (for the dry period) and a flow switch for the wet period. Otherwise, as indicated above, you won't have any alarm when the system is wet.

Was it clever ?
Not really...
The main issue?
Corrosion.
These systems needed to be fully changed regularly (piping and other components).
And if not done, corrosion issues were spectacular, with leakage and sedimentation blocking sprinkler orifices...
We strongly discouraged these installations and asked to keep the systems as a dry pipe system.
If the system is well designed to fight a fire in the winter time, then it is fine to control the same fire under the same conditions during the summer time.

Anthony

4/11/2023 12:27:12 pm

"If the system is well designed to fight a fire in the winter time, then it is fine to control the same fire under the same conditions during the summer time." <- this

Well said, Franck!!

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Concerns for Leaving Dry-Valve as a Wet System?

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