Expansion Tank End-Of-Line Question

[Speede541]

I'm installing a second thermal expansion tank. This is for my fire sprinkler system. I'll have 100 feet of 1" copper in my attic, with a storage capacity of about 4 gallons, so am installing a 2 gallon Bell & Gossett PT-5 tank.

The tank will be installed in the basement utility room stubbing of off what could be considered a riser (the sprinkler system is comprised of mostly all 1" line in a looped system; there are four 1" "risers" to the main floor and two to the attic).

Bell & Gossett write that the tank should not be installed at the dead end of a branch, which is precisely where it's going.

I'm trying to figure out the reasoning behind this. As my attic pipes are gradually warmed during the heat of the day, I expect pressure will build steadily across the system, and the expansion tank will serve its purpose.

Similarly, my pressure relief valve, which is located outside at the service entrance just beyond the back flow is effectively the dead end of a branch (assuming no water flow because my house won't be burning).

So any opinions on this edict?

 

[Jeff H Young]

arent all sprinkler lines dead ends? Did they know this is fire sprinkler line?

 

[Sponsor]

 

[Speede541]

The exact verbiage is "Do not install on a dead end pipe or in an overhead joist space."

They also say, "Install ... at a point between the water heater and the back flow preventer, check valve, or pressure reducing valve."

I have an inquiry in to the company asking for clarification.

You're partially correct. The system is a hybrid closed loop / gridded system. Branch systems and trapped air don't make sense (to me) for a mostly CPVC system. So many of my heads are short branches off the loop, some are in line with the loop, and the reason I ended up with four risers into the main floor was to give air an escape path up to one of three purge valves.

But yeah, day to day there's no water flow so technically the whole system is full of dead ends.

FWIW the system is tapped off the the domestic supply made possible by our high water pressure here. It's basically a second domestic supply w/o any additives and w/o any flow.

 

[Jeff H Young]

It sounds like a normal firesprinkler system to me. The sprinklers are not reduced pressure and there is a check valve on it. pressure can only increase. no water ever flowes through your sprinkler lines. The manufacture instructions are not for the fire sprinklers they are for the house. Why would you put an expansion tank on the sprinklers. ?
Honestly Im not a fire sprinkler fitter or qualified to work on them as you arent. Since this tank isnt made for this of cource the instructions will be worthless.
It is interesting but I got more questions than answers sorry. but dont hesitate to share why your messing with this. Id like to learn too. None of the plumbers I know touch fire sprinklers un less they are licsenced

 

[Speede541]

The attic gets hot and so naturally there are daily thermal expansion cycles. More than what's expected from a domestic supply.

I'll be honest, the original permitted installation was a smaller branch system with too many opportunities for entrapped air which is specifically warned against by Spears. No pressure relief valve either.

I understand why fire sprinkler systems get special treatment in the codes and licensing and I'm not going to try to minimize the multiple levels of knowledge, nuance and skill that goes in to a proper system design and installation. I'll only say that I've taken a deep dive into this and am doing this to my own home, under the notion that having fire sprinklers are better than no fire sprinklers.

But back to my original question...

 

[Jadnashua]

If there's a proper check valve between the water going into the sprinkler system and the potable water supply in your home, it shouldn't really matter where the ET is located. In a potable water system, placing it at the dead end would mean water could end up stagnating in the thing. In a sprinkler system, there should be no danger of that stagnant water compromising your potable water unless the check valve failed.

That's my logical thought on it, but I do not know if that is covered in the codes. ETs are designed for heating or potable water situations...sprinklers are sort of a more unique situation.

If there isn't a check valve between the sprinklers and the potable water system, there probably should be.

 

[Speede541]

Thanks Jim, that makes a lot of sense. Yes, I have backflow prevention independently on both systems.

 

[Jeff H Young]

Wouldnt at least part of the question be ? Should this tank be installed in a fire sprinkler system? Yes attics get hot My fire sprinklers in my attic too. Dont know what is unique or what or why youve been working on system. Ok your taking a deep dive ....... but whats the original question?
I think maybe the tank dosent belong in there. if its not on paper I dont think it belongs. No offence but it aint making sence

 

[Jadnashua]

An attic could get to 140-degrees or maybe hotter. That's some fairly significant thermal expansion. Now, the pipe and valves may be able to handle the pressure increase, but the use of an expansion tank should keep the pressure a bit more under control. The check valve should handle it, but excessive pressure might push some of that stagnant water back into the potable system, which doesn't sound like a great idea to me...seals aren't designed for potentially super high pressure caused by thermal expansion.

 

[Jeff H Young]

So something is special about his house compared to the other millions of houses. oakland is on the san fransisco bay . 25 degrees cooler than where I live Ive never seen a tank on a resedential sprinkler house. Are they the norm in cool citys? Also Jadnashua he mentioned nothing about a hot attic or any of what you just said. I gotta say Jad it makes some sence what you say but Ive never heard of adding a tank. have you? So Im just asking why install something that isnt desighned for it ? Id say its a good chance the tank isnt legal ? maybe someone thats done this can explain

 

[Themp]

Quick internet search had this first:

https://www.amtrol.com/product/fire-x-trol-expansion-tanks/

 

[Jadnashua]

A sprinkler system is a closed system, just like a water heater is when there's a check valve or a pressure reduction valve in the system...you could easily have the same pressure differential between night and day in the attic where the sprinkler lines are as you'd have in a water heater. It doesn't take much at all to peak the pressure enough to open the WH's T&P valve, which should open at 150psi. THere's nothing in a sprinkler system to release excess pressure unless you add an expansion tank. Now, a dry system wouldn't have that issue, as the air is much more easily compressed...water doesn't compress!

I had never looked into one for a sprinkler, but it doesn't surprise me that they make them! Good catch...

One for potable water or a heating system would likely work, too unless you're using antifreeze in the lines...then, it may need a different bladder material.

 

[Jeff H Young]

like that. aprooved for fire sprinklers

 

[Jeff H Young]

any expansion tank would likely work . Im sure one made for plumbing will save you money. rather than putting the correct one in.

 

[Speede541]

Hey Jim your theory looks spot on.

B&G hasn't replied to my inquiry (I'll share their response if they do), but I located discussions about Legionella and microbes specific to dead end tank branches, and even found "flow through" expansion tanks made specifically to address this concern.

https://www.calefactio.com/en/product/flow-through/

I'll have to remember not to plumb a drinking fountain off of my fire sprinkler line!

 

[Jeff H Young]

Hey Jim your theory looks spot on.

B&G hasn't replied to my inquiry (I'll share their response I'd they do), but I located discussions about Legionella and microbes specific to dead end tank branches, and even found "flow through" expansion tanks made specifically to address this concern.

https://www.calefactio.com/en/product/flow-through/

I'll have to remember not to plumb a drinking fountain off of my fire sprinkler line!

So in other words an un knowlegeable home owner messing with the fire sprinklers could actualy cause an un healthy situation right?.

 

[Jadnashua]

Hopefully, a sprinkler system (at least a wet one) will never see any flow...so, you really need a quality valve designed to isolate the system but reliably open when it might be needed. Being then closed, and not needed for potable water, any expansion tank should help manage the overall pressure based on thermal expansion issues. If the system may have antifreeze in it, you'd want an ET suitable for that as well.

The actual volume in a sprinkler system isn't often huge, but might still benefit from an ET.

Typical piping used for a sprinkler system tends to be rigid, so won't balloon, so any expansion raises the pressure radically.

 

[Speede541]

Thanks Jim!

It's CPVC on the lower floors and transitions to copper in the attic., and a 20' PEX run inside of one interior wall. I've never had the warm 'n fuzzies for CPVC, but that's what the original layout was. Although I have a pressure regulator on the domestic side, the Fire Marshall approved this system based on our >100 PSI service, w/no PRV.

Some of the CPVC runs through heated joist bays in the basement ceiling.

The 100 feet of copper in the attic store about 4 gallons of water, and need about 1/2 gallon of expansion capacity between my min and max temperatures.

The check valve is a NIBCO unit. I'm not sure if it was part of the off-the-shelf residential riser that was installed, but it was approved as part of the submittal to the city.

In any case, the high pressure off the street combined with my CPVC concerns made me want to make sure I've got over-pressure protection (with a pressure blow-off valve outside on the riser). A tech who performed an annual suggested I flow the water quarterly, and I've been mostly sticking with that, exercising the check valve in the process.

And yeah, no anti-freeze.

 

[wwhitney]

Typical piping used for a sprinkler system tends to be rigid, so won't balloon, so any expansion raises the pressure radically.

In a SFR, it's typically CPVC or PEX these days.

Cheers, Wayne

 

[Speede541]

I'm a fan of the PEX systems from what I've seen so far. They weren't approved yet when this system first went in. And CPVC in the attic struck me as too risky, hence the copper.