Expansion Tank End-Of-Line Question

[Jadnashua]

Code calls for domestic water supply systems to be adjusted to NGT 80-psi...so, if yours actually does regularly get to 100, you need a PRV and an expansion tank.

 

[Speede541]

Code calls for domestic water supply systems to be adjusted to NGT 80-psi...so, if yours actually does regularly get to 100, you need a PRV and an expansion tank.

Correct, 105 PSI actually, PRV on the domestic side, and no PRV on the fire side. Expansion tanks on both systems.

I've wondered if there is much variance in our pressure over the course of the day, or seasonally, but whenever I check it pegs right around 105.

 

[Sponsor]

 

[Jeff H Young]

cpvc in my attic for the last 18 years it was 102 here today 75 in oakland

 

[Speede541]

Just to put a bow on this, I received a reply from a "sales engineer" at B&G. It was somewhat unsatisfactory -- he hadn't seen the dead end note previously / wasn't familiar. I suggested Jim's biological assessment to which he didn't disagree. I asked if, for instance, a 2' or 9' stub off of the supply are considered dead ends. Non-committal reply on his part.

For my purpose, I've got no concerns with functionality.

From a DW supply perspective, now I've got all sorts of questions!

 

[Jeff H Young]

The Band G salesman / engineer might not want to tell you that its for something its not aprooved for even though you know its fine. Kind of like using an automotive part on a commercial jetliner, a part thats just as good but half the price why not use it? As far as the Potable water system goes there are standards , codes to adhere to . People install pipe thats imported and unstamped is it just as good? chinnese cast iron drainage pipe some un approoved was a big deal awhile back. Can we run sprinkler pipe for drinking water? if not why not?

 

[Bannerman]

Pressure is exerted equally in every direction so whether the expansion tank is located at the far end of the line, the middle or the beginning, the tank will absorb the volume of expansion occurring in that line. If there are no back-flow devices, pressure regulators or closed isolation valves between risers or branch runs, then a single tank plumbed into one riser can absorb water expansion from all risers and branch lines.

The water within a fire suppression system will not be considered potable as it will not be flushed and replaced on a regular basis but will remain unused for long periods of time and so will become stagnate. As such, the entire fire suppression system will in effect become a dead end. Since it appears no chemicals or additives will be added, a regular expansion tank may be utilized but a clearly labeled or specially colored tank should ensure there is no confusion of the intended purpose for that tank or the pipe feeding it. (Think of a future owner that may want to run water to a refrigerator ice maker)

As you said the expansion tank is to be located in your basement, I anticipate the fire suppression system water also enters through the basement. As such, it would then seem the expansion tank will be Tee'd into the beginning of a riser, not at a dead-end of a riser or horizontal branch line. The line feeding the expansion tank may not be considered a dead-end branch as some amount of water will pass through that line in either direction while the water within the fire suppression system either expands or contracts.

 

[Jeff H Young]

Pressure is exerted equally in every direction so whether the expansion tank is located at the far end of the line, the middle or the beginning, the tank will absorb the volume of expansion occurring in that line. If there are no back-flow devices, pressure regulators or closed isolation valves between risers or branch runs, then a single tank plumbed into one riser can absorb water expansion from all risers and branch lines.

The water within a fire suppression system will not be considered potable as it will not be flushed and replaced on a regular basis but will remain unused for long periods of time and so will become stagnate. As such, the entire fire suppression system will in effect become a dead end. Since it appears no chemicals or additives will be added, a regular expansion tank may be utilized but a clearly labeled or specially colored tank should ensure there is no confusion of the intended purpose for that tank or the pipe feeding it. (Think of a future owner that may want to run water to a refrigerator ice maker)

As you said the expansion tank is to be located in your basement, I anticipate the fire suppression system water also enters through the basement. As such, it would then seem the expansion tank will be Tee'd into the beginning of a riser, not at a dead-end of a riser or horizontal branch line. The line feeding the expansion tank may not be considered a dead-end branch as some amount of water will pass through that line in either direction while the water within the fire suppression system either expands or contracts.

How about an expansion tank aprooved for this work , installed by a qualified sprinkler fitter as per fire department regulations ?

 

[Speede541]

Pressure is exerted equally in every direction so whether the expansion tank is located at the far end of the line, the middle or the beginning, the tank will absorb the volume of expansion occurring in that line. If there are no back-flow devices, pressure regulators or closed isolation valves between risers or branch runs, then a single tank plumbed into one riser can absorb water expansion from all risers and branch lines.

...and that's initially why I questioned this "dead end" directive.

...specially colored tank should ensure there is no confusion of the intended purpose for that tank or the pipe feeding it.

That's one of the reasons I chose the B&G tank, cosmetic -- it's a bright, shiny red. It also transitions from the CPVC to copper less than a foot away, so there'll be no mistaking what it is.

The line feeding the expansion tank may not be considered a dead-end branch as some amount of water will pass through that line in either direction while the water within the fire suppression system either expands or contracts.

See, that's where my mind is at at the moment. Not for my particular fire sprinkler system, that's all settled. But I'm considering the traditional DW installation and the ET "breathing" (albeit slowly) into the flow of clean water. I image the pressure changes are gradual enough that the ET never forcefully "expels" into the supply. I'd also suppose that, on average, over the course of a day, the system pressure tends to be on the low side, i.e. the ET storing the minimum amount of water. But that's got me wondering if mounting the tank above the supply line (inlet facing down) would be superior in that heavier molecules would continually "fall out" and have less of an opportunity to build up, vs. the typical "hanging below" installation which could end up as a collection point.

The thought behind the pass-thru ETs makes sense in theory.

 

[WorthFlorida]

Just to throw in another though. Most homes in Central Florida have backflow preventers, usually at the water meter. On new homes (my home built in 2007), a pressure relief valve is placed at the home entrance. My son's house a pressure relief valve was placed at the water heater by a plumber when the previous owner had the water heater replaced, home built in 1977. A few weeks ago my relief valve was weeping water so I replaced it (WATTS 530C) and the instructions read to set it at 125 PSI or about 25 PSI below the water heater T&P.

WATTS has one approved for fire protection and its PSI is adjustable. I think the only difference is the C has no lead and the FP contains lead. installing one of these, if allowed by local code, would blow off some of the pressure rather than trying to contain it. My though is of the FP system goes to 105 PSI and when it cools down it might drop to only 100 PSI because of backflow preventer. The system can remain too high for comfort with an expansion tank.
https://www.watts.com/products/plum...ressure-only-relief-valves/530c/watts_0371270

 

[Speede541]

That's the blow-off valve I have installed outside on the residential riser.

I ran calcs for 30°F to 140°F and only need capacity for 0.4 gallons of expansion, so the ET ought to cover me.

I figure the ET + blow-off is belt and suspenders.

 

[Jadnashua]

If you precharge the ET properly, under normal system pressure before expansion, there's very little water stored in the tank, so the majority of it is expelled as soon as some is used. In a closed sprinkler system, it would go from being essentially empty early on a cold morning to as full as it would get at the end of the afternoon when the attic has heat soaked during the day. IOW, it does not really 'store' much water unlike a well pressure tank on a normal setup.

 

[Speede541]

If you precharge the ET properly, under normal system pressure before expansion, there's very little water stored in the tank, so the majority of it is expelled as soon as some is used.

Yes! I was surprised when I learned the air bladder fills pretty much the entire volume of these tanks.