Air separator and steel expansion tank connection

[700renegade]

I need some advice - my boiler setup right now has a Taco Vortech air seperator with it's stock hy-vent built in and a small bladder hydronic expansion tank hanging off the bottom. I haven't hooked up my storage but plan to do so this fall.

I'm installing two 1000 gal vertical LP tanks and directly above the boiler room on the mezzanine I'll be putting a vertical 250 gal LP tank to act as my expansion tank.

Originally I planned to connect the bottom of the expansion with a 1/2" pex to about any random spot in the system thinking it didn't matter.

n reading the instructions for the Vortech though, I see it says "If using a plain steel expansion tank, you can direct connect a 3/4" line to the top ( in place of the Hy-Vent ). The pitch up to the tank can not be less than 1" in 5' and not exceed 7 feet total length. if the distance is more than 7 feet, increase pipe size to 1" "

What advantage would there be to connect my expansion tank in place of the vent, and why would they ask for such large dia lines? It will take hours to bring my storage from 110* to 190* - a 1/2" pipe should be plenty to accomodate the movement of 100 gal of water into the expansion tank in that time.

 

[ewdudley]

Some of the old non-bladder expansion tanks set in the floor joists above the boiler used to have a fitting that would use a separate line to take air from the air separator and run it up a tube inside the tank above the water in the tank and the water connection would come from elsewhere. I know of one such installation that ran without needing any makeup water or air for over 50 years.

Sounds like Taco has figured out a way to do it with one tube as long as it goes up hill and is fat enough not to hold a big bubble that the water runs underneath of. I would think you could run small separate lines, one for air to the top and one for water to the bottom if it was convenient and you wanted a sure thing.

 

[700renegade]

Thanks for turning the bulb on. In the case of the Hy-Vent the air bubble is discharged from system pressure ( say 20 psi ) to atmosphere. If I plumb it to the tank it doesn't have that 20 psi to drive it up the tube. I can see how a bubble could stay stationary in that line if it was small diameter.

I my case once the system is bled there would rarely be bubble,s and they'd get flushed upwards when the water expands when the boiler is running.

Why would there be a need to bring a second tube to the top of the expansion tank? any air bubble would just burp up to the top of the water in the expansion tank.

What advantage would there be in piping it this way vs. just leaving the Hy-Vent in place?

 

[ewdudley]

Thanks for turning the bulb on. In the case of the Hy-Vent the air bubble is discharged from system pressure ( say 20 psi ) to atmosphere. If I plumb it to the tank it doesn't have that 20 psi to drive it up the tube. I can see how a bubble could stay stationary in that line if it was small diameter.

I my case once the system is bled there would rarely be bubble,s and they'd get flushed upwards when the water expands when the boiler is running.

Why would there be a need to bring a second tube to the top of the expansion tank? any air bubble would just burp up to the top of the water in the expansion tank.

What advantage would there be in piping it this way vs. just leaving the Hy-Vent in place?

Only if running two small pipes is easier than one 1" pipe (if 1" is what you need for gas bubble reasons).

Also there is supposedly an efficiency advantage running the expansion water from a colder point than the air separator, but even for 2000 gallons you're only looking at maybe 40-50 gallons of maybe 120 degF water vs 185 degF so probably not worth going after unless it's convenient.

In theory the cooling expansion tank water will dissolve gas and return it to the system and then as the water is heated by the boiler the same gas will come out of solution and will go back to the expansion tank (or to atmosphere if the separator is vented). However the guys with non-bladder propane tank expansion tanks who simply vent their air separators generally report no problems with gas loss. ([Edit: See below, looks like it may be more of a problem than I thought.) With an elevated non-bladder expansion tank you have an opportunity to be more sure there won't be problem.

[Edit:] It might make sense to return cool expansion tank outlet flow to the bottom of the system where it will remain cooler until reheated by the next cycle. This way dissolved gases are more likely to stay dissolved, which might not be the case if expansion tank outlet flows directly to the top of storage where it would be re-heated and would tend to lose dissolved gas.

If you really want to put a bow on it, elevate the expansion tank above the top of the storage tanks and run a line from top of storage to top of expansion.

 

[heaterman]

B & G Air Trol is what you are looking for...

http://www.pexsupply.com/pex/control/search/~SEARCH_STRING=air trol

 

[700renegade]

I think the Air-Trol are set up for horizontal expansion tanks, not sure how they'd work for a 250 gal tank stood on end. The top of my expansion tank will be close to the top of the 16' LP tanks, but not higher.

At this point I'm still thinking leave the Hy-Vent in the air separator on the hot outlet of the boiler, and run a 1/2" pex line from the bottom of my LP tanks ( where the water will be coldest ) to the bottom of the expansion tank. I may have to drain water or add air to the top of the expansion tank occasionally if needed to balance the system.

I'll need to research ideas for a cheap sight gauge for the side of the expansion tank so I can monitor whats happening in there. Need transparent pex I guess.

 

[goosegunner]

I have a non bladder expansion tank. It is situated on the floor of the boiler room. I think air does get into the system somehow because I have had to add air a few times in 2 years. At some point I am going to get bladder tanks and use my current 120 gallon tank for a buffer tank near my DHW and forced air furnace.

gg

 

[ewdudley]

I'll need to research ideas for a cheap sight gauge for the side of the expansion tank so I can monitor whats happening in there. Need transparent pex I guess.

Plain old oxygen barrier PEX should be plenty translucent enough. Or spritz bottle and a hair dryer works pretty good if you don't mind futzing with field expedients.

 

[woodsmaster]

I have a bladder less tank on the floor and have to add air occasionally. If I had the auto fill hooked up I think it would waterlog. Sometime soon I'm going to raise it up to about the top of my vertical storage and add a line from the air separator to the tank. If I still lose air I will change to a bladder tank. I will let you Know how it works. Might work on it this week.

 

[700renegade]

What about this solution:

I can put a waste connector on the air vent of the Hy-Vent on the Vortech air scoop and run a small 1/4" diameter line up to my expansion tank. this will burp any air that gets removed into the expansion and hopefully limit adding makeup air.

I'll also run a 1/2" pex off the bottom of my 2000 gal storage and connect that to the bottom of the expansion tank so that the coldest water ( 120* ?? ) in my system is transported to/from the expansion tank. I estimate roughly 40 gallons will make the round trip each time the storage tanks go thru a full heat cycle. This will limit the radiant losses I'll get off the un-insulated expansion tank up in my storage mezzanine ( its inside the heated shop so it's really not 'lost' btu's ).

I could connect expansion to the discharge from my in-floor system ( 60*-ish ), but if I didn't pay attention I could screw up and accidentally isolate the storage from the expansion if I turned valves the wrong way. If I could find a cheap 5 psi poppet relief valve, I could tee the storage into the expansion feed also, so the connection to the in-floor was primary, but the storage could push past the relief valve and see the expansion tank before the 30psi blowoff kicks in.

Does anyone see a problem with the Hy-Vent seeing system pressure instead of atmosphere on it's air discharge? Assuming the water connection to the expansion is near the suction side of my boiler pump ( my pump is located on the bottom inlet to the boiler after the mix valve ) and the air vent is on the hot top side of the boiler, the only pressure differential the vent will see is that created by the circulation pump ( a few psi when running ). Normally the vent sees 12 to 30 psi when vented to atmosphere.

 

[ewdudley]

I'm pretty sure you'd want to remove the Hy-Vent from the Vortech and plumb the air riser straight into the Vortech.

I could connect expansion to the discharge from my in-floor system ( 60*-ish ), but if I didn't pay attention I could screw up and accidentally isolate the storage from the expansion if I turned valves the wrong way. If I could find a cheap 5 psi poppet relief valve, I could tee the storage into the expansion feed also, so the connection

They definitely advise against creating opportunities to isolate the expansion vessel. But the idea makes sense, and you could save maybe fifteen or twenty thousand BTUs per burn cycle, although it just seems pretty elaborate.

 

[700renegade]

OK - I think I'm going to plumb my primary line to the expansion tank from the return manifold off my in-floor shop loop ( it returns about 60* water ). In addition I'll install one of these inexpensive brass check valves that have a low cracking pressure from my 2000 gal of storage to the expansion tank also:
http://www.surpluscenter.com/Water-Pumps/Water-Valves/Other-Valves/1-2-BRASS-CHECK-VALVE.axd

This should limit the opportunities for me to do something stupid with a valve and isolate the expansion tank.

I assume I'd need to install a pair of these facing opposite directions to allow water to flow both ways. Cracking pressure is a bit lower than I'd like - It could be low enough to cause some ghost flow issues in certain situations.