Expansion Tank Volume

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huffdawg

Minister of Fire
Oct 3, 2009
1,457
British Columbia Canada
I am just trying to make sure I have enough expansion .this is the results from the amtrol calculator .Are the values I used acceptable. And if there is anyone that can do the math agree with the total.


Total System Volume Gallons 1200
Min Operating Temp 100 f
Max Operating Temp 200 °F
Antifreeze (Glycol) Select 0% (
Min Operating Pressure PSI 12 psi
Max Operating Pressure PSI 25psi



Recommended Models: AX Series: AX-200(V)
L Series: 500-L or a 132 gal.
LBC Series: 500-LBC

I currently have 2 62 gal tanks sx 110's

Huff
 
huffdawg said:
I am just trying to make sure I have enough expansion.
Recommended Models: AX Series: AX-200(V)
L Series: 500-L or a 132 gal.
LBC Series: 500-LBC

I currently have 2 62 gal tanks sx 110's
Huff
The AX-200(V) is a 110 gallon tank with a maximum acceptance volume of 34 gallons.
Each of your SX-110V tanks has a maximum acceptance volume of 34 gallons, so yes you have plenty.

Just make sure the pre-charge pressure of the bladders are set appropriately (12 psig?)
My experience with the expansion tanks on my well water and heating systems is that the bladders do lose their charge over time. When I add on my wood boiler components, I plan on being able to shut off each expansion tank individually from the system with a ball valve and having a boiler drain for each one so that I can relieve enough pressure to check/reset the pre-charge pressure. That would also make it easier to replace an expansion tank if one of them was to fail.
 
Pete Schiller said:
huffdawg said:
I am just trying to make sure I have enough expansion.
Recommended Models: AX Series: AX-200(V)
L Series: 500-L or a 132 gal.
LBC Series: 500-LBC

I currently have 2 62 gal tanks sx 110's
Huff
The AX-200(V) is a 110 gallon tank with a maximum acceptance volume of 34 gallons.
Each of your SX-110V tanks has a maximum acceptance volume of 34 gallons, so yes you have plenty.

Just make sure the pre-charge pressure of the bladders are set appropriately (12 psig?)
My experience with the expansion tanks on my well water and heating systems is that the bladders do lose their charge over time. When I add on my wood boiler components, I plan on being able to shut off each expansion tank individually from the system with a ball valve and having a boiler drain for each one so that I can relieve enough pressure to check/reset the pre-charge pressure. That would also make it easier to replace an expansion tank if one of them was to fail.

Right now with 690 gal. total volume and boiler @ 180 °F the pressure is 20 psi. The expansion tanks came with 12psi precharge. I opened the valve to the expansion tank with 12psi system pressure @ 100 °F . It just seems like if I add my other 500 gal. storage, the system pressure would be to high.

Huff
 
huffdawg said:
I am just trying to make sure I have enough expansion.
Total System Volume Gallons 1200
Min Operating Temp 100 f
Max Operating Temp 200 °F
Antifreeze (Glycol) Select 0% (
Min Operating Pressure PSI 12 psi
Max Operating Pressure PSI 25psi

I currently have 2 62 gal tanks sx 110's

Right now with 690 gal. total volume and boiler @ 180 °F the pressure is 20 psi. The expansion tanks came with 12psi precharge. I opened the valve to the expansion tank with 12psi system pressure @ 100 °F . It just seems like if I add my other 500 gal. storage, the system pressure would be to high.
Huff

You have 132 gallons of tank volume with a theoretical maximum acceptance volume of 68 gallons.
Look at "Diaphragm Expansion Tanks" here: http://www.engineeringtoolbox.com/expansion-tanks-d_885.html

By the graph, your total expansion tank volume should be at least 8% of your system volume = 96 gallons.
and your acceptance volume should be at least 3.8% = 45.6 gallons.
Although the graph is assuming an initial pressure of 10 psig and a max of 30 psig, I think that "Maximum System Temperature" of 200 °F means an average/homogeneous system temp of 200 °F.

Are both expansion tanks open to the system? Other than checking pre-charge bladder pressures (with the expansion tank shut off from the system and water pressure relieved) and verifying the gauge pressure readings, I'm not sure why the pressure would be rising so much. Hopefully someone more experienced than me will chime in if they've got other ideas or my understanding of all this is not correct.
 
My thinking is the min. pressure & temp should be at the min. temp the system would see whether heating or not - eg. room temperature if boiler is shut down in the off season or the fire plain goes out. Does the system really 'operate' down to 100°? Mine is pretty well useless to me below 140. If the numbers are run and system set at 100°/12 psi, then if the system were to drop to say 70°, that would cause the pressure to drop more and it would let more supply water in to get the pressure back up to 12psi. Thereby reducing effective acceptance volume.

Just some quick off the cuff thoughts - did it make sense to anybody else?
 
maple1 said:
My thinking is the min. pressure & temp should be at the min. temp the system would see whether heating or not - eg. room temperature if boiler is shut down in the off season or the fire plain goes out. Does the system really 'operate' down to 100°? Mine is pretty well useless to me below 140. If the numbers are run and system set at 100°/12 psi, then if the system were to drop to say 70°, that would cause the pressure to drop more and it would let more supply water in to get the pressure back up to 12psi. Thereby reducing effective acceptance volume.

Just some quick off the cuff thoughts - did it make sense to anybody else?
Yes. I was planning on doing that with my system when I get it online - draining enough water from the system at say 120-130°F to bring the system pressure back down to 12 psi and figure that the system temp will rarely get below that temp.
 
Both tanks are open right now . Should I be raising the system pressure to 12 psi before opening the valve to the expansion tanks when I put them online. When I put my other 500 gal. storage tank online maybe I will start @ 140 °F .

Thanx for your help guys.

Huff
 
I have a expansion tank that we made from 120 gallon lp tank. I let some water out after everything heated up to lower the psi a little.

So my auto fill will readjust if it cools, that is good to know.

The other issue I have thought about is;

If you have isolation valves for any of your tanks what happens if you close them before the system has cooled?

Much of the expansion water has entered the expansion tank because of the storage volume. My expansion tanks are tied in at the air separator.

Would it draw a vacuum on the storage tank if water can't re-enter because of isolation from the expansion tank?

gg
 
huffdawg said:
I opened the valve to the expansion tank with 12psi system pressure @ 100 °F .
It's not completely clear to me what you mean by this. I assume that you have a feed water pressure regulator, which probably came pre-set to 12-15 psi, or is it set closer to 10 psi? Your feed water is probably coming in at around 55 °F. Are you saying that you heated the water up to 100 °F with no expansion tanks online, at which point the system pressure was 12 psi, then opened the valve(s) to bring the expansion tanks online?

huffdawg said:
Should I be raising the system pressure to 12 psi before opening the valve to the expansion tanks when I put them online.
I'm not sure what advantage there would be in having the expansion tanks shut off from the system initially and then bringing them online after things have heated or filled up.
 
If you have isolation valves for any of your tanks what happens if you close them before the system has cooled?

Much of the expansion water has entered the expansion tank because of the storage volume. My expansion tanks are tied in at the air separator.

Would it draw a vacuum on the storage tank if water can’t re-enter because of isolation from the expansion tank?

Yes. Just when you thought that too much pressure was the greatest problem for a sealed pressurized system comes the opposite scenario.

I've often wondered about those big propane tanks that can take 250PSI. How much vacuum could they take?

Perhaps a vacuum breaker would be a good addition to all the other hardware that goes into these systems? Anyone ever see one on a boiler system?
 
goosegunner said:
If you have isolation valves for any of your tanks what happens if you close them before the system has cooled?

Much of the expansion water has entered the expansion tank because of the storage volume. My expansion tanks are tied in at the air separator.

Would it draw a vacuum on the storage tank if water can't re-enter because of isolation from the expansion tank?

gg

That would probably be bad. I don't think that I want to test out what would happen to my 1000 gallon propane tanks when the water volume is trying to decrease (by say 20 gallons) as the water cools. Even worse would be if your boiler was part of that portion of the system that was shut off from the expansion tanks or water fill inlet.
 
Pete Schiller said:
goosegunner said:
If you have isolation valves for any of your tanks what happens if you close them before the system has cooled?

Much of the expansion water has entered the expansion tank because of the storage volume. My expansion tanks are tied in at the air separator.

Would it draw a vacuum on the storage tank if water can't re-enter because of isolation from the expansion tank?

gg

That would probably be bad. I don't think that I want to test out what would happen to my 1000 gallon propane tanks when the water volume is trying to decrease (by say 20 gallons) as the water cools. Even worse would be if your boiler was part of that portion of the system that was shut off from the expansion tanks or water fill inlet.

So really an expansion tank appropriate for storage volume should be connected to storage itself instead of the diagramed point of no pressure change.

I isolated my tank so I could bypass and run without it if I ever had to, but I would have to let it cool first.

gg
 
goosegunner said:
So really an expansion tank appropriate for storage volume should be connected to storage itself instead of the diagramed point of no pressure change.

I isolated my tank so I could bypass and run without it if I ever had to, but I would have to let it cool first.

gg
Or maybe you could have your expansion tanks tee off to multiple spots in your system - the storage tanks, the boiler piping, your primary loop, etc.
If the piping from the expansion tanks was only 1/2" and it was teeing into say 1-1/4" piping, you wouldn't get much flow going through it under normal circumstances and if each branch from the expansion tanks had its own ball valve, you could shut off individual branches if needed.
 
Pete Schiller said:
goosegunner said:
So really an expansion tank appropriate for storage volume should be connected to storage itself instead of the diagramed point of no pressure change.

I isolated my tank so I could bypass and run without it if I ever had to, but I would have to let it cool first.

gg
Or maybe you could have your expansion tanks tee off to multiple spots in your system - the storage tanks, the boiler piping, your primary loop, etc.
If the piping from the expansion tanks was only 1/2" and it was teeing into say 1-1/4" piping, you wouldn't get much flow going through it under normal circumstances and if each branch from the expansion tanks had its own ball valve, you could shut off individual branches if needed.

Sound like a good idea. Any potential problems with that?

gg
 
goosegunner said:
Pete Schiller said:
goosegunner said:
So really an expansion tank appropriate for storage volume should be connected to storage itself instead of the diagramed point of no pressure change.

I isolated my tank so I could bypass and run without it if I ever had to, but I would have to let it cool first.

gg
Or maybe you could have your expansion tanks tee off to multiple spots in your system - the storage tanks, the boiler piping, your primary loop, etc.
If the piping from the expansion tanks was only 1/2" and it was teeing into say 1-1/4" piping, you wouldn't get much flow going through it under normal circumstances and if each branch from the expansion tanks had its own ball valve, you could shut off individual branches if needed.

Sound like a good idea. Any potential problems with that?

gg
Other than minor flow through the inter-connected expansion piping, I can't think of any.
Maybe a better solution is to just have your big expansion tanks connected to storage and a much smaller expansion tank tied into the rest of the system.
 
I don't think isolation valves are a bad idea but I think I would either remove the handles in the open position and hang them nearby with a piece of wire, etc. Or you could probably zip tie them in the open position. Either way it would take some effort to close them and couldn't be done carelessly. I would only be using them for maintenance when everything is cooled off. I also question the 100 degree minimum like maple1. Even in the off season I think you would want (probably need) to maintain at least 10 psi. So shouldn't we be using 50 for minimum and 210 for maximum? I don't think it would be wise to plan on having to heat up the tank to 100 degrees and then "cut in" the expansion tank. I figured 10% acceptance for expansion but I know it can be done with less providing your calculations and estimations are correct. I'm going to review EW Dudley thread on this.
 
huskers said:
I don't think isolation valves are a bad idea but I think I would either remove the handles in the open position and hang them nearby with a piece of wire, etc. Or you could probably zip tie them in the open position. Either way it would take some effort to close them and couldn't be done carelessly. I would only be using them for maintenance when everything is cooled off. I also question the 100 degree minimum like maple1. Even in the off season I think you would want (probably need) to maintain at least 10 psi. So shouldn't we be using 50 for minimum and 210 for maximum? I don't think it would be wise to plan on having to heat up the tank to 100 degrees and then "cut in" the expansion tank. I figured 10% acceptance for expansion but I know it can be done with less providing your calculations and estimations are correct. I'm going to review EW Dudley thread on this.

Here's the link they referenced. Engineering Toolbox Looks like 4% acceptence is right on for a diaphram tank. A non bladder tank like mine is where they recommend more. Their examples shows 50F for a minimum so I was right about that.
 
huskers said:
I also question the 100 degree minimum like maple1. Even in the off season I think you would want (probably need) to maintain at least 10 psi. So shouldn't we be using 50 for minimum and 210 for maximum?
I think that it depends on how you use your system. For some people there is no off-season; they use their wood boiler and storage year-round for DHW and rarely if ever let the temp get below 130°. It's also assuming the following:
maple1 said:
… if the system were to drop to say 70°, that would cause the pressure to drop more and it would let more supply water in to get the pressure back up to 12psi.
In other words, you have your domestic water supply connected to a pressure regulator which is alway connected to the system to supply make-up water.

If you're someone who frequently lets their storage temp drop well below what is useful, because let's say you travel for work and are away for long periods of time, then you certainly should use 50-70° F for your minimum temp when figuring out your expansion tank requirements.

If you always keep your system within 130-200° F, why not let that temperature swing equate to say a 12-20 psi range instead of a 17-25 psi range?
 
I run the 500 liter Amtrol the OP listed. It is on a 800 gallon system. Fully expanded the pressure is 13 to 13.5 psi. The 500 liter is the minimum tank Atmos recommended, this is a full acceptance bladder tank. There are no problems with either pumping the heating loop or thermosiphening it, Randy
 
Check the pre-charge pressure before you connect them to the system or before you pressurize the system. If you intend to fill the system to 12 psi, then adjust the air charge to that same pressure.

Usually the tanks have a nitrogen charge in them as it does not migrate thru the epdm bladder as fast a O2. Same reason some tire dealers now fill tires with nitrogen, not compressed air. So try not to let more pressure out then you need to.

Webstone does make a nice expansion tank isolation valve with a side port for de-pressurizing.

I would not valve the expansion out of the system even if you bypass the storage tank. Tthe system pressure will rise when the boiler heats and the entire system needs to "see" the expansion tank.

Better to connect the expansion tank into the system at one point only. With multiple connections you have multiple points of no pressure change and the pumps do not have a single reference point. B&G Bell and Gossett wrote a paper about that many years ago.

The tank should be sized for the lowest temperature the boiler will see, usually 50- 55 is the low temperature. If you bring the tank online at 140F you may end up with 0 pressure at 50F. Air vents need some pressure to operate properly same with pumps, always keep at least 5 psi on the system to have a happy, hydronic system.


The fill pressure you chose needs to provide 5 psi at the highest point in the system. If you have more than 2 levels above the boiler/expansion tank you may need a higher fill pressure. 5 psi per level is the rule of thumb .

hr
 
in hot water said:
Check the pre-charge pressure before you connect them to the system or before you pressurize the system. If you intend to fill the system to 12 psi, then adjust the air charge to that same pressure.

Usually the tanks have a nitrogen charge in them as it does not migrate thru the epdm bladder as fast a O2. Same reason some tire dealers now fill tires with nitrogen, not compressed air. So try not to let more pressure out then you need to.

Webstone does make a nice expansion tank isolation valve with a side port for de-pressurizing.

I would not valve the expansion out of the system even if you bypass the storage tank. Tthe system pressure will rise when the boiler heats and the entire system needs to "see" the expansion tank.

Better to connect the expansion tank into the system at one point only. With multiple connections you have multiple points of no pressure change and the pumps do not have a single reference point. B&G Bell and Gossett wrote a paper about that many years ago.

The tank should be sized for the lowest temperature the boiler will see, usually 50- 55 is the low temperature. If you bring the tank online at 140F you may end up with 0 pressure at 50F. Air vents need some pressure to operate properly same with pumps, always keep at least 5 psi on the system to have a happy, hydronic system.


The fill pressure you chose needs to provide 5 psi at the highest point in the system. If you have more than 2 levels above the boiler/expansion tank you may need a higher fill pressure. 5 psi per level is the rule of thumb .



hr

So if I charged the system to 12 psi first then opened the valve to the expansion tank and then heated my tanks up to 25 psi, should I minus 12 psi when reading the pressure guage.
Also the bottom of my expansion tanks are about even with the weld that goes around the endbell of the storage tanks which are vertical . 7-1/2 ft up.

What do mean by levels ? Expansion tank height.

Thanx
 
huffdawg said:
in hot water said:
Check the pre-charge pressure before you connect them to the system or before you pressurize the system. If you intend to fill the system to 12 psi, then adjust the air charge to that same pressure.

Usually the tanks have a nitrogen charge in them as it does not migrate thru the epdm bladder as fast a O2. Same reason some tire dealers now fill tires with nitrogen, not compressed air. So try not to let more pressure out then you need to.

Webstone does make a nice expansion tank isolation valve with a side port for de-pressurizing.

I would not valve the expansion out of the system even if you bypass the storage tank. Tthe system pressure will rise when the boiler heats and the entire system needs to "see" the expansion tank.

Better to connect the expansion tank into the system at one point only. With multiple connections you have multiple points of no pressure change and the pumps do not have a single reference point. B&G Bell and Gossett wrote a paper about that many years ago.

The tank should be sized for the lowest temperature the boiler will see, usually 50- 55 is the low temperature. If you bring the tank online at 140F you may end up with 0 pressure at 50F. Air vents need some pressure to operate properly same with pumps, always keep at least 5 psi on the system to have a happy, hydronic system.


The fill pressure you chose needs to provide 5 psi at the highest point in the system. If you have more than 2 levels above the boiler/expansion tank you may need a higher fill pressure. 5 psi per level is the rule of thumb .



hr

So if I charged the system to 12 psi first then opened the valve to the expansion tank and then heated my tanks up to 25 psi, should I minus 12 psi when reading the pressure guage.
Also the bottom of my expansion tanks are about even with the weld that goes around the endbell of the storage tanks which are vertical . 7-1/2 ft up.

What do mean by levels ? Expansion tank height.

Thanx

I'd guess levels means floors. Two story = two levels.

I'm not sure what you mean by minusing 12psi. Precharge your expansion tank to 12psi of air and empty of water, fill your system to 12psi water pressure (cold, or at minimum temp it would see), then open the valve between your system & expansion. That in theory would lead to no water going into expansion. Heat your water, which would expand the water into the expansion tank and resultingly increase overall system pressure. If you hit 25 psi before you hit your max system temp (200?), you likely need more expansion room. The 25 is a rough guess, I would personally aim for 20 - I've got a thing for higher psi, same as for ladders.
 
[quote author="huffdawg" date="1326990957"]


Total System Volume Gallons 1200
Min Operating Temp 100 f
Max Operating Temp 200 °



Taking 1000 imp. gallons 110F to 195 F = 34 - 36 gallons of expansion in my open ended system.
 

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Seems to be a lot of different plans of attack here.

1) Charge system to what ever you think the lowest usable temp might be. Release pressure to zero then precharge to 12psi . open valve to expansion tanks.

2) Charge system to what ever you think the lowest usable temp might be. release pressure to zero. No pre charge then heat system up

3) Fill system with what ever. temp domestic water might be . precharge to 12 psi open vavle to exp. tank then heat system up.

4) Fill system with what ever. temp domestic water might be. no precharge. open valve to exp. tanks and heat system up.

Are they all ok .

Huff
 
huffdawg said:
Seems to be a lot of different plans of attack here.

1) Charge system to what ever you think the lowest usable temp might be. Release pressure to zero then precharge to 12psi . open valve to expansion tanks.

2) Charge system to what ever you think the lowest usable temp might be. release pressure to zero. No pre charge then heat system up

3) Fill system with what ever. temp domestic water might be . precharge to 12 psi open vavle to exp. tank then heat system up.

4) Fill system with what ever. temp domestic water might be. no precharge. open valve to exp. tanks and heat system up.

Are they all ok .

Huff

Number 1 won't work. the system needs to match the psi in the expansion tank before you open the valve or it will flood the
tank. Correct me if I'm wrong.

Number 2 needs to be lowest system temp not dhw temp.
 
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