Expansion Tank Volume

[huffdawg]

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.

I guess I meant to say water supply not DHW

 

[huffdawg]

[]

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.


How would it flood the tank? I think there is a bladder inside with the top side charged to 12psi nitrogen. Otherwise there would be no nitrogen in it.

 

[woodsmaster]

Not sure 4 would work either. Need some pressure for the pump.

 

[pwschiller]

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

No, I don't think that there have been. Several of us have recommended checking the pre-charge pressure in your expansion tank bladders. That needs to be done when there is no water pressure pushing on the bladders.

Your system should have been piped in such a way that you can close a valve to shut one or both of the expansion tanks off from the system and then open a second valve to drain the water from the expansion tank(s). Then check the bladder pressure and adjust if needed. This pressure should be equal to the incoming water pressure from your water feed pressure regulator. If the only way you have to drain the water from your expansion tanks in order to check their pre-charge pressure is to drain the entire system, then that was a major piping oversight that should be corrected.

Ideally, you would be able to take one of your two expansion tanks offline at a time, drain the water from it, check/reset the bladder pressure, and then open it up to the system again; all while leaving the other one connected to the system. Then do the same to the other expansion tank.

Once you have checked and re-inflated (if necessary) the pressure in the expansion tanks, make sure that they are both open to the system.

Is your water feed pressure regulator open to the system and do you plan on leaving it open? Is your system currently somewhere around 12 psi?

Then at this point, it doesn't matter if your water temp is at 50°F or 100°F, just heat the system up to temp (190°F?). You should have more than enough expansion capacity for your current system plus the additional storage tank. If that doesn't seem to be the case, then either you 1) haven't set the pre-charge pressure in the expansion tanks properly 2) didn't open them both up to the system 3) have a faulty pressure gauge 4) have grossly underestimated the volume of your system.

In fact, you should have enough expansion capacity that you would only see about a 10-12 psi rise on a 1200 gallon system, if you are starting at 12 psi, and taking the temp from 50°F all the way to 200°F. See the first two charts on this page:http://www.engineeringtoolbox.com/diaphragm-expansion-tank-sizing-d_1272.html

 

[pwschiller]

What Maple1 and I were discussing related to draining some water from the system at say 120°F, in order to bring the pressure back down to 10-12 psi, could be done to reduce your normal operating pressure range, but I wasn't implying that anyone should purposely undersize their expansion capacity. I would use 50-200°F and a max operating pressure of 25 psi when sizing the expansion tanks.

As Maple1 and I both stated, in order to perform this little "trick" to reduce normal operating pressure, it is expected that your water feed pressure regulator (i.e. make-up water) is always open to the system, so it would be impossible for system pressure to drop to low - it can't go any lower than the pressure that your water feed regulator is set to. It also assumes that you don't plan on letting your storage temps get down below that 120°F more than once or twice a year, if at all.

Huff shouldn't need to do this to keep his system pressure in a safe range with the expansion capacity that he has.

 

[huffdawg]

Thanx Peter. I in no way intended to insult anyone if thats the way it seemed . I was getting a little confused.

_ Your right I have not checked the precharge in the two exp.tanks. I read the directions and it says not to adjust initial precharge.
_ My system is piped so I can isolate and bleed down the expansion tanks separately from the system.
_I do not have to drain the whole system to drain my exp. tanks.
_my two exp. tanks are both teed into a 1/2" pex line that goes to the top of my hydraulic separator. where there is three ball valves for bleeding,venting, and
isolation purposes . But I cannot isolate them from each other .( will rectify soon).
_ I feed and regulate the water pressure manually then shut off the valve. when I tie into my house hydronic system It will have a feed and pressure regulator
_The system was taken to 100 °F if I remember correctly then zeroed by draining a little water , pressure then raised to 12psi, then I cracked the valve to the expansion tank. and heated it up to 180 I think and the pressure was 20 psi
_ I plan on keeping my feedwater valve shut for now
_ I think the volume I estimated is very close
_ But I think you might be on to something with the pressure gauge though. I will add another one when I get home
_ when you say 10 to 12 psi rise you mean after the initial 12 psi do you not . so system would hypothetically be 22 to 24 psi @ 190°F

I appreciate everyones input and thank you all very much.

That was a good explanation Peter .Thank You I think I get it now.

 

[maple1]

I'll just add that when my current system was first installed, one of the first things my installer guy did was whip out his pressure guage & check the precharge on my DHW tank. Told me he never trusts factory precharge. Also, I'm not familiar with your expansion tanks, but if they're also commonly used for DHW, DHW precharge is more than 12psi - it would be at least 20, and maybe more. The effect of having a higher precharge would be to reduce the tanks effective acceptance volume. If the precharge was 20, and you heated to 20, there would practically be no expansion available.

And, when you do plumb in your pressure regulator, don't forget a backflow preventer too. Don't want any chance of mixing system water with domestic if your system pressure should rise above your domestic pressure. My system feed valve has always been open, but I'm not sure it really needs to be. The only time it should really be needed is if I spring a big leak - then depending on the circumstances of that, you might want fresh water coming in, or you might not.

However you got there, if you went from 12psi at system rest up to 20psi at 180, sounds to me like you're looking good.

 

[pwschiller]

Thanx Peter. I in no way intended to insult anyone if thats the way it seemed.

You're welcome. I wasn't insulted by you.

I read the directions and it says not to adjust initial precharge.

Yes, they should come set properly, although you could have gotten one that was not.

I feed and regulate the water pressure manually then shut off the valve.

Then you definitely shouldn't try the pressure reducing "trick" that Maple1 and I were discussing.

When you say 10 to 12 psi rise you mean after the initial 12 psi do you not. So the system would hypothetically be 22 to 24 psi @ 190°F

Yes, that was what I meant.

@ http://www.engineeringtoolbox.com/diaphragm-expansion-tank-sizing-d_1272.html: The first graph is assuming an initial temp of 50°F and an initial pressure of 10 psi. If you were at 100°F and 12 psi, that's probably pretty close I would guess. If your system was sized for 50-200°F and a max pressure of 30 psi, then you would have roughly 1.5x the expansion capacity that you need.

The second graph on the page has the following heading: "For initial and maximum pressures different from above - multiply the tank size with the a correction factor estimated from the diagram below". Your "1.5x the expansion capacity that you need" equates to the correction factor on the y-axis of the graph. If you assume an initial pressure (@ 50°F) of 10 psi along the x-axis of the graph, that puts you just below the pink line, which would be a pressure rise of about 10-11 psi. If you assume an initial pressure (@ 50°F) of 12 psi along the x-axis of the graph, that puts you about halfway between the pink and yellow lines, which would be a pressure rise of about 12-13 psi, which should have your overall pressure topping out at around 24-25 psi at 200°F.

 

[huffdawg]

I'll just add that when my current system was first installed, one of the first things my installer guy did was whip out his pressure guage & check the precharge on my DHW tank. Told me he never trusts factory precharge. Also, I'm not familiar with your expansion tanks, but if they're also commonly used for DHW, DHW precharge is more than 12psi - it would be at least 20, and maybe more. The effect of having a higher precharge would be to reduce the tanks effective acceptance volume. If the precharge was 20, and you heated to 20, there would practically be no expansion available.

And, when you do plumb in your pressure regulator, don't forget a backflow preventer too. Don't want any chance of mixing system water with domestic if your system pressure should rise above your domestic pressure. My system feed valve has always been open, but I'm not sure it really needs to be. The only time it should really be needed is if I spring a big leak - then depending on the circumstances of that, you might want fresh water coming in, or you might not.

However you got there, if you went from 12psi at system rest up to 20psi at 180, sounds to me like you're looking good.

Yes my house is plumbed with a backflow preventer and a feed pressure regulator all ready . I will be tee'ing into that system soon and saying adio's to the gas man.

I still have to add another 500 gal tank to the system. I guess 500 more gallons of water to the system will only add another 5psi. or I think I have a defective gauge. You guys got me going in the right direction . I feel more confident that it will be working properly after adding more storage now . I will definately be checking the precharge. Its says precharged to 12 psi on it.

I get back home Weds. ,cant wait to get er dun!

 

[dogwood]

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

HR, is this the Webstone valve you recommend?

http://www.pexsupply.com/Webstone-4...Brass-Ball-Valve-w-Hi-Flow-Hose-Drain-600-WOG

 

[huffdawg]

Installed a couple of glycerin filled pressure guages today. Charged the storage tank up to 180 °F and both of them read 16 psi while the one on the boiler read 22psi. I'd say that the cheap one that came with the boiler is inaccurate.

Huff.