Pressure Problems

[Armaton]

SX-90 has 34 gallons of acceptance, if I remember correctly the rule of thumb is 10% of system volume, (but can get away with down to 5% sometimes) with your tank and associated lines you should have close to 600 gallons which puts you at barely enough at the low side. Would think you need more expansion.

 

[nbroyer]

I also suspect more expansion is needed - but you have to check your precharge pressure first to find where you're at now or else it's just a guess. Then settle on a system temp & pressure number for depleted storage as a starting point. I would assume at least 190 for upper temp for sizing purposes. And no more than 20psi for upper pressure.

How did you come up with selecting the SX90? Did you use a tank sizing app? I just checked a couple of them and the 90 is borderline for 600 gallons depending on how you fiddle with the parameters. Eg., changing upper temp to 190 from 180 took the selection from a 90 to a 110 tank in one case. And you should use caution with the parameters - err on the side of safety.

It is a very good idea to have multiple guages in the system - they can be inaccurate. I think I have 6 or 7 on mine. Should also consider where all those guages are height wise in the system when you're reading them. Every 10' of water height = 4psi.

The expansion tank came with the wood boiler and storage tank when I bought it used. I thought I had read people were using this same tank with 1000 gallons of storage, so I assumed it was safe.

I will check the precharge pressure in the expansion tank when it cools down and go from there.

Thank you for all the help so far!

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[nbroyer]

My storage tank is at 135 degrees right now and the pressure is 12 psi. I measured the psi on the expansion tank and it is 15 psi.

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[maple1]

So, if you let your system drop to the lowest temperature it would usually see (maybe 110-120°?), then get your system pressure set to where you would want it then (maybe 10psi?), then check the air pressure in your expansion tank and set it to the same (10psi) - you should get the expansion tank to the point that it will be doing the most it can for you. Which still may not be enough - you will find out when you heat the system back up. Looks like your precharge is 15psi - which I would consider a few pounds too much.

(Numbers are rough guidelines only. All based on where you are measuring things and other variables. The absolute least amount of system pressure that I would want to see in my system, is one that will still keep a couple psi's at the top of the system, when the system goes absolutely stone cold (60°?) over the summer months. E.g. if your system is 20' tall top to bottom, that equates to around 10psi at the very bottom. If it is 10' tall, that would be 6psi).

**DISCLAIMER - I am not a pro.

 

[Fred61]

I read a lot of stuff in several discussions that I don't understand and normally comment if I think I have some knowledge on the subject. This pressure/expansion subject arises quite often and it has me baffled.

Could someone explain to me what's happening when you have a bladder expansion tank with 10 psi on the air side why you wouldn't have the same 10 psi on the water side assuming the bladder has the same area on each side. (hydraulics). I can understand overpressure from the supply bottoming out the bladder or under pressurized lower than the initial precharge.

 

[maple1]

I read a lot of stuff in several discussions that I don't understand and normally comment if I think I have some knowledge on the subject. This pressure/expansion subject arises quite often and it has me baffled.

Could someone explain to me what's happening when you have a bladder expansion tank with 10 psi on the air side why you wouldn't have the same 10 psi on the water side assuming the bladder has the same area on each side. (hydraulics). I can understand overpressure from the supply bottoming out the bladder or under pressurized lower than the initial precharge.

In the above 15psi air/12psi system example, there is 15 psi of air in the bladder tank and the bladder is fully expanded, since there is less than 15 on the system/water side. The air has pushed all the water out. The bladder won't move - or expansion won't accept any expansion - until system pressure goes more than 15psi & overcomes the 15psi on the air side. Then it will start pushing the bladder in.

Did that help?

 

[dogwood]

Nbroyer, I've a thousand gallons of storage. I initially used online expansion calculators to figure out I needed 57 gallons of acceptance to give me the expansion needed, plus a little extra. I purchased an Extrol SX 160 (46 gallons acceptance) plus a SX 30 (11.3 gallons acceptance) providing a total of 57.3 gallons of acceptance. I was at the time, leery of not having enough acceptance, as I'd seen pictures on site of individuals using two SX 160's for a thousand gallons storage. But I trusted the calculations and figured I'd save some money.

Needless to say, I ran into the exact same problem as you. I did check the tanks pre-charge air pressure beforehand though, which was 12 psi, as I recall. At the time, I quickly bled off a little water from the system as a temporary fix (which I added back later). I decided not be be cheap again, and bought and added a second SX-160, like the others I'd seen had for their 1000 gallon storage. That solved the problem immediately. So now I've a total of 103.3 gallons of acceptance with the two SX 160's, p[lus having left the SX 30 in the system. My storage at this moment is just shy of 180 degrees and the pressure gauge is reading about 15-16 psi, which is pretty typical.

At 500 gallons you have half the total volume of storage, so I'm guessing you'd be successful with the equivalent of only one SX 160 (46 gallons acceptance). You're probable a bit light on acceptance volume at 34 gallons judging from my bad initial, overly optimistic calculations. If you get up to about 46 gallons acceptance I'd bet you be okay. Good luck,

Mike

 

[nbroyer]

So, if you let your system drop to the lowest temperature it would usually see (maybe 110-120°?), then get your system pressure set to where you would want it then (maybe 10psi?), then check the air pressure in your expansion tank and set it to the same (10psi) - you should get the expansion tank to the point that it will be doing the most it can for you. Which still may not be enough - you will find out when you heat the system back up. Looks like your precharge is 15psi - which I would consider a few pounds too much.

(Numbers are rough guidelines only. All based on where you are measuring things and other variables. The absolute least amount of system pressure that I would want to see in my system, is one that will still keep a couple psi's at the top of the system, when the system goes absolutely stone cold (60°?) over the summer months. E.g. if your system is 20' tall top to bottom, that equates to around 10psi at the very bottom. If it is 10' tall, that would be 6psi).

**DISCLAIMER - I am not a pro.

Thanks for the advice, maple. I tried this this morning where I set the pressure at 110 degrees to 10 psi in both the expansion tank and the system. The wood boiler is now up to 180 degrees and the storage tank is 165 degrees at the top and the system pressure is already up to 21 psi. At the main loop, when the house calls for heat, it's up to 24 psi. So I guess this means I can't squeeze enough out of my existing expansion tank and need an additional one.

Nbroyer, I've a thousand gallons of storage. I initially used online expansion calculators to figure out I needed 57 gallons of acceptance to give me the expansion needed, plus a little extra. I purchased an Extrol SX 160 (46 gallons acceptance) plus a SX 30 (11.3 gallons acceptance) providing a total of 57.3 gallons of acceptance. I was at the time, leery of not having enough acceptance, as I'd seen pictures on site of individuals using two SX 160's for a thousand gallons storage. But I trusted the calculations and figured I'd save some money.

Needless to say, I ran into the exact same problem as you. I did check the tanks pre-charge air pressure beforehand though, which was 12 psi, as I recall. At the time, I quickly bled off a little water from the system as a temporary fix (which I added back later). I decided not be be cheap again, and bought and added a second SX-160, like the others I'd seen had for their 1000 gallon storage. That solved the problem immediately. So now I've a total of 103.3 gallons of acceptance with the two SX 160's, p[lus having left the SX 30 in the system. My storage at this moment is just shy of 180 degrees and the pressure gauge is reading about 15-16 psi, which is pretty typical.

At 500 gallons you have half the total volume of storage, so I'm guessing you'd be successful with the equivalent of only one SX 160 (46 gallons acceptance). You're probable a bit light on acceptance volume at 34 gallons judging from my bad initial, overly optimistic calculations. If you get up to about 46 gallons acceptance I'd bet you be okay. Good luck,

Mike

Based off of your experience, Mike, I am looking at the Extrol SX-30V, SX-40V, or SX-60V which all have 11.3 gallons of max acceptance. This would give me a total of 45.3 gallons of acceptance. Does this seem more reasonable? The next step up would be another SX-90V like I have, giving me 68 gallons of acceptance, but at $200 more than the others. I'm not against spending the money if necessary, but if the smaller tanks will work for me, I'd rather do that. What does the additional tank size gain me with the same max acceptance between the 30, 40 and 60?

Thanks for everything so far everyone. I really appreciate it and I've learned a lot.

 

[dogwood]

What does the additional tank size gain me with the same max acceptance between the 30, 40 and 60?

That's a good question nbroyer. I have no idea. You might contact Amtrol at 1-888-757-4774 between 8am – 5:45pm to to get an answer to this question. Their site advertises at that number you can "speak with a real person who will go out of their way to help!". If they do have the answer, please post what it is. Thanks. Maybe they'll even do a calculation for you if you call.

I think they have an expansion calculator on their site if you want to do it yourself. You might try it and see what kind of results you get. Not that whatever one I used back then yielded useful results.

Mike

 

[maple1]

Thanks for the advice, maple. I tried this this morning where I set the pressure at 110 degrees to 10 psi in both the expansion tank and the system. The wood boiler is now up to 180 degrees and the storage tank is 165 degrees at the top and the system pressure is already up to 21 psi. At the main loop, when the house calls for heat, it's up to 24 psi. So I guess this means I can't squeeze enough out of my existing expansion tank and need an additional one.



Based off of your experience, Mike, I am looking at the Extrol SX-30V, SX-40V, or SX-60V which all have 11.3 gallons of max acceptance. This would give me a total of 45.3 gallons of acceptance. Does this seem more reasonable? The next step up would be another SX-90V like I have, giving me 68 gallons of acceptance, but at $200 more than the others. I'm not against spending the money if necessary, but if the smaller tanks will work for me, I'd rather do that. What does the additional tank size gain me with the same max acceptance between the 30, 40 and 60?

Thanks for everything so far everyone. I really appreciate it and I've learned a lot.

Based on your last posted pressures I think I would go with another 90. 165 at the top isn't near charged and you're already close to max pressure. If that 165 doesn't go all the way to the bottom you'd be almost sure to be needing more than 30% more expansion than you already have. The peace of mind would be worth it IMO. Once you get over the $200 extra.

 

[salecker]

I had a chance to climb up to my expansion tanks yesterday to see what i have.
My tanks are Extrol, big tank is a 110,which wasn't quite enough without juggling the pressure and water in the boiler every year.I added the 30 that came with my boiler and everything has been fine the last few years.
I don't know if it matters but my tanks are up high,the bottom of the expansion tanks are about 6" above the top of my storage tanks.

 

[nbroyer]

I was ready to buy another sx-90v today but called Amtrol first to talk with their customer support (thanks for the idea, Mike!). They swore the one tank really should work, but if I wanted to buy one to just get the smaller sx-30v. They said the larger tank volumes with the same max acceptance are used if your system runs on higher pressures like commercial buildings.

Anyways, before I took the plunge, I decided to drain out my expansion tank first and reset it back to 12 psi and try one more fire. I actually ended up having over 20 gallons of water in it at the cooler temperature where I expected not to have much at all. I must have messed this up when I let out some air when the system pressure was getting too high. The other thing I thought is maybe the initial pressure was really low when I filled the system so a lot of water filled the expansion tank right off. It would make sense because the guy I bought it from had to drain it out to sell it to me.

The good news is I got the storage tank to 180 degrees today and the system pressure only got to 19 psi! On the main loop when the house called for heat, its pressure got to 22 psi. I think I can live with this, but know I can always add another tank later on if I feel like it.

Thanks for all the help and advice everyone!

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[maple1]

I'm not understanding some of what you wrote there. How did you drain water out of the tank? If you let that much water out of your system, that was only 10psi when you last set your air pressure the same, then your cold pressure will drop out to way below that next time it cools that much.

 

[nbroyer]

I'm not understanding some of what you wrote there. How did you drain water out of the tank? If you let that much water out of your system, that was only 10psi when you last set your air pressure the same, then your cold pressure will drop out to way below that next time it cools that much.

I have an isolation ball valve above the expansion tank. I shut that and released all of the air. Then I disconnected the tank at a union. Then I slowly added some air back in to the tank to push out water (wish I had a drain at the base). I emptied the water in to a 5 gallon bucket which helped me see how much was in the tank. Once it was empty, I added enough air until it was set to 12 psi and then reconnected it to the system. I opened the isolation valve and then added in more water until the system pressure was also 12 psi. Hopefully this was the right way to do things and not mess up anything.

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[maple1]

Depending what your air & system pressures were before you did that, all the water you drained out might have come back in when you reset system to 12. Also think results would have been the same by just letting water out of the system at a convenient drain point until system pressure drops below air side pressure by a couple pounds or so. Might have had to add a bit of air to air side to get it there. With the expansion tank hooked to the system, the air side is pushing water out of the water side whenever the air pressure is higher than system pressure. Until there is no water left in the tank and bladder is fully expanded.

You should carefully watch system pressures the next time your storage goes cold.

 

[nbroyer]

Depending what your air & system pressures were before you did that, all the water you drained out might have come back in when you reset system to 12. Also think results would have been the same by just letting water out of the system at a convenient drain point until system pressure drops below air side pressure by a couple pounds or so. Might have had to add a bit of air to air side to get it there. With the expansion tank hooked to the system, the air side is pushing water out of the water side whenever the air pressure is higher than system pressure. Until there is no water left in the tank and bladder is fully expanded.

You should carefully watch system pressures the next time your storage goes cold.

You may be right. I wanted a clean baseline to know exactly what the pressure was in the expansion tank. The system pressure was down to 10 psi when I removed the tank. I am definitely keeping a close eye on everything still.

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[maple1]

Do you know what your tank temps were at the time?

 

[nbroyer]

Do you know what your tank temps were at the time?

The top of the tank was 130 degrees, bottom was 120.

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[dogwood]

You should carefully watch system pressures the next time your storage goes cold.

Nbroyer, you said when you drained some water, and reset your expansion tanks air pressure, your tank was 130 degrees at the top, and 120 degrees at the bottom, At that temperature, you have boiler water that has expanded quite a bit already. When your system is shut down for the off season, when the water cools and the storage tank gets to its lowest temperature, you might have the problem of way too little or negative pressure, and whatever might come from that. I'm not sure what would happen to your system then, but wouldn't want to find out. Maybe only air would get sucked in through the auto air vents, I don't know. So like Maple1 says, watch your system pressures when your system goes cold.

You should reset your system's psi when it's water is at it's coldest probable off season temp, let's say 50 degrees. If the highest temp you can achieve is 180 degrees, then you allow for how much your 500+ gallons of water will expand in volume going from 50 to 180 degrees = 130 degrees. In practice, if your system is filled to its proper psi at it's coolest temp, you will know if you have enough expansion volume the first time you heat the system up the full 130 degrees. Right now, because of the draining, you don't know if you have the right amount of water in your system. With too little water in your system, it might only appear you have enough expansion. I temporarily drained some water off to get that effect.

When I knew I had insufficient expansion and needed another expansion tank, I let the system cool down as close to 50 degrees as it would go. Then starting at my system preset of 15 psi, I added the new expansion tank. If you don't have auto fill and a pressure regulator valve, that's when you would add or subtract water yourself to get to whatever your system's startup psi is. Then I fired the system up to 180 degree to see if I now had enough expansion to keep the psi no more than 20 which is what I was shooting for. You could do the same to figure out if you needed an extra tank or not.

Mike

 

[nbroyer]

Nbroyer, you said when you drained some water, and reset your expansion tanks air pressure, your tank was 130 degrees at the top, and 120 degrees at the bottom, At that temperature, you have boiler water that has expanded quite a bit already. When your system is shut down for the off season, when the water cools and the storage tank gets to its lowest temperature, you might have the problem of way too little or negative pressure, and whatever might come from that. I'm not sure what would happen to your system then, but wouldn't want to find out. Maybe only air would get sucked in through the auto air vents, I don't know. So like Maple1 says, watch your system pressures when your system goes cold.

You should reset your system's psi when it's water is at it's coldest probable off season temp, let's say 50 degrees. If the highest temp you can achieve is 180 degrees, then you allow for how much your 500+ gallons of water will expand in volume going from 50 to 180 degrees = 130 degrees. In practice, if your system is filled to its proper psi at it's coolest temp, you will know if you have enough expansion volume the first time you heat the system up the full 130 degrees. Right now, because of the draining, you don't know if you have the right amount of water in your system. With too little water in your system, it might only appear you have enough expansion. I temporarily drained some water off to get that effect.

When I knew I had insufficient expansion and needed another expansion tank, I let the system cool down as close to 50 degrees as it would go. Then starting at my system preset of 15 psi, I added the new expansion tank. If you don't have auto fill and a pressure regulator valve, that's when you would add or subtract water yourself to get to whatever your system's startup psi is. Then I fired the system up to 180 degree to see if I now had enough expansion to keep the psi no more than 20 which is what I was shooting for. You could do the same to figure out if you needed an extra tank or not.

Mike

Mike,

I'm trying to understand this. Since I completely drained the expansion tank, but no water out of the rest of the system, reset the air pressure in the tank and then hooked it back up and added enough water to get the system pressure back to 12 psi all while most of the system water was still around 130 degrees, wouldn't the worst case scenario be what Maple suggested where the amount of water I just dumped out got added back in? I can definitely see how doing this at 130 degrees could be a problem now and I will be watching the pressure as the temperature goes below that. I also just plugged in some numbers into a water expansion calculator to see how much water should have been in the expansion tank at 130 degrees, if it was 600 gallons at 50 degrees initially, and it should only have been about 7 gallons, not over 20 like I had. I know that I definitely messed things up by releasing air when the system was hot, among other things.

 

[maple1]

Trying for basic physics:

I had to google some to refresh my long-gone memory from school days, but I think that 600 gallons of water will increase in volume by 20-22 gallons or so, going from 50° to 190°.

https://www.engineeringtoolbox.com/volumetric-temperature-expansion-d_315.html

If you start with an empty expansion tank at 12psi of air, and double that pressure to 24psi by halving it's volume via introduction of that amount of water, that = a 40-44 gallon expansion tank. (Boyles law > 2x air volume reduction = 2x air pressure increase. I think.). The 90v tank is a 44 gallon tank. Which is right at the limit. But that is assuming max psi of 24. Which would be above my comfort level. I would much prefer a max pressure of 18psi. Which would require 66 gallons of expansion. Which would mean adding an SX40 which is 20 gallons.

That also kind of fits with the old ballpark estimation of aiming for 10% expansion volume for system volume.

Been a long time since I crunched things like that, I might have messed up somewhere....

 

[dogwood]

Nbroyer, I'm no expert on hydronics by any stretch. I'm relating to you my experience from having to solve the same problem you're experiencing.

You stated "I added enough water to get the system pressure back to 12 psi while the system water was still around 130 degrees". In my estimation, you should let your system cool down to your low design temperature, before adding water back to reset the psi. The low design temperature is the lowest temperature storage might possibly get to, most likely seen in the off season when you're not burning.

My understanding is the amount of acceptance volume you have in your expansion tanks has to be enough to be able to absorb the maximum amount of expansion that can occur. That amount encompasses the water volume at the system's likely lowest possible temperature and it's likely highest temp. I chose what I thought was a conservative value of 50 degrees as my low design temp and 180 degrees as my high design temp. 180 degrees is the the maximum temperature my Tarm Solo Innova will heat storage to.

A low temp of 50 degrees and a high temp of 180 degrees establishes 130 degrees as the maximum range of temperature my system may see through both the heating and off season. In order to keep the system psi no higher than desired, my expansion tanks have to to provide enough acceptance to accommodate how much the systems 1000+ gallons of water will expand when heated 130 degrees The first burn of the heating season may likely raise your storage temp that much in just a few hours.

In your case, you reset your psi when your system temp was already up to 120-130 degrees. So you'll only be seeing at most 60 degrees worth of expansion when you heat your tank from 120 to 180 degrees, or whatever your highest storage temp might be. As a consequence, you are now temporarily getting away with having considerably less acceptance volume than your system requires, and not blowing water out your pressure release valve.

Things won't go south for you until your storage gets below 120 degrees, the temp at which you set your psi, That is why you now need to carefully monitor your system as Maple 1 indicated. You don't want it to get below that 120 degree temp before you have added some more acceptance volume with a new expansion tank, and then properly reset your pressure when your systems cools down to your low design temp, Then you won't have to concern yourself about it anymore.

I didn't want to put off solving my own excessive psi problem. You might as well solve yours now, because your temp is going to drop below 120 soon as you stop burning, when the heating season ends. Once my second SX 160 arrived I did the following. I let the system cool down by using up whatever remaining usable heat there was in storage. I heated our home with our propane furnace for a few days, while storage continued to cool down to as close to as I could get to the low design temp of 50 degrees. At that point I plumbed in the second Extrol SX 160, reset the system to 15 psi, fired up the boiler, and returned storage to 180 degrees.

At storage rose towards 180 degrees I monitored the pressure gauges. I happily observed that the system pressure remained well below 20 psi, right up to storage reaching 180 degrees. I was assured this problem was permanently solved. The two SX 160's together, together with the SX 30 I left plumbed in, had accommodated my 1000+ gallons of water's maximum amount of expansion when heated a full 130 degrees. It wasn't a big hassle to accomplish, other than paying the cost of that new tank.

Mike

 

[dogwood]

Nbroyer, how is this working out for you?

 

[nbroyer]

Nbroyer, How is this working out for you?

I didn't make a fire for a couple of days and the storage tank got down to about 110 degrees. At that temperature, the system pressure was 8 psi. I'm going to get through this season keeping the storage above 130 degrees and add another expansion tank next summer.

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