over pressure problem with storage

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eriesigtau

Member
Jun 15, 2010
75
Titusville, PA
My system is going up to 28#'s of pressure when I heat up the storage and the circ's are on. I have 2 expansion tanks. One is an Extrol SX-90 which suposidly has 44 gal of volume. The other is a #90 which has about 14 gal of volume. Together I should have 58gal for expansion. I have radient floor heat, 2 radiators, 500 gal of storage and an econoburn 150. I'm gonna guess I have about 600 gallons in the system. Any ideas why the expansion tanks are not doing their job? They are factory set at 12psi and the system is set at 12psi when cold and circ's are off. Is the pipe size going to the expansion tank critical? Does air below the bladder need to be purged? I just piped the tanks into the system and fired it up.
 
Did you check the pressure on the expansion tanks? Factory presets still need to be verified. My tanks came with a little extra air in them.

You certainly should be fine with 58 gallons of expansion. Do you trust the pressure gauge that is indicating 28psi? Have more than one? Can you fell the warm water moving into your expansion tanks during a heating cycle?
 
Are the numbers you refer to total volume or acceptance volume? I just installed a very similar (Biomass 40) system and I needed one 30 and two 90s. I think the 90s are 11 gallons acceptance volume each.

If your water was very cold when you set the pressure, maybe it expanded over the designed amount? I set my system to be 14#, when hot, in a three floor house. No problems so far......

Good luck,

Bill
 
I didnt know the tank pressure needs to be set when hot. Anyone else agree? Between the SX-90 and the #90 there is 45 gal of acceptance volume. I have 2 guages within the system and both read the same.
 
Tank pressures DO NOT need to be set when the system is hot. Tanks need to be set separate from the system. Being, the isolation valve between the tanks and the system are closed. A Tee with a drain valve should be between the tank and isolation. The drain should then be opened and the tank will be at atmosphere. Now the bladder pressure can be accurately read with NO influence from the system. Your charge should be a few PSI less than your intended system pressure. This will then allow transfer to and from the tank without raising and lowering your system pressure from expansion and contraction of the heating and cooling of liquid that cannot be compressed.
 
I reduced the pressure on the SX-90 2#'s and she is currently heating up. So far it hasnt budged by we got a little ways to go. With all circ's on it goes from 12 to 20. ill keep you updated.
 
I am watching your thread closely, keep us updated. My new system is up and running. So far, not to much change in pressure. A little increase when I brought the storage tank up to 160. I am watching everything closely. Luckily I have the next two days off. Boiler is running nice. Good luck and have fun.
 
eriesigtau said:
I reduced the pressure on the SX-90 2#'s and she is currently heating up. So far it hasnt budged by we got a little ways to go. With all circ's on it goes from 12 to 20. ill keep you updated.

Did you take both tanks to atmosphere and check your charges in the bladders? When you set the feed reg up, its nice to have a valve downstreem with a guage upstream of that. Its a quicker way to find out exactly what it stops feeding at.
 
Okay, I spoke to soon. When my tank come up to 170 and my boiler was up to 175 my pressure came up at wood boiler from 15 psi to 18 psi. Not bad. But then I checked pressure at oil boiler. Pressure there was about 15 psi. Now that is up to 25. Is that something I need to worry about? I doesn't sound to bad, the system will probably not be much higher than those temperatures. How are you making out Eriesigtau?
 
Well, I checked it this morning... I am at 22lbs and everything is charged to about 185deg... the circs are not on though because there is no call for heat this morning. I did not put the expansion at atmosphere. I would need to cut valves in to do that. I just took 2lbs off the SX-90. Gotta go to work, ill check when I get home.
 
Gasifier said:
Okay, I spoke to soon. When my tank come up to 170 and my boiler was up to 175 my pressure came up at wood boiler from 15 psi to 18 psi. Not bad. But then I checked pressure at oil boiler. Pressure there was about 15 psi. Now that is up to 25. Is that something I need to worry about? I doesn't sound to bad, the system will probably not be much higher than those temperatures. How are you making out Eriesigtau?

Are you saying that your oil boiler was at 25 when your wood was at 18? Shouldn't they all be under the same pressure? Or maybe I misunderstood.
 
Bladder pressure tanks normally come precharged at 12 psi. You can check that with a pressure gauge on the fitting of the tank before the tank is installed, of if installed, isolate and drain the tank, then check. This charge normally is good for a 2 story house with the tank in the basement because it will lift water to about 27' and keep the system pressurized when it is shut down and cold. You want the system fully pressurized at all times to keep air out of the system. Otherwise when the system cools down it will pull air into the system, and that will result in corrosion until the added O2 is consumed, and this may repeat each year or several times/year.

With the tank pressure set on a cold system, then the pressure will rise as the water heats. Maximum pressure of 22-25 psi on a hot system is usually OK, but higher than that can cause some pressure relief valves to start to weep, even though they are 30 psi valves. If the pressure relief valve weeps or drips as temperature rises, the system needs more acceptance volume from its bladder tanks. Add another bladder tank. When calculating the gallons of water the pressure tanks must accept, I use 4% of total system water, some use 5%. Most tank suppliers have a calculation chart on their websites to aid in determining which tank or how many tanks you need.

If you have experienced the pressure valve weeping or dripping and that has occurred for any substantial period of time, the valve may need to be replaced. Weeping and dripping can cause mineral deposits on the valve seat which will not allow it to seal tightly and the valve will continue to weep/drip at pressures below 30 psi when it should be holding tightly.
 
Eriesigtau,

Certainly don't want to steel your thread. Just going through the same thing you are at the same time. Thought it would be okay and we both might learn something from each others experience. Hope you don't mind man. Tell me to shut the hell up if you do. You won't hurt my feelings. ;-)

Are you saying that your oil boiler was at 25 when your wood was at 18? Shouldn’t they all be under the same pressure? Or maybe I misunderstood.

Keeping an eye it. Oil boiler pressure is reading about 22 or 23. Wood boiler pressure is reading 18. They are in two seperate rooms. Wood boiler, storage and three expansion tanks in one room. (One for the boiler and two for the storage tank.) On the other side of hallway is oil boiler room. One expansion tank for that there. Pipes go up and over the hallway between the two rooms and run between floor joist over the hallway. I don't know if they would or should both even out with this system or not. I am not worried about them being even. Just don't want any of it to go to high of course. Is 22 or 23 okay to leave at. Before wood boiler I believe the PSI on oil boiler was about 15-17. What do you guys think?
 
Gasifier said:
Eriesigtau,

Certainly don't want to steel your thread. Just going through the same thing you are at the same time. Thought it would be okay and we both might learn something from each others experience. Hope you don't mind man. Tell me to shut the hell up if you do. You won't hurt my feelings. ;-)

Are you saying that your oil boiler was at 25 when your wood was at 18? Shouldn’t they all be under the same pressure? Or maybe I misunderstood.

Keeping an eye it. Oil boiler pressure is reading about 22 or 23. Wood boiler pressure is reading 18. They are in two seperate rooms. Wood boiler, storage and three expansion tanks in one room. (One for the boiler and two for the storage tank.) On the other side of hallway is oil boiler room. One expansion tank for that there. Pipes go up and over the hallway between the two rooms and run between floor joist over the hallway. I don't know if they would or should both even out with this system or not. I am not worried about them being even. Just don't want any of it to go to high of course. Is 22 or 23 okay to leave at. Before wood boiler I believe the PSI on oil boiler was about 15-17. What do you guys think?


Do you have a heat exchanger between the two systems or do they share same water?

Also, do you guys have auto fill valves connected to domestic water?

gg
 
Do you have a heat exchanger between the two systems or do they share same water?
Also, do you guys have auto fill valves connected to domestic water?
gg


For my system I do not have a heat exchanger between them, all one system sharing the same water. Baseboard throughout house, in floor radiant in concrete garage floor.
Yes, I believe I have an auto fill valve in my system. Once they had the new pipes hook up to the old ones all they had to do was open a ball valve to fill the other side. Took a while to fill that 400 gallon tank. :coolsmile:
 
I'm having a hard time understanding why the pressures would be that different in two places in the same system - shouldn't the whole system read the same?

I thought my pressure regulator thingy (hope I didn't get too technical there) was acting up a couple of years ago, because I noticed that the guage was reading about 20 rather than the usual 12 or so. I bought a new guage, and before I started ripping things apart too much to change the thingy, I just ripped them apart enough to plumb the new guage in as a second guage - along with putting a couple more ball valves in to make that section easier to service. 12psi - the old one still said 20. So guages can go wonky over time.
 
I’m having a hard time understanding why the pressures would be that different in two places in the same system - shouldn’t the whole system read the same?

I thought my pressure regulator thingy (hope I didn’t get too technical there) was acting up a couple of years ago, because I noticed that the guage was reading about 20 rather than the usual 12 or so. I bought a new guage, and before I started ripping things apart too much to change the thingy, I just ripped them apart enough to plumb the new guage in as a second guage - along with putting a couple more ball valves in to make that section easier to service. 12psi - the old one still said 20. So guages can go wonky over time.


I do not know why it would be different in two places in the same system. Seems like the whole system should read the same. I was wondering if it is because the expansion tank for the oil boiler is small, enough for the 30 gallons or so in that boiler. But up and over the walls and into the wood boiler room is 400 gallons in the storage tank and 60 gallons in the Wood Gun. Have I possible created a little to much pressure with the storage and wood boiler both up to 170 °F and the pressure has settled over by the oil boiler where the smaller expansion tank is? I do not know? Maybe someone does. Suggestions anyone? And. Is it even a problem? I would rather see the pressure at both guages back under 20psi. But is it a problem if the actual pressure is 23psi at the oil boiler and 17-18 at the wood boiler?

That is a very good point about the old and new guages. The guage on the oil boiler is about 7 1/2 years old. Wood boiler guage is brand new. But, the temperature seems to read just fine. Two different needles/guages. But it seem to work by going from what it was to what it is now. I love seeing the temperature of the oil boiler down to 100 degrees now because it has not turned on in more than a day. :coolgrin:
 
My bad guage was also a guage with the two needles - the temp part seemed to still be working, the pressure one seemed to gain 20 pounds for some reason (there must be a wife joke there somewhere, but I won't go there...). First I was thinking it got dirt in it, but from another experience I think that would lead to a low reading. The second one I put in is solely a pressure guage. Could there be a check valve or backflow preventer in the system between the two guages? Then again there would have to be two checks or blocks in the system to get two different pressures - in my mind anyway. This is quite interesting, I'm trying to get my head around what I'm planning for next year here, it's seeming like storage & expansion might end up being the harder and maybe more $$$ part of the whole thing.
 
Ok, here is the newest update. Right before I left for work I checked it one more time and the main circ came back on. The pressure stayed constant at 22 at full temp. I can honestly say that this is the first time since I installed this system last year that I havent had a problem when using the storage. I am a happy camper! I came home from work and everything was idle and the house is nice and warm (4000 sq ft). I felt under the storage tank insulation and I could barely keep my hand on the metal at the bottom of the tank (10hrs after I shut the boiler down) The system is now at 15psi. Once the weather breaks here later this week, I will cut a valve and drain in so I can check the expansion tank atmospheric pressure.

For those who wondered why I had 2 gauges, I didnt trust the one so I piped in another just to check but they were both the same. If people use 6% for a rule of thumb then my SX-90 should be able to handle the entire system without the #90. Doesnt hurt to have it though.

Now if I could just find a way to get my boiler gassing quicker, I would be set. Seems like it takes 3hrs of burning before I get a good enough coal bed where it "really" gasses.
 
Not sure this is the thread for it, but I'd like to see what everyone is using for expansion - I've been gleaning bits & pieces here & there, but my head starts to swim from reading all the different threads on here. I guess I should start taking notes.
 
jebatty said:
When calculating the gallons of water the pressure tanks must accept, I use 4% of total system water, some use 5%. Most tank suppliers have a calculation chart on their websites to aid in determining which tank or how many tanks you need.

When choosing a bladder type expansion tank it is important to keep in mind the difference between 'acceptance volume' and 'tank volume'.

For a bladder tank, acceptance volume is the amount of water that can enter the tank without exceeding the capacity of the diaphragm. Four percent of system volume is enough acceptance volume to accommodate a system whose temperature stays inside the range of 40 degF to 210 degF.

Different size tanks can have the same acceptance volume because they share the same diaphragm subassembly, but of course they're not interchangeable just because that have the same acceptance volume.

Having enough acceptance volume is necessary, but not sufficient. The total tank volume needs to be large enough so the pressure doesn't go too high once the tank accepts the acceptance volume. For a system that goes from 12 psig to 30 psig when the temperature goes from 40 degF to 210 degF the tank volume needs to be 10.5 percent of total system volume, but they are plenty of installations that are using the 86 gallon Amtrol tank for 1000 gallon systems with no problem because the temperature range is more like 60 degF to 190 degF.

--ewd
 
This is sort of on topic so I'll ask it here: what are the pros & cons of bladder vs. non-bladder? $$$ vs. $$$? Performance? My current tank is non-bladder.
 
eriesigtau said:
Now if I could just find a way to get my boiler gassing quicker, I would be set. Seems like it takes 3hrs of burning before I get a good enough coal bed where it "really" gasses.

The trick is to shut the boiler down when there is a good layer of coals remaining.

A good way to do this is to use a stack temperature sensor to shut off the draft fan when the stack temperature get below 280 degF to 300 degF. Without air the coals go black.

Then to start the fire level out the charcoal, turn on the draft fan with a timer, hit the charcoal with a propane torch for just four or five seconds with air drawing down through the nozzle, pile on the dry fuel tight and flat, and walk away. As the charcoal ignites the unit will gasify inside of a minute or two.
 
maple1 said:
This is sort of on topic so I'll ask it here: what are the pros & cons of bladder vs. non-bladder? $$$ vs. $$$? Performance? My current tank is non-bladder.

I believe theoretically gas can dissolve into the expansion tank water as the system cools and then it has the opportunity to come out of solution when hot water from the boiler passes through the air separator, or perhaps some can migrate to high points in the system. So eventually the expansion tank loses gas and has to be re-charged.

I say in theory because this doesn't seem to be such a big problem with guys that use non-bladder tanks. And even if it was going on, you could re-charge with nitrogen and side-step the problem.

The conventional non-bladder systems often had circuitry for reclaiming air separator gas back to the (elevated) expansion tank. My neighbor tells me his system of this type needed no recharging from 1962 to 2009, when he replaced his boiler.

Bladder means less to worry about, generally take up less space, and they're easier to set up.

Both are very much valid choices.
 
Maybe I've been doing this wrong - I was going off fuzzy memories of what my installation guy ran by me real quick years ago at installation time - fixing a waterlogged tank? But, whenever I noticed the pressure creeping up a few pounds in my system, I would close the valve going to my expansion tank (tied up in the floor joists above my furnace), then open the drain valve on the bottom of the other end of it and let all the water out of it (also opened a bleed screw on the top). After the water was all out, I'd close those two valves again and open the valve back up to my sytem. I did all that cold - it returned the tank to atmosphere. The system lowered back down a few pounds and all was good again. I haven't done that for a while now, it seems to be pretty steady - but I haven't fired it up to heating temp yet this year. Was that procedure out to lunch? Maybe I should save up some questions & start another thread - but any chance the guys having problems in this thread have a leaky bladder? I know domestic water tanks can have that problem if you get a bad one.
 
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