She canna take any more, Cap'n! She's gonna blow!
Homeowner here. Apologies to Scotty.
So this heating season I've noticed a somewhat alarming situation. During prolonged boiler firing (typically after the nightly setback) I've seen the PSI creep just north of 30. The PRV has not opened up, but I am concerned that it might.
Thoughts on the following would be appreciated.
My thought is to do a combination of the following:
- reduce system pressure (lower initial system pressure)
- decrease level of water in the compression tank (more air)
- replace underused radiator with much smaller one
- Inject air in underused radiator (to serve as secondary compression tank)
- Turn off the ODR "boost mode"
Here's the rundown: This morning I observed the following:
- System supply:
- 32 PSI
- 140F
- Boiler supply:
- 31 PSI
- 170F
- Boiler return:
- 30 PSI
- 140F
- Circulator:
- 8.5 ft / head
- 11 GPM
- Zones:
- 2 of 3 calling for heat
- ODR
- Outside temp 43F
- Setpoint 170F (this is because the ODR is configured ("boost mode") to raise the setpoint by 20F every 30 minutes when the system is continually calling for heat. Initial setpoint 140F).
- Compression tank
- 24 gallons
- 27 PSI
- Water level set using Aitrol ATF-12
See pictures below. There are:
- 9 free-standing radiators (initial system had 10, 1 was removed)
- XX feet of 9" CI baseboard (added to initial system)
- XX feet of 7" CI baseboard (added to initial system)
System Supply when cool:
- 70 F
- 13 PSI
Thanks,
Eric
System Supply
Boiler Supply
Boiler Return
System Supply (Cool)
Comments
-
show us your expansion / compression tank, and how it's piped to the boiler,
it needs service
known to beat dead horses
5 -
either a tank up in the ceiling, or a small, 5 ish gallon tank hanging from the pipes around the boiler
known to beat dead horses0 -
Start with just lowering the cold pressure. 10 psi is 23'. If you have a 2 story house, that's plenty.
When it gets warmer, check your PRV. It may need replacement. Note, it may start leaking after the test, so be ready.
What did it run at previous years?
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.0 -
On the road - will post follow up later.
Compression tank installed per B&G instructions from Aitlrtrol and pitched up with 1” pipe. Water level set per instructions. Pics to follow.
—Eric
0 -
how and where are you reading 27 psi on the compression tank ?
known to beat dead horses0 -
I also have a gauge installed on the bottom fitting of the tank.
Eric
0 -
the system pressure needs to be at zero before reading pressure
0 -
I think it's a ceiling tank, compression, not expansion hanger
known to beat dead horses
1 -
Yep. Has an Airtrol.
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.0 -
still want to see how we're reading 27psi,
and is that 27 hot or cold at boiler ?
known to beat dead horses0 -
did you drain the ceiling tank?
0 -
Compression tank is waterlogged. It's not hard to fix that problem… maybe… Close the valve on the pipe from the system to the compression tank. Find the drain on the tank and open it. AND WAIT for all the water to drain out. This may take a while… you can speed it up though, sometimes, if you can run a small pipe into the drain and up to the top of the tank so air can get in. Then close the drain and reopen the valve from the system to the tank. Add enough water to the system to bring the system pressure to 12 pisg.
No valve between the tank and the system? Or no tank drain? Oh dear… may have to drain the system to allow all the water out of the tank.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England2 -
If something is leaking a little on the compression tank it could let the air out but not leak water so it could be losing the charge after you drained it. try draining it again and see how much water comes out.
1 -
Also, are you bleeding air from the system anywhere? The air could be migrating out of the tank too.
0 -
Pictures below
Picture below - now at 12 psi matching the system supply.
Correct on both counts
I don't understand what you are asking.
I don't know what you mean.
No not yet. That is one thing I will try.
That's what used to happen before I solved my air problem. Air used to accumulate at the top of the system and I would have to bleed the radiator up there. This was due I think to installing the IAS backwards (doh). Once I corrected that no more air.
Valves - I have lots of valves - not a problem.
I have a 3 story house. How do you check a PRV? In previous years it would only get up to low 20s, but I think that was when air would get into the system because the IAS was not correctly installed. Another factor is that the setpoint was at 160, now it gets ratcheted up to 170 by the "boost" feature of the ODR which I just installed this season.
Not bleeding air anywhere anymore.
***PICTURES***
Piped from IAS up to compression tank
Continuing on to compression tank.
1" copper transitioning to Airtrol / tank.
Gauge mounted below tank,
System supply readings after cooldown.
0 -
Hmm. 12 psi cold should be fine.
Testing the pressure relief valve entails manually opening it for a bit. If it's defective it may leak afterwards, hence having another one ready to swap.
I'm thinking you may not have enough air in your tank despite what the Airtrol says.
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.0 -
airtrol doesn't say or set anything, that gage is only reading the system pressure that is being read everywhere else, and in this case, true PONPC,
what would be telling is that some tanks have fittings for a sightglass which would show air / water level in the tank, if the glass was there I would bet on "Topped Out"
like @Jamie said, isolate the tank, drain it, it's waterlogged,
isolate at the air sep, and at the makeup water feed,
known to beat dead horses0 -
I agree with that. The Airtrol is designed to establish the water level so the tank is half full (24" diameter tank, 12" airtrol). If I could trim say 4" off the Airtrol perhaps that would alleviate the problem.
Thanks for all the input. My own analysis is as follow:
- Adding radiation to the system (net gain) without increasing the size of the compression tank has led to insufficient air cushion to accommodate the increased water volume in the system.
- Before I fixed the problem of air getting into the system, that air provided some extra space for water to expand into. I lost that extra cushion when I installed the IAS correctly.
- Using a nightly setback means the system runs for a long time in the morning when heating the water of the entire system. Thus "boost mode" of the ODR incrementally raises the setpoint by 10F to the max value of 170 (before I had it set to I think 160).
I still need to check for a water-logged tank.
Solutions:
- Increase the air capacity through an auxiliary tank.
- lower the base system pressure.
- turn off the "boost mode".
- lower the amount of water in the compression tank (thus increasing air capacity).
Thoughts?
—Eric
0 -
number one is to check how much air is in the tank now.
10 f degrees isn't going to make a big difference in the pressure. unless you added a lot of volume that isn't your problem either.
if you have the valves to do it, drain the tank all the way with it valved off from the system then close the valves and let it fill with as little water as possible.
1 -
That indeed is my plan. Let me better explain the 10F : that is how much the setpoint is increased from the ODR value, with the increase occurring for every 30 minutes of continuous operation.
Right now ODR has the setpoint at 142F. So in the morning, to recover from the setpoint, the system ran for over 90 minutes, and the setpoint thus increased to 170 (max value).
That's a difference of 28F, almost 30F, which I do think makes a difference. Of course without the boost, the system would take even longer to heat the house with the setpoint at 142F.
I could eliminate the setpoint, but we like to sleep with cooler conditions.
—Eric
0 -
There's nothing wrong with your cold system pressure — the gauges seem to reasonably agree on 12 psig or so. If the pressure rises to more than 17 psig or so when the system is running, you simply don't have enough air in that compression tank. So… describe exactly how you are emptying it and reconnecting it, if you would.
Also, are there any other air removal devices anywhere on the system? With a compression tank, there shouldn't be. Which leads me to another question: did this problem show up just this season? Was it there before the newer boiler with outdoor reset was installed?
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England3 -
Here are the steps I followed:
- Shut off power to boiler.
- Close the valve from the boiler to the tank.
- Close the valve from the water supply to the tank.
- Open the valve below the tank and drain the tank.
- Open the Airtol fitting and also the valve to the water supply.
- Fast fill the tank until water starts to come out of the Airtrol.
- Close the valve to the water supply and close the Airtrol.
- Set the desired pressure in the tank using a Schraeder valve connected to the bottom of the tank.
- Open the valve to the boiler and the valve to the water supply.
- Restore power to boiler.
The only air removal device in the system is the IAS.
Yes the problem only started this season, after I added the ODR to the existing boiler (Burnham ES2).
Also refer to my earlier comments for my analysis of the problem.Thanks,
Eric0 -
I see your problems now. Just drain the tank, close the valves and bring the system back up to pressure. Don't add water to the tank beyond what goes in there when you connect it back to the system and use the prv/fast fill lever to bring the system back up to your cold fill pressure and don't add compressed air to the system. Adding compressed air is for bladder type tanks.
1 -
Oh dear. There's the problem. Once the tank is drained, close the drain and the Airtrol drain. You don't want to let any of the now trapped air out. See @mattmia2 's comment just above.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
You don't have enough air in your expansion tank
Chang your procedure for adding Air to the tank as follows.
Here are the steps I followed:
- Shut off power to boiler.
- Close the valve from the boiler to the tank.
- Close the valve from the water supply to the tank.
- Open the valve below the tank and drain the tank.
Open the Airtol fitting and also the valve to the water supply.Fast fill the tank until water starts to come out of the Airtrol.Close the valve to the water supply and close the Airtrol.Set the desired pressure in the tank using a Schraeder valve connected to the bottom of the tank.- Close the valve that drained the expansion tank
- Open the valve from the boiler to the expansion tank
and the valve to the water supply.- Allow the automatic water feed to get the system pressure up to 12 PSI (needed to fill those third floor radiators)
- Restore power to boiler.
If you have 100 gallons of water at 40° and you heat that water to 200° you end up with about 104 gallons of water. The air in the expansion tank is where that extra water goes. If there is only enough room for 4 gallons of water in that tank then the air will compress to 100 PSI or more. If there is 8 gallons of air space in that tank, then the opressure may only rise to 35 PSI. (still to high for that relief valve). But if you have 15 gallons of air in that tank then the 4 extra gallons of water will compress that 15 gallons of air to maybe 18 PSI (because there is more air to compress) so if there is 18 or 19 gallons of air space in that tank, the pressure will only rise from 12 to maybe 16 PSI.
The more air in the tank the lower the pressure will be when the water gets hot. The only thing you need to do is add air to the expansion tank.
By the way @pecmsg was referring the the pre-charged expansion tanks. You don't have one of them, so you would be confused by his statement. It does not apply to your system.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
2 -
If that dielectric coupling and black pipe and nipples have been there awhile, they could very well be clogged. Dielectric couplings are not needed and are famous for debris buildup. If that pipe is occluded, it will very well prevent the x-tank from being part of the system.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab0 -
This is what I'd do.
All Steamed Up, Inc.
Towson, MD, USA
Steam, Vapor & Hot-Water Heating Specialists
Oil & Gas Burner Service
Consulting1 -
All good advice - I'll try it out when we get a warm spell.
The tank is 24 gallons which I think I forgot to mention.
i don't see that there's a difference how the air gets compressed - whether with an air compressor, a bicycle pump, or (more slowly) through the water fill valve.
The thing is, when using the water fill valve, I will have no idea how much water is in the tank. Maybe there is a formula for calculating that based on initial state of an empty tank at 0 PSI, and a tank pressurized at 12PSI?
The advantage of the Airtrol is that when water comes out, I know there are are 12 gallons of water in the tank,—Eric
0 -
That was installed last fall so I don't think that's the problem right now.
1 -
Actually, there is a formula for how much air is in the tank. The basic gas formula: pressure times volume is a constant. The ringer in that formula is the pressure is absolute pressure (psia) (referenced to a perfect vacuum), not gauge pressure (psig). Most people think in terms of gauge pressure quite naturally — but that is the pressure relative to atmospherc pressure, and is of no use in the gas formula.
So. In this situation, your initial absolute pressure in the tank — empty,open to the air — is not zero, but is about 15 psia (depending on your elevation above sea level and weather — but that's close enough). You have a 24 gallon tank, so that is your volume. Now let's suppose that you raise your system pressure to 12 psi gauge (why I almost use the correct abbreviation — psig). What is your volume of air going to be? Well, initially you 24 gallons of air times 15 psia, and now your absolute pressure is 27 psia so the final volume of air is 13 gallons. Then we increase the volume of the water in the system by 4 gallons due to temperature change. That means the volume of air has to be 9 gallons instead of 13. What will the pressure be? Well, we had 13 gallons at 27 psia, so now we have 9 gallons of air at 24 psig. No problem. In fact, not surprisingly since that is the way the compression tank and Airtrol system was designed, that's just about the same as your half a tank of water accomplished with your air compressor — but with a good deal less effort.
Where you get in trouble with a compression tank is when, for some reason, the air is removed from it. The most common way for this to happen is for there to be an air removal fitting somewhere on the system, and having such a thing is common because with a modern bladder tank you don't want any air anywhere in the system. What happens is the air gradually migrates out of the compression tank, so your initial volume of air is less — and the pressure has to rise more with the decrease in air volume. If you lost half the volume of air the pressure hot would be about 65 psig. OOOOPS.
I hope this helps…
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England2 -
This. Don't worry about the Airtrol fitting. Start with an empty tank, fill system with water to 12psig, done.
I think Jamie is on to something. You're losing your air charge somewhere. Any other air elimination devices besides the scoop?
Trying to squeeze the best out of a Weil-McLain JB-5 running a 1912 1 pipe system.0 -
There are no other air elimination devices in the system. I am 100% positive of that.
When I get a chance, and the system is at room temp, I will drain the tank and measure how many gallons were in there. That should indicate if the tank was somehow waterlogged. It should be around 12 gallons (half the tank capacity).Here's something that happened last year. After re-piping the near boiler piping to install a Caleffi thermostatic valve, there were 2 or 3 places with slow leaks. I neglected to turn on the water supply to the boiler, and over time I observed that the system pressure at rest was slowly dropping. Because water was (very slowly) leaving the system through these slow leaks. Those leaks were fixed (well there is still one very slow leak) and this year I turned the water supply and the regulator has apparently been doing its job.
My boiler is in the basement of a 3-story house so I was pretty sure I would not encounter a low water problem.—Eric
0 -
There doesn't need to be any water in the tank when the system is cold and presurized. The city water pressure is just used to pressurize the tank for convenience. Technically you could fill the piping just to the tank with water and pump air in to the tank to pressurize the system. If the tank was already half full at atmospheric pressure, when you added water to the tank to bring the system to the cold fil pressure you probably filled it to roughly 3/4 full of water.
Very small leaks from things like shaft seals and gaskets and valve packings are normal. The tiny amount of water you need to add for those leaks won't make the system corrode if it is weeks or months between additions.
1 -
If the house is three stories and all three are heated, the cold fill pressure should be closer to 17 psig than 12.
—
Bburd0 -
It would be better if you knew that there is 8 gallons of water in the tank when it is cold and 12 gallons when the entire system is hot. Can you do that?
I believe that you are telling us that you fill the tank with water to the top of the Airtrol tank fitting tube. If that happens at 0.0 PSI Gauge pressure than you are starting out with 12 gallons of air in the tank ar 0.0 PSI gauge pressure.
I would suggest that you start with 24 gallons of air in the tank ant 0.0 PSI Gauge. then when you add the water pressure from the system to that tank, the air pressure will increase to the pressure of the system. That happens when the 12 PSI water compresses the air in the tank by filling the tank with 12 PSI water. At that point the tank will have more air in it than if you let the water fill the tank to to top of the Airtrol fitting tube at 0.0 PSI Gauge pressure.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
3 -
Yes I m saying that there are 12 gallons of water in the tank when I fill the tank to the top of the Airtrol fitting. So there is also 12 gallons of air and the pressure gauge reads 0.
You seem to be suggesting two things though, starting with a gauge pressure of 0:
- start with 8 gallons of water
- start with 0 gallons of water
Either way, if I then pressurize the tank with water to 12 PSI, I don't know how much water that will add (and correspondingly how much air is left in the tank). That is why I took the step of pressurizing the tank by adding air rather than water, so that I was starting from a known state. I don't see that it makes any difference how the tank is pressurized.
—Eric
0 -
It's good to have the site glass on those tanks to see exactly where the air is. Does your tank have the two connections for a glass?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Pretty sure we're all suggesting start with 0 gallons of water in the tank at 0 psig.
why do you want more water in the compression tank?
2 -
except that is like 8 more places where it can leak the air charge out.
1 -
Back to square one. How it happens makes no difference at all — but when the system is cold you want to have about half a tank (12 gallons) of water in the tank and half a tank of air at 12 psig or 27 psia in the top of the tank.
You can do this by starting with an empty tank (0 psig) with all the drains or vents closed and adding water through the system connection to the Airtrol (half full — the air will now be at about 12 psig/27 psia). That's the easy way the old timers used. You can add it, if there is a Schrader valve, by filling the tank half way with water and then using a compressor, bicycle pump, or whatever to bring the air pressure above the water up to that 12 psig — so long as the volume of water isn't allowed to change while you are doing it.
How you get there is completely irrelevant.
I'm not sure where the idea of starting with 8 gallons of water at 0 psig came from… that's just wrong.
And I explained above how to determine how much water and air there is in the tank at any air pressure, provided only that you know the volumes and pressure at some stated point.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0
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