Axiom mini feeder question

hot_rod

Taking a shower should have no effect on the pressure in the coil/ hydronic side of the system. The Axiom gauge should not move.

The pressure in hydronic system, assuming no leaks will go up and down as temperature increases and decreases. It has to, as water is heated it expands. This expansion pushes against the diaphragm in the tank an as it does this gauge will rise.

Here are tables to show that concept. If you want to know that much?

Also a link to a You Tube on expansion from a former Amtrol trainer. At minute 1:08 he explains why pressure must go up as water is heated in a closed loop system with a properly sized and pressurized system.

https://www.youtube.com/watch?v=F8rlAUmb-pM&list=PLuuV0ELkYb5VE0I4evUZ30b5U78CRlRdg&index=102&t=1704s

Your tank needs to be removed from the system. An air gauge to check and adjust to the pressure the on that air stem at the end of the tank. Set it to 12psi.
then set the Axiom to 12psi.Axiom will fill to, make it 12 psi.

To use these charts:

We can allow hydronics to rise to 27 psi typically, 3 below below the relief valve setting.

So with the acceptance chart go from 12 psi fill to 27 max.pressure and the factor is .36, 36%.
So at 27 psi the tank will have 36% water in it, 64% air.

When the system is at 12 psi,and the tank was charged to 12psi, there is no water in the tank!

Next table shows acceptance volume, what size the tank needs to be based on how much fluid is in it.

Assume your system holds 30 gallon. Temperature goes from 50- 140F.
.0149 is the expansion factor.
In a 30 gallon system is is 30X .0149= .447. the smallest tank you can buy is a #15, plenty for a small volume low temperature swing system.

If you can valve off the Axiom from the system and pressure continues to rise and pop the relief, it could be the Axiom pressure valve is bleeding by. It keeps allowing a trickle of water into the system.

Or I would suspect a pinhole in the coil. So tank water pressure, maybe 60 psi? is crossing into the hydronic side.

moemah123

Thanks hotrod. I will ask him to check the expansion tank pressure. 

I just need to be clear on what you said. You said taking a shower has no effect on axiom. But said temp change I.e. tank heating up is normal to cause axiom to fluctuate? Did I understand right. If yes, this means shower does have effect (because when I take shower it starts the system heating) so to be clear when system is heating up. That means I should expect pressure of axiom to increase? And that this limit should be 27 psi? And when tank stops heating pressure should drop back to 12psi and stay there?

hot_rod

Correct, if the heater fires up obviously temperature increases, so does the temperature in that coil inside that is the hydronic loop

The coil inside that tank holds about 3 gallons of water, so it will see some temperature and pressure increase.

unless your system has a lot if volume in the piping, that tank you have when charged properly will show a small amount of pressure increase

If you knew the hydronic system volume, you could calculate all this with those tables.

start with the easy steps, remove and properly charge the tank

Fill the system to the same pressure as the tank.  Unplug the Axiom so it cannot add pressure, monitor the gauge for a few days

GroundUp

What does the other gauge in the actual piping to the right of the pump say? Does it move? Perhaps the Axiom is just fighting itself if everything is valved off. Assuming the water heater is working properly, it should only vary the average tank temp 10-15 degrees which should have no effect on the heating side's pressure in a perfect world. With everything valved off, your actual heating side volume is probably less than 5 gallons, which would explain the drastic pressure swings with minimal temp swings (since 70% of that volume is inside the water heater)- if the expansion tank is not properly charged. A proper hydronic system with a properly sized and charged expansion tank should always remain at nearly the same pressure, regardless of fluid temp. I've got a Frankenstein system at home that I built for demonstration purposes which can be wildly varied in temps and volumes. Whether a 9 gallon or 240 gallon total volume, the system pressure is 11 psi at 40 degrees and 12 psi at 170 degrees. The entire purpose of the expansion tank is to do exactly that- maintain a given system pressure with expansion and contraction. Something as small as yours with minimal temperature rise, no more than 1 psi variance is acceptable.

Your expansion tank should be removed and pressurized via the Schrader valve on the bottom to probably 12 psi, then reinstalled. Then the relief valve should be replaced with a new one and reoriented to a vertical position. Then the water side should be brought up to 12 psi, probably via the Axiom now that it's unnecessarily there. At this point, there should be no more surprises and your system should work as well as it can for what it is.

hot_rod

Actually the purpose of an expansion tank is to accept the expanded volume of the water as it is heated. it is not to guarantee the system pressure doesn't rise.

On chilled water systems you would want to over-charge the tank, so system pressure, indicated on the gauge, does not fall as the molecules get smaller. This static pressure decline this could cavitate circulators. Same thing happens in solar thermal that could see a 300°∆ T.

If the tank is an open vessel you would not see a pressure increase. Or a closed system that has a leak somewhere

As a demo, fill a sauce pan to the top with water. Put it on a burner and turn up the heat. (keep a dish towel nearby Did the water level rise? Over the top of the pan? That is an indication that water expands as heated. It the lid was tightly sealed with a pressure gauge, pressure would increase above atmospheric.
See this demonstrated if you have a pressure cooker.

More specifically the billions of molecules within the fluid take up more space as they are heated, the amount of fluid doesn't actually stretch or increase.

The expansion tank could be considered a spring. As heated water pushes into the tank, pressure on the air side also increases, just as the spring would on the side opposite of the force.

As the water is heated and pushes into the tank, check the air pressure on the tank, it too is rising in relation to the thermal expansion. It has too in a closed system. Figure 12-2

Water heated from 40- 170F use an expansion factor of .02418 regardless of the volume in the system.

240 gallons of fluid X.02418 = 5.8 gallons of acceptance required.

Modern Hydronic Heating, fourth edition has 15 pages on expansion tanks. Theory, design, sizing, graphics, etc. if you want a deep look into expansion.

Tables and explanations in the Amtrol handbook also.

Alan (California Radiant) Forbes

With those valves closed, you are separating the water heater from the Axiom and the distribution piping including the manifold(s). The only thing that will increase the pressure is the Axiom and the only thing that will decrease the pressure is a leak somewhere.

Have you told us what pressure the Axiom is set to? Factory setting is 18 psi.

What part of the country are you in? City, state?

This is a very unusual situation and you have a lot of people scratching their heads.

GroundUp

I guess it's difficult for some to digest the notion of "properly sized and charged".

hot_rod

GroundUp said:

I guess it's difficult for some to digest the notion of "properly sized and charged".

Happy to see you agree with the math, science, and sizing tables

moemah123

Alan (California Radiant) Forbes said:

With those valves closed, you are separating the water heater from the Axiom and the distribution piping including the manifold(s). The only thing that will increase the pressure is the Axiom and the only thing that will decrease the pressure is a leak somewhere. Have you told us what pressure the Axiom is set to? Factory setting is 18 psi. What part of the country are you in? City, state? This is a very unusual situation and you have a lot of people scratching their heads.

I am pretty sure and have it on video that even with valves closed the axiom reading of pressure increased when heater is on and drops when heater goes off. Which is why I am also scratching my head. It makes no sense. I live in seattle, Washington 

Axiom is set to 17 now. Example scenario.. heater kicks up Axiom goes up continuously even exceededing 26 psi warning sometimes to 29 psi or till tank shuts off heating. Then it drops again slowly to whatever psi sometimes as low as 16 in 2 hours then heater back on and cycle repeats. I cannot understand it with loops closed how is it possible

I was asked above what psi guage near pump says actually it has been going down. When i created thread it was 20 psi. Now its 10psi

moemah123

GroundUp said:

What does the other gauge in the actual piping to the right of the pump say? Does it move? Perhaps the Axiom is just fighting itself if everything is valved off. Assuming the water heater is working properly, it should only vary the average tank temp 10-15 degrees which should have no effect on the heating side's pressure in a perfect world. With everything valved off, your actual heating side volume is probably less than 5 gallons, which would explain the drastic pressure swings with minimal temp swings (since 70% of that volume is inside the water heater)- if the expansion tank is not properly charged. A proper hydronic system with a properly sized and charged expansion tank should always remain at nearly the same pressure, regardless of fluid temp. I've got a Frankenstein system at home that I built for demonstration purposes which can be wildly varied in temps and volumes. Whether a 9 gallon or 240 gallon total volume, the system pressure is 11 psi at 40 degrees and 12 psi at 170 degrees. The entire purpose of the expansion tank is to do exactly that- maintain a given system pressure with expansion and contraction. Something as small as yours with minimal temperature rise, no more than 1 psi variance is acceptable.

Your expansion tank should be removed and pressurized via the Schrader valve on the bottom to probably 12 psi, then reinstalled. Then the relief valve should be replaced with a new one and reoriented to a vertical position. Then the water side should be brought up to 12 psi, probably via the Axiom now that it's unnecessarily there. At this point, there should be no more surprises and your system should work as well as it can for what it is.

The PSI guage on heating pump is actually going lower on time of thread creation it was 20psi, now around 10-12 psi and going lower day by day (I dont see spiked movements) Axiom reading pressure is one thats going higher when heating and lower when system is quiet. I would have understood fighting itself if it was doing it randomly i.e. going up randomly, but it never goes up unless heater kicks in. I am scratching my head

GroundUp

Maybe stop worrying about things that don't matter, and have the guy fix what we've told you is wrong with the system. Unplug the Axiom and forget about it until he's back. Or spend 15 minutes and fix it yourself. I'm sorry, but you're really making a mountain out of a mole hill here.

moemah123

hot_rod said:

Actually the purpose of an expansion tank is to accept the expanded volume of the water as it is heated. it is not to guarantee the system pressure doesn't rise. On chilled water systems you would want to over-charge the tank, so system pressure, indicated on the gauge, does not fall as the molecules get smaller. This static pressure decline this could cavitate circulators. Same thing happens in solar thermal that could see a 300°∆ T. If the tank is an open vessel you would not see a pressure increase. Or a closed system that has a leak somewhere As a demo, fill a sauce pan to the top with water. Put it on a burner and turn up the heat. (keep a dish towel nearby Did the water level rise? Over the top of the pan? That is an indication that water expands as heated. It the lid was tightly sealed with a pressure gauge, pressure would increase above atmospheric. See this demonstrated if you have a pressure cooker. More specifically the billions of molecules within the fluid take up more space as they are heated, the amount of fluid doesn't actually stretch or increase. The expansion tank could be considered a spring. As heated water pushes into the tank, pressure on the air side also increases, just as the spring would on the side opposite of the force. As the water is heated and pushes into the tank, check the air pressure on the tank, it too is rising in relation to the thermal expansion. It has too in a closed system. Figure 12-2 Water heated from 40- 170F use an expansion factor of .02418 regardless of the volume in the system. 240 gallons of fluid X.02418 = 5.8 gallons of acceptance required. Modern Hydronic Heating, fourth edition has 15 pages on expansion tanks. Theory, design, sizing, graphics, etc. if you want a deep look into expansion. Tables and explanations in the Amtrol handbook also.

Hotrod apologies but I am confused now on suggestion of making expansion tank 12 psi if it doesn't contribute to pressure. As a non technical person what should I tell my heater guy to convince him to lower expansion tank psi, how will that make my system behave better. Since this and changing valve orientation are my key takeaways. 

hot_rod

The expansion tank is just an empty tank with a rubber disc across the middle of the tank. Before you install it you check the pressure with a tire gauge. Typically the tanks leave the factory with 12 psi in them. So you set the fill pressure either with a fill valve or the Axiom to 12 psi. As the water heats up and expands it pushes into the expansion tank against that rubber disc.

If the gauge on the boiler or Axiom reads 20 psi when it heats up, the air stem on the tank will also read 20. It just accepts the water as its volume expands when heated.

The graphics I attached above show a visual example. It sounds like something is funky in the Axiom, whatever regulates it output pressure seems to be the problem.

Ideally the system would be leak free and not need an Axiom or fill valve. That should be the installers first quest, make your system leak free.

moemah123

GroundUp said:

Maybe stop worrying about things that don't matter, and have the guy fix what we've told you is wrong with the system. Unplug the Axiom and forget about it until he's back. Or spend 15 minutes and fix it yourself. I'm sorry, but you're really making a mountain out of a mole hill here.

You are perfectly right. I will stop worrying at current state of system until he is back.

One more question. Is axiom really wrong answer here and autofill is the answer? Having 2 heater guys mentioned it I was forced into this situation. To recover and prepare for future. My whole system is due to be replaced in 5 years if we respect boiler life of 12 years.  How can I educate myself to what new system and essential components it should have and what is the expected state as it heats a 1600sqft house. I feel this whole thing should be easier and installers should be knowledgeable but no one seems to have half knowledge you guys have and I pay them alot for nothing (at this point using space heaters is way cheaper for what I am being asked) 

hot_rod

Nothing wrong with an Axiom solution for a fill system

My concern is if there us a leak in the system, you should not be adding fresh water constantly, regardless of having a fill valve it Axiom.  If you can tightly valve off the Axiom does boiler pressure continue to drop? Does it go to zero. If yes, how quickly it drops indicates how big of a leak you have.

As for a re pipe of the boiler room, plenty of good option in the Caleffi Idronics series, a free downloadable tech journal series.

GroundUp

Sorry, I didn't mean to imply that the Axiom is wrong. For a glycol system, it's a great solution for makeup water. The pink in your lines imply that there was glycol in the system which would make sense that they added the Axiom, but then he added water instead of glycol which doesn't make any sense. With a regular water makeup, a simple autofill would have been 1/8 the price of the Axiom and perform the same duty with no electricity or other junk necessary. There is nothing wrong with having it, it's just a very large unnecessary expense is all.

A proper leak-free hydronic system will never need makeup water. I install 2-3 systems per week and can count on 1 hand the amount of times I've added a feeder of any sort. Leaks happen, but at that point it's best to find and repair the leak versus just adding more fluid to replace it with and hiding the actual problem. You mentioned the gauge near the circ is dropping but very slowly, which probably does indicate a leak. That's the one that should be referenced, not the Axiom one. The fact that you expansion tank is overcharged means there is no water in the actual tank, so the system volume is quite low. Even a few drops per day can cause the pressure drop that you're seeing. A few drops per day should have some visible sign though, and not all that difficult to locate unless it's buried in a wall or something.

moemah123

hot_rod said:

Nothing wrong with an Axiom solution for a fill system

My concern is if there us a leak in the system, you should not be adding fresh water constantly, regardless of having a fill valve it Axiom.  If you can tightly valve off the Axiom does boiler pressure continue to drop? Does it go to zero. If yes, how quickly it drops indicates how big of a leak you have.

As for a re pipe of the boiler room, plenty of good option in the Caleffi Idronics series, a free downloadable tech journal series.

Answering your and groundup question

Before Axiom was installed I had a post that it took 1 month for pressure to drop to 0 from 40psi. When I contacted my new heater person he suggested Axiom and testing system for leaks. He installed Axiom then finally agreed manifold was leaking so will replace that.

Now, I waited a few days to see how it drops. It is still dropping slowly but is nearing 0. Both heater guys attributed this pressure drop to manifold leak that we could touch and feel is leaking, but he shut off system loops until he replaces it. This is again my own ignorance, if manifolds for hydronic system is closed and the system is not passing water through pipes, what is the pressure guage showing? Is it not normal to drop since system is not in use ? Or the guage showing lost pressure because of that leaky manifold? I understood before Axiom pressure dropping due to heater being used in winter and leak possibility. But it is summer and loops shut off so I don't know how pressure is going down

Other than that nothing in boiler room or other manifolds room / walls where they are installed show any leak what so ever (other than rusty manifold being slightly wet when system runs) The place they are installed is just dusty no sign of any water damage. So if leak is happening and water is not circulating, I don't know how this could be

GroundUp

It doesn't matter if the system is circulating or not. Think of the system as a pressurized vessel- if there's a leak, there's a leak. Period. Are there isolation valves on the system side of the leaking manifold? Do they hold 100%? If you're referring to the crappy 1/4 turn valves on the loops themselves, they probably aren't holding and that's why you're seeing a drop in pressure.

moemah123

GroundUp said:

It doesn't matter if the system is circulating or not. Think of the system as a pressurized vessel- if there's a leak, there's a leak. Period. Are there isolation valves on the system side of the leaking manifold? Do they hold 100%? If you're referring to the crappy 1/4 turn valves on the loops themselves, they probably aren't holding and that's why you're seeing a drop in pressure.

Where can i locate what you are asking? I am not sure also which 1/4 valve you are referring to. I shared pics of my system if you can point me to them in the pics. Also, what more pics should i share to see what you suspect?

GroundUp

I had to look back at your post from last year to see your manifolds and now see that the crappy 1/4 turn valves I referenced are not present in your system, so disregard that. The valve to the immediate right of the pump and the one below it, the way it looks, are isolating the manifolds from the system. Guessing that pex off to the right simply travels up through the subfloor and terminates at the manifolds? If that is the case, and those two valves are holding tight, the pressure drop you're seeing on the manual gauge by the pump is a leak on the manifold side of those valves. The drippy manifold in question is likely the culprit there.

Now on the other side of the system, you're relying on the Axiom to tell you what's going on. If there is no visible leakage, there are no leaks. Forget what the Axiom says and just unplug it until the manifolds are replaced, relief valve is fixed, and expansion tank is properly charged. Only at that point is there potential cause for concern.

moemah123

GroundUp said:

I had to look back at your post from last year to see your manifolds and now see that the crappy 1/4 turn valves I referenced are not present in your system, so disregard that. The valve to the immediate right of the pump and the one below it, the way it looks, are isolating the manifolds from the system. Guessing that pex off to the right simply travels up through the subfloor and terminates at the manifolds? If that is the case, and those two valves are holding tight, the pressure drop you're seeing on the manual gauge by the pump is a leak on the manifold side of those valves. The drippy manifold in question is likely the culprit there. Now on the other side of the system, you're relying on the Axiom to tell you what's going on. If there is no visible leakage, there are no leaks. Forget what the Axiom says and just unplug it until the manifolds are replaced, relief valve is fixed, and expansion tank is properly charged. Only at that point is there potential cause for concern.

One last question as heater guy is coming this week. What about the expansion tank on my boiler what PSI should that match if expansion tank will be set to 12ish psi in hydronic side?

GroundUp

We've been over this several times already, but again, those numbers should match. The air pressure needs to be adjusted while there is no pressure on the hydronic side. Sometimes removing the tank to adjust air pressure eliminates any influence. Set that air pressure to 12, then reinstall the tank and fill the hydronic side to 12.

moemah123

GroundUp said:

We've been over this several times already, but again, those numbers should match. The air pressure needs to be adjusted while there is no pressure on the hydronic side. Sometimes removing the tank to adjust air pressure eliminates any influence. Set that air pressure to 12, then reinstall the tank and fill the hydronic side to 12.

Apologies, I assumed we always talked about only hydronic expansion tank not one connected to my combi cor boiler for domestic water 

So both domestic water expansion tank and hydronic system expansion tank is 12 psi even if water pressure is 30 psi correct?

GroundUp

No. Leave the domestic alone.