Expansion tank not taking the extra pressure.

MikeAmann

I added an 40 gallon indirect water heater to my boiler. I went above and beyond and plumbed it according to Massachusetts code, meaning that I added a check valve and vacuum break in addition to the expansion tank on the CW inlet side. I followed the directions for charging the tank. The boiler's tankless coil is still in operation and is plumbed AFTER the new IWH. I have a pressure gauge on the line going into that coil. I have the incoming cold water line pressure regulated to 50 psi after the water meter. When the tankless coil is hot, there is no change in pressure. But when the IWH is hot, the pressure increases to nearly 70 psi. Why is my expansion tank not taking the increase in pressure? Do I just need to lower the air pressure?




Here is the flow path: 50 psi CW to shut-off valve > spring check valve > vacuum break and expansion tank > inlet IWH tank > outlet IWH tank > hot water filter > inlet tankless coil > outlet tankless coil > to fixtures.

Zman

Did you precharge the tank to house pressure prior to installing it?

EBEBRATT-Ed

Yeah I don't remember what pressure the domestic those tanks come pre charged at (55psi) but the air side has to match you incoming water pressure. In addition I would have left the ck valve out but that does not matter if it's off a prv line

hot_rod

Hard to tell from the pic, is that a # 15 or 30 tank?

MikeAmann

Yes I pre charged the tank to 50 and I think it was factory preset to 45 psi. It's almost as if the diaphragm is stuck to the tank itself and just needs a little "kick" to get it working. I have valves installed everywhere, so I will try to close a valve in the line after the tank and increase the incoming pressure to get the diaphragm unseated.

MikeAmann

It is an Amtrol Therm-X-Trol ST-5 (2 gallon) and is the size specified by the IWH manufacturer. I am set to 140 degrees (use first chart).

hot_rod

Ther have been reports of diaphragms stuck up against the nipple, on new tanks, rendering the tank unable to take any expansion 

MikeAmann

I will be addressing the issue in about 1 hour. I hope that's all it is. It seems like it.

EBEBRATT-Ed

@hot_rod

Just curious, do you know what typical pressure rise they select those tanks at? You going to get some pressure rise when the water heats especially with a check valve in the cold water

EBEBRATT-Ed

a 40 gallon indirect filled with 40 deg water and heated to 140 a 100 deg rise will increase in volume 2.5% so 40 x 1.025=41 gallons

mattmia2

Does the expansion tank sound and feel empty or full?

MikeAmann

I was wrong about the brand, the expansion tank is an Everbilt EF-TET-2T (2 gal) and is factory preset to 40 psi. I have it very solidly mounted, so I can't tell whether it's full of air or water by tapping on it.

hot_rod said, There have been reports of diaphragms stuck up against the nipple on new tanks, rendering the tank unable to take any expansion.
I thought this was the problem also. I closed the valve at the outlet of the IWH and then raised the incoming pressure from 50 to 100 psi. I have 110 coming into the house >>> the reason for the regulator. The extra 50 psi did not do the trick. Then I relieved that pressure and brought the incoming back to 50 psi. I had the boiler heating the water in the IWH during this and the pressure was now up to 60 psi. So I went ahead and completely let the air pressure out of the expansion tank. That did the trick, the diaphragm came off of the nipple. Then I relieved the pressure on the water side, charged the tank to 50 psi with air, and that is where the pressure seems to be staying. I will double-check it tonight.

EBEBRATT-Ed

Everbilt? Is that a HD tank? Hope it works

MikeAmann

I think I did get it at Home Depot, but it looks like a quality piece. I wouldn't have taken it out of the store if it was cr@p. We'll see.

MikeAmann

Last night, I ran the boiler again and let it heat the IWH. The pressure gauge went up to almost 80 psi. ****? I checked the air side of the bladder and it read nearly 80 psi. So I just kept letting air out until the gauge read 50 (water side) and so did the air side. I will see what happens from here..........

mattmia2

When you charged it, you had the water side open to atmospheric pressure, right?

MikeAmann

Yes, I did. And when I recharged it, I drained the IWH tank down enough so that was no pressure on the water side. Then I charged it to 50 psi (air) and then refilled the pipes. Because the tank is so close to the ceiling, I used a SharkBite fitting if I ever had to remove it. Maybe I will be doing that.
Something about this is not making sense. All I can think of is that the diaphragm has a hole in it, so I have a tank with some amount of water at the bottom with an air pocket sitting above it. However, both times when I let the air out of the valve, there was no water or even the slightest sign of moisture. What am I missing here?

MikeAmann

I removed the expansion tank last night. It only took 5 minutes to do because I used a SharkBite fitting on the tank. The diaphragm is fine with no leaks, nor is it stuck up against the nipple, I filled it with water and it took about 3/4 gallon, and the diaphragm moved from the weight of the water. The valve stem was removed while doing this. So I charged the tank to 50 psi on the bench and all I can think of as to why it wasn't working is that maybe I had a lot of air on the water side because the piping was new. The tank is mounted "upside-down" or air side up. The manufacturer says it can be mounted in any orientation.

So this time when I reinstalled the tank, I filled the pipes with water right up to the top where the SharkBite fitting slides on. I turned the water back on and the pressure in the pipe is 50 psi. We will see what happens once I get the new boiler and burner controls installed and the water is heated.

MikeAmann

Update: no difference.
I got my new controls installed and the pressure in the DHW pipe was 50 psi COLD (60 degrees).
With the IWH heated up to 140 degrees, the gauge reads 80 psi. Same as all the times before.
This never happened before I installed the spring-loaded check valve and expansion tank.
I do have a PRV right after the water meter, but the extra pressure was always able to push back against the incoming water supply.
There is a 3 gpm flow restrictor installed in the pipe going into the tankless coil of the boiler to limit the flow rate. But that has always been there. It is just an orifice (small hole). This has never caused a problem.
Maybe I should just remove the check valve and be done with this issue?

EBEBRATT-Ed

Doesn't make sense. The only thing I can think of is the tank not being large enough.

If the air pressure is 50 and the cold water is 50psi and you heat the water say 100 degree rise you will get about 1 gallon of expanded water the tank needs to hold.

It's a 2 gallon tank total capacity which seems like it should be large enough.

The only crazy idea of mine to test this is install a ball valve, a tee (boiler drain on branch) between the system and the tank. Start it up from cold and let it expand until the pressure gets up to 80 or whatever it wants. Close the ball valve, open the drain and measure how much expanded water you get.

Or put in a larger tank or take out the check valve

I am sure your sick of fooling with it but it would be nice to get an answer

MikeAmann

Good suggestion Ed, and now that I think about it, I already have valves in place that I can isolate that pipe and easily drain the excess at that red hot water filter (see pics above). It's right between the output of the IWH and input to the tankless coil. And being up high, I wouldn't be draining the pipes or tank - I would just capture the water from the excess pressure.
I did that because the IWH came with a sacrificial anode, and I didn't want any chance of any metals flowing into the tankless coil of the boiler. That is no longer an issue because I replaced it with a powered titanium anode (nothing dissolves). I installed another on the tank of the boiler to protect it too.

Yes, I don't like unanswered questions. My mind is the type that will become obsessed until I find the answer and solve the problem.

Jamie Hall

I'm not sure that 2 gallon total capacity really is enough space. If you had it half full, and at 50 psi, and had a half gallon of expansion to take up, the pressure would have to go up to almost 100...

MikeAmann

According to the IWH manual, a 2 gallon expansion tank is more than enough for a 40 gallon.
Ed even did the calculations.
a 40 gallon indirect filled with 40 deg water and heated to 140 a 100 deg rise will increase in volume 2.5% so 40 x 1.025=41 gallons

EBEBRATT-Ed

@MikeAmann

What they don't tell you is what the pressure rise would be when the water is heated. Amtrol has all the calculations in their manual. I will try and figure it out.

You know what? I think @Jamie Hall are going to the same destinations but maybe on differente roads.

If you read the note above under the Amtrol Chart it says" 40 deg entering water with a 150 PSI RELIEF VALVE.

So we are used to boiler systems when a 12-15 psi expansion tank gets to 23 psi we start to sweat.

I think you will find nothing is wrong with the tank it's all in the way they calculate the size.

MikeAmann

I double-checked tonight and I do indeed have all the valves I need to do Ed's test. I have to let the tank get cold first.

EBEBRATT-Ed said:

@MikeAmann

What they don't tell you is what the pressure rise would be when the water is heated. Amtrol has all the calculations in their manual. I will try and figure it out.

You know what? I think @Jamie Hall are going to the same destinations but maybe on different roads.

If you read the note above under the Amtrol Chart it says" 40 deg entering water with a 150 PSI RELIEF VALVE.

So we are used to boiler systems when a 12-15 psi expansion tank gets to 23 psi we start to sweat.

I think you will find nothing is wrong with the tank it's all in the way they calculate the size.

Thinking about this, my entire boiler tank and all the piping for the house baseboards probably is 30 gallons MAX. The boiler side uses a 4.5 gallon expansion tank. I can tell you exactly how full this tank is when the water is 200 degrees - 1/4 full. And the pressure gauge might increase by only 5 psi from completely cold to 200 degrees.


The IWH is 40 gallons and uses a 2 gallon expansion tank. Maybe it is too small?
If that is what I find, then I will just remove the check valve. I do have a vacuum break installed, so if the supply pressure ever dropped, creating a vacuum, the water would not get sucked out of my system.

hot_rod

You could buy another one that size and connect both, instead of starting over with one larger size

MikeAmann

I do believe that the expansion tank is working in that it gives the "expanded" water a place to go. But it does nothing about the pressure increase issue, I will do Ed's test tonight to measure how much the water expanded due to the temperature increase (volume). I tried last week, but the IWH was not fully cold, so the test was not completely valid. But I did hear the water flow out of the expansion tank once the pressure got down to the 50 psi set point. To capture just the water due to expansion only, I will have to shut the valve just before the gauge reaches 50 (from 80 to 51).

As long as the tank is actually working, then I will just remove the SharkBite check valve and let the pressure increase push back against the street supply, as it did before. I just don't want the added pressure in the tankless coil if it can be avoided.

Jamie Hall

You are aware that as the expansion tank absorbs the extra that the pressure must rise?

The sizing of the expansion tank is to ensure that the pressure rise is acceptable. If you want less pressure rise, you need a bigger expansion tank...

EBEBRATT-Ed

I don't claim to knwo how to calculate the pressure rise.

Common sense tells me that with 50 psi of air on air side and 50 psi of water on the water side the bladder should be in the middle.

If it's a 2 gallon tank then you would have 1 gallon of water in the water side at 50 psi.

Which occupies 233 cu inches. Now we know that expanding 40 gallons of water in the indirect will produce about 1 gallon of expanded water which requires 233 cubic " area

Some of this expanded water goes into the tank increasing the pressure above 50 psi

How to calculate the "how much" and what the ending pressure will be is above my pay grade

WMno57

EBEBRATT-Ed said:

How to calculate the "how much" and what the ending pressure will be is above my pay grade

for extra credit ..............

How much will temperature rise within the air space? Assume no loss to tank walls, and no heat transfer from the water.

Jamie Hall

Oh come on, @EBEBRATT-Ed . I'll bet you could do it in your sleep...

Fortunately, however, if the tank was initially pressurized to 50 psi, and the water pressure starts at 50 psi, the tank won't be half full of water -- it will be almost entirely air in there. So to start, we have 2 gallons of air at 50 psi. Now the ringer in the deck is that we need to consider absolute pressure -- not gauge pressure. So the absolute pressure is 65 psia.

Now there is a useful little equation here... if the temperature doesn't change, the product of pressure and volume is a constant for a given arrangement. So. Ignoring units (oh dear...) we have 2 gallons at 65 psia, and the product is then 130 gallon-pounds per square inch (what a horrible set of units that is!). Now if we want to find the pressure needed to squeeze the thing down to 1 gallon instead, just divide that constant by the new volume -- and we get 130 psia, or 115 psi.

Which would be more pressure than I'd want, so I'd seriously want to start with a larger tank!

Now temperature. That much compression won't raise the temperature much. It would, if it were fast enough and no heat were lost (and one can calculate it, since a more complete equation is that pressure times volume divided by temperature is a constant -- with another ringer: you need absolute temperature...

MikeAmann

I will take the extra credit - - - - because I have gauges.

Jamie is correct - the precharged tank on the air side is 50 psi.
And then I put the tank into the system (water side) at 50 psi.
The bladder does not move. It would take greater than 50 psi to make the bladder move.
And when it does, that means that the water side pressure increased due to the expansion of the water being heated. On the air side of the bladder, the pressure has also increased by the same amount as on the water side. Heating the IWH from cold (60 degrees) to 140 raises the pressure on the water side to 80 psi. So likewise, the pressure on the air side should be 80 psi.

I will confirm all of this tonight.
We are going to figure this out once and for all.

EdTheHeaterMan

EBEBRATT-Ed said:

I don't claim to knwo how to calculate the pressure rise...

...Some of this expanded water goes into the tank increasing the pressure above 50 psi

How to calculate the "how much" and what the ending pressure will be is above my pay grade

Fun Fact: While teaching one day Hydronics seminars for EHCC in New Jersey, I came across this factoid while explaining the need for an expansion tank on a closed system. When 60°F water is heated to 240° water it expands about 5%. I don't know where I found this info, but I remember looking it up in a engineering manual just to verify the fact, so i would not be questioned by some random overeducated engineering type in the class.

This means if you have 100 gallons of 60° water under about 15 PSI of pressure, you could get that water to 240° and have 105 gallons of water. That is why you need an expansion tank.

Maybe if you only raised the temperature by say 90° to... say 150° you might have 2.5 gallons more water. I'm not sure if the expansion is linear or curved as the temperature rises. I just know the 5% thing for sure.

EBEBRATT-Ed

So working backwards (which I am good at!!) 2 gallon expansion tank starting at 50 psi and the tank pressure is going to 80 psi after being expanded.

130abs gal/lb/sq"/divided by (80 +15)= 95abs

=130/95=1.36gallons of water that expanded into the tank?? Don't know if that is right

I can honestly say I never heard of gallon lbs/sq inch LOL

Jamie Hall

Good show! Except that the 1.36 gallons is the air left in the tank, not the water put into the tank. The latter would be .64 gallons. But that's the idea, for sure!

I never hear of gallons lobs/sq inch either -- but so long as you keep the units consistent on both sides of an equation... whatever works!

MikeAmann

Good info guys.
OK, I did the test, but I am questioning the results.
I will do the test again at a later date.

50 psi pressure cold
IWH tank water 68 F
IWH coil water 64 F
Heated tank water up to 140 F, pressure rose to 72 F.
Captured just shy of 2 quarts of water due to expansion (72 to 50).

When I refilled th system with water after installing the new controls, the water was colder, and the gauge rose to 80 psi. But I wasn't doing these tests at the time, so no measurements from then.

EBEBRATT-Ed

@MikeAmann

So you had 2 quarts of water with a pressure of 72 psi. I had figured (with @Jamie Hall help)


That at 80 psi you would get.64 gallons

So that is a match. .64 versus .5 gallons that you have with an 8 degree difference in temperature.

So in fact I redid @Jamie Hall formula using the 72# pressure and it comes out to 130/(72 +15)=1.49


2 gallon tank =2-1.49=.51 gallon which exactly matches your 2 quarts.



So if you want a lower pressure you need a bigger tank

MikeAmann

Awesome guys, I love it when the math verifies what is happening in the real world.

The reason that I am concerned about the increased pressure is because the boiler is old.
But now I know for sure that the expansion tank is doing it's job as far as giving the water someplace to expand to. I will simply remove the SharkBite check valve and that will solve the pressure increase issue, because then the water will push back against the street supply.

pecmsg

No it won’t and NO it can’t. 

MikeAmann

@pecmsg
The house has 110 psi CW supply and a PRV set at 50 psi.
The gauge has been installed for years and always remained at the 50 psi set point.
It wasn't until I installed the IWH and added the check valve that this issue started.

The PRV (regulator) does not completely block the reverse flow like a true check valve does.
My cousin lives 2 streets away from me and I installed a PRV for her.
Hers also works exactly the same as I described above.

Jamie Hall

Nope. Sorry. Your domestic water -- at 50 to 70 psi -- cannot "push back" against the street pressure. No way.