Expansion Tank Pressure

1daveman

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I would appreciate some help with the installation of an expansion tank. This is used in radiant floor system, and the photo is attached. I am not sure how easy it is to see in the photo, it is attached to a spirovent on the intake side of my water tank.

I set the expansion tank pressure to 30 psi, and the system pressure was between 35 and 38 or so. When I heated the water, the pressure rose fairly quickly, I stopped at 55 psi while the temperature had only risen about 15 degrees.

I thought maybe I should add pressure to the tank, so when I connected the pump to the expansion tank, it still showed 30 psi. I would have thought it would match the system pressure?

Can anyone tell what I did wrong? I woyld appreciate some help.

Jamie Hall

Why is you system pressure so high in the first place? Most radiant systems run very comfortably at 12 to 15 psig cold, unless it is a very tall building.

OK.

Let us suppose that your desired system pressure is 15 psig — which I would recommend, unless there is a very good reason indeed to make it less.

Then the proper procedure for setting your expansion tank is to disconnect it from the system (if you have a valve between it and the system, this is a lot easier — otherwise you may have to drain the system. Sorry…) and then drain all the water out of it. Completely empty. Then using the Schrader valve, add air to the desired system pressure. then reconnect it to the rest of the system. If there is not autofill valve, add just enough water to bring the system cold pressure to 15 psig. If you had to drain the system, you may have to purge it…

Make sure, if there is an autofill, that it is set to the same pressure.

JUGHNE

What it the pressure of your pressure relief valve(s)?

It should have opened and dumped water, it may have but it looks to be piped thru the wall to where??

Usually best to have the end of the drop pipe in the same room where it would be noticed.

1daveman

Thanks Jamie

I will lower the system pressure.

This was a new tank. I replaced an old tank that was too small with this larger new tank. There is a valve in front of the old tank, so I closed the valve and removed the old tank. I then added more copper pipe from the valve to a new location. I then bleed the air out of the new pipe, added 30 psi to the expansion tank, attached the tank and opened the valve.

Should I have done something differently?

1daveman

Jugne.

Thanks for the comment. The PRV is 75psi, so I stopped heating the water before it got that high.

GGross

When you added 30 psi to the expansion tank how did you do that? You added air pressure to the air side of the tank correct?

1daveman

GGross

Yes using the Schroeder valve and an electric pump

hot_rod

sounds like you are running a tankless heater on main water pressure? The black tank what does it do? You are pumping out of it through a mix valve into the tankless?

1daveman

Hi Hot Rod

You helped me earlier with this system, and actually helped me determine the proper size of the expansion tank, which is why I am installing it.

The black tank is the hot water for my radiant floor system,. It is a closed system, and is heated by solar.

The tankless is back up in case the solar does not heat enough.

I added the dirt mag, larger expansion tank and mixing valves with this modification., based upon suggestions from this forum.

Everything works except the pressure is rising when the heat increases.

Any suggestions would be appreciated.

Thanks!

Dave

hot_rod

so what is regulating the pressure in the system with the exp tank? If you precharge the tank to 30 psi, fill the system to 30 psi and shutoff the fill valve. Now run the system and see how much the pressure rises.

Yes, the pressure will increase some as the water is heated and expands, 10 even 15 psi is still way below the 75 psi relief.

The expansion tank covers the hydronic and the solar? Or is there a coil in the black tank for the solar loop?

1daveman

The tank water is what is pumped through the floor, and there is a coil in the tank for the DHW. The expansion tank therefore is for water in the tank and radiant floor.

I started with about 35 psi and 73 -75 degree water. When the water got to 95 the psi was 55, so I stopped, as I will never get to 160.

When the water cools I will drop the pressure to about 15psi, but it is hard for me to belive I will be able to get to 160F, so I think something does not seem to be working correctly?

Does this make sense?

Jamie Hall

I still think you are running your [pressure much higher than it needs to be…

What you have is fine for domestic hot water, but not needed for heaitng.

1daveman

Thanks Jamie

As soon as the water cools down I will lower the pressures. However I am still convinced the pressure will rise too much. At the pressures I started with, it rose 20 psi for 20 F degrees. I don't think the expansion tank is working like it should.

hot_rod

raising the tank pre charge does limit its capacity, as @Jamie Hall mentioned, set everything at 12 psi.

But before you do lower the tank pressure down and see if you hear or feel water entering the tank. There have been instances of the diaphragm being stuck against the nipple and not allowing water into the tank.

1daveman

Thanks HotRod

That makes sense! I don't hear anything that would make me think water is going into the tank. I also would add that the system pressure was 55 psi but the tanks pressure was only 30psi, so I bet that is it.

So I assume I should disconnect the tank and somehow push in on the bladder through the opening, to release it?

hot_rod

if you just let all the air out start adding water pressure, sometimes you hear a dull thud of it breaking loose.

One tech here suggested he used a wood Dowell to free a stuck diaphragm

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1daveman

@hot_rod

Hey that worked. So far a 20 degree temperature rise and no change in pressure.

I let out all the pressure in the expansion tank, slowly added pressure to the system. As soon as I heard a noise. I closed the valve to the expansion tank and pressurized it back up. It now works perfectly.

Thanks so much!