Pressure in a hydronic heating system

[Doug Miller]

Nope -- you didn't check the link he provided. The FillTrol is expansion tank and pressure-regulating fill valve in one unit. The air pressure in the tank bladder is what regulates the system pressure.

Phooey. He HAS to drain the FillTrol tank, at a minimum -- and since his problem is that the system isn't full, he can't possibly avoid admitting fresh water to the system. He doesn't have enough water in it. There is _no_way_ to fix his problem without admitting fresh water.

In any event, as soon as the oxygen that's in the fresh water is used up, there won't be any *additional* corrosion. The real big corrosion problem in hydronic systems comes from the *continual* admission of fresh water in the case of a slow leak (which is why it's recommended to close the fill valve once the system's full).

[Speedy Jim]

Yes, I did check the link.

The fill valve (regulator) is adjustable to set the boiler pressure. The boiler needs more _water_. You won't get more water by adding air to the exp tank end of things.

[Speedy Jim]

Apologies. I misunderstood what was being said.

Although the instructions state that FillTrol must be empty, I'll wager that simply pumping the air pressure higher will admit more water and raise the boiler pressure without draining any part of the system.

[Doug Miller]

Then you apparently didn't understand it.

*System* pressure.

Incorrect. Being on the bottom of the system, the *boiler* is full of water, and doesn't need any more. It's the *radiators* on the fourth floor that need more water -- and they aren't going to get it until the static pressure in the system is raised to at least equal that 38- to 40-foot head.

[Marilyn & Bob]

I hope you are right, Jim, I don't want to drain anything. I think that the simplest way to get an answer as to whether or not the system needs to be drained is to e-mail the manufacturer. If they are responsible enough to answer, I will know what to do. If I do have to drain the boiler, I will come back here for advice. I have modern shutoffs on both sides of the circulator pump and I have two ancient (I assume original to the system,

75-90 years old) shutoffs that seem like they would insulate the boiler from the system piping. I'd seek your guidance on what should work. Hope I don't need to do that.

In any case, it is not much effort to drain the standard expansion tank. I can shut off the connection between the system and the tank and then drain the tank and reopen the connection.

[Marilyn & Bob]

I e-mailed the manufacturer over the weekend and go a response first think this morning (terrific service). They said that there was no need to do anything except shut off the makeup water and removing the pressure on the system) before precharging the system to 17 or 18 lbs. Since I have the second expansion tank in parallel, it looks like simply allowing the boiler to cool off (and shutting the water intake) will satisfy the requirement to relieve pressure on the system.

Thanks again for your help.

[Doug Miller]

You might want to double-check this with the folks at Amtrol, but, to me, "removing the pressure on the system" means exactly that: *no* pressure above ambient, i.e. *zero* psig. Shutting off the water intake, and allowing it to cool off, reduces the pressure to the 12 psig precharge that you already have, not to zero.

At a minimum, I think you're going to have to *also* open the bleed valves on the top-floor radiators before you'll be able to get the pressure as high as you need to -- otherwise, you're going to be trying to compress the air in those radiators, too, and I think that won't work too well.

[Edwin Pawlowski]

Or open a drain valve near the boiler.

[Doug Miller]

Well, he's going to need to open the bleed valves on the top-floor radiators sometime, anyway, in order to get the air out of them -- might as well do it at the start.

[Dave Martindale]

This might not matter. If the control is currently regulating at 12 PSI, that means that the pressure tank under the control is essentially empty of water at 12 PSI. Add more air, and you're adding air to about the same volume of tank as you would with no pressure on the system. It's probably not as accurate as dropping the system to zero pressure, but that's going to require draining everything above basement level.

This shouldn't matter at all. Once the makeup valve is adjusted to regulate at 18 PSI, it will let it water until system pressure is 18 PSI, period. It doesn't matter whether there is air trapped in the top-floor radiators, since it will compress that air until it reaches a few PSI (whatever pressure is left after the pressure drop due to height). Then, at your leisure, you can open the bleed valves on those top-floor radiators, and the makeup valve will supply additional water to replace the air that escapes.

Dave

[Marilyn & Bob]

Thanks, that makes sense to me, too, especially since I have a second normal type expansion tank in parallel. I waiting for my light duty Campbell Hausfeld 3 Gallon Air Compressor to arrive (always can use a new tool) and I'll make the adjustment.

[handydave]

handydave had written this in response to

: Hey Doug, Great advise on Hydronic systems. The math will never fail you when you get into problem.

I had a system that was bugging me, very little heat to the third floor. The return line had been abandoned and a new line was run overhead. By measuring the height of the system from basement to the top of the return line I found I was 3 pounds off on the fill valve.

I now have all radiators working and my return pump sounds much better. Always check the math and use a new gauge to verify if the system gauge is reading correct.

Another "c> In article ,

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[bud--]

:

Might have been great advice, but another idiot post to a 3 year old thread from the sucko company.

You are posting to a usenet newsgroup. The sucko company is a parasite.