water is flowing backwards from condensate line and filling the radiator with water?

rhodebump

I have a three radiators in one classroom that are not heating (2nd floor). It's a two-pipe system, and I replaced the steam capsules in each of the traps of the radiators.

I turned up the boiler and opened up one of the traps. While a little damp, there wasn't water. There was a vacuum coming from the condensate line. Then a minute later, water started gushing out of the condensate line. I put the cap back on the trap and heard the water gurgling into the radiator.

Here's picture of one of my traps (in case I was not clear)
What can cause water condensate to flow backward?

Thanks you! The picture is with a heat camera

Long Beach Ed

Pretty color. You could have a failed trap that is passing steam into the return. That steam pressure may be be blowing the condensate out. How are the rest of the traps downstream?

neilc

do we know what the steam pressure is?

rhodebump

Steam pressure is 1.5, not high

JUGHNE

Is there a transfer pump somewhere in there?

Or is there another floor above this and is there a attic overhead steam main that used downfeed risers?

Gordo

@rhodebump : If I understand you correctly, you are saying your steam pressure is 1.5 psi? If so, that may be 3x too high for a two pipe vapor system. Vapor systems generally run best at 1/2 psi max.

rhodebump

@Gordo I made a mistake. Our vapostat is set for 1 PSI and 12 oz for the diff. I forgot it was "subtractive"

rhodebump

@JUGHNE This is on the ground floor, there are two more floors above. There are pretty sure there are no pumps in the system.

JStar

From the picture, it looks like the radiator is getting hot. Are they working since you changed the trap elements?

The vacuum is likely caused by water flowing through a return line, or steam condensing in a radiator or elsewhere. A return may also be trapping condensate somewhere due to sagging pipe/hangers.

JUGHNE

Is this a downfeed steam system with the main above the radiators?

Also you have 2 floors of return water from above that probably shares the return drops. That line may not be free to drain.

Or I have seen a add on transfer pump in another part of the building that was returning condensate into the return piping, which was too small to handle that flow, it should have went back to the boiler room, but it was coming up in trap piping.

AMservices

Recently had a very similar experience.
1 radiator out of 20 wasn't heating.
As soon as I take the cap off the trap, condensate vomets out coming from the dry return.
Took me awhile to figure out what was going on. Then it hit me, high pressure goes to low pressure, always.
When I took the cap off, that became the easiest way out for the air. The only other option for it was 100' away. So the air pushed condensate backwards and lifted it right out at my face.

The reason this radiator was not heating is because theres a problem with a f&t trap at the end of this main. It's to big for the amount of condensate it needs to handle or it's not venting and draining properly.
Follow your piping, inspect the pitch, make sure the air can vent from the mains leading to your radiators and the condensate isn't trapped somewhere.

Jamie Hall

And make sure the dry return is also adequately vented!

rhodebump

I replaced two f&t traps (crossovers)

The radiators are still not heating up. Cracked the trap on it, and while no water, air is just gushing out of the condensate side (not the radiator side).

Measured my one main. The building is 90'x60', 3 floors, no basement

1st Main is 5" OD, 128' long
2nd Main is 4" OD, 60' long

I have 2 Gorton No. 2 air eliminator vents and 1 Hoffman 75

Does anyone think I am air-bound with those 2 Gordon #2's?

Jamie Hall

The Gorton #2s should be getting rid of the air. F&Ts are not crossover traps. Completely different application and operating principle. They can serve as vents.

Clearly the dry return to which that problem child trap is attached is not being vented, or if there is a vent on it, it's being closed by steam from a nearby failed trap (or is failed) or the air can't reach the vent. Follow the whole length of that dry return and see where the vent(s) is (are). Check the return for sags which might prevent air from reaching those vents.

With mains that size however, you are going to need more venting than just those 2 number 2s.

rhodebump

Last thought, could I just temporarily remove all air vents (open pipe) and see if the problem children (aka radiators) heat up ?

rhodebump

Thank you for the advice @Jamie Hall !

For the crossover traps, as I understand, these allowed air to be vented from the steam main to the condensate line. The crossover traps used the same type of traps that I have on the radiators, but due to pipe configuration, I don't think the crossover trap would get any water, just air.

When I repaired the crossover traps (here is a pic), I installed a new thermostatic disk. I think this was the correct thing to do, but I am a little worried after hearing that crossover traps are a different beast.

Should I have used something different than replacing the thermostatic disk in the crossover trap?

Thank you.

Jamie Hall

Nope -- perhaps I confused you My apologies. Crossover traps and radiator traps are exactly the same (sometimes different sizes). The crossover trap does sometimes seem to baffle people, because it's above the steam main. The secret is that all it does is vent the air from the steam main into the dry return. Any condensate present is taken by a drip to the corresponding wet return; there is also -- almost always -- a drip from the end of the dry return to the wet return. It is essential that the wet return at that location really be wet all the time! The connections must be below the static water level in the boiler. Crossover traps are not intended to carry any condensate at all. That goes down the drips.

What you are referring to as the condensate line does, yes, carry condensate from the radiators -- either to the drip noted above or back to a drop at the boiler (some go one way, some the other). Of at least equal importance is that the dry return also carries all the air from both the steam main and the radiators to a vent or vents -- often clustered at the boiler before the dry returns join and drop to the boiler. If the dry returns aren't vented, all kinds of problems happen -- like no or very poor heat.

rhodebump

Can I remove a plug from my air vent antler temporarily to see if this allows the heating radiators to work?

AMservices

> @rhodebump said:
> Last thought, could I just temporarily remove all air vents (open pipe) and see if the problem children (aka radiators) heat up ?
You can, but I would recommend putting a ball valve on top so you can close it quick if condensate starts shooting out