Two pipe filling with water

quack24

Hi all

I recently changed a steam convector to inch and a quarter baseboard with a trv I am having a problem that the baseboards are filling with water 
It's a two pipe steam system with no traps all returns are dropped down to a wet return 
The new baseboard contraption is sloped away from the trv

quack24

Here's a drawing

JUGHNE

If you take the control head off of the TRV so it is always open does the unit still retain water?
When the TRV closes it may create a vacuum that will not allow the water to drain.
Can the sensor feel the room temp or is it feeling the temp inside the convector?

quack24

I never put a control head on yet as I didn't get around to ordering it yet so it is always open

Jamie Hall

If the outlet drops to a wet return, the baseboard must slope in the direction of the outlet -- not the inlet.

And I presume that there is a steam vent on the baseboard?

I presume, also, that the TRV is on the vent, not on the inlet pipe? If you put the TRV on the vent, when it closes a vacuum will form in the baseboard until the steam vent opens, and hold water.

This type of arrangement must be treated as a one pipe radiator (or baseboard) which happens to have a separate condensate return line. From the standpoint of heating dynamics and steam behaviour, it is not a two pipe arrangement.

quack24

Thank you Jamie

The trv is on the supply and they are sloped forwards the return outlet not forwards the supply

Correct there is a steam air vent as depicted in the drawing as a lollipop with imaginary steam leaking out of it

markdelzell

sounds like a vacumn breaker needed on return loop

quack24

Here are some pictures

Jamie Hall

Indeed. You will have to have a vacuum breaker in addition to the steam vent -- or put the TRV on the vent where, since this is really one pipe steam, it belongs. As it is, your TRV closes off the supply at some point, but the vent is shut by temperature, and will remain that way for quite some time (many only reopen below 140 F). The steam condenses, and creates a powerful vacuum. This sucks water up from the wet return to occupy the space. Now you have a problem...

quack24

The vent never closes and when I remove the vent water gurgles out

Jamie Hall

quack24 said:

The vent never closes and when I remove the vent water gurgles out

Gurgles out of the vent? Or out of the radiator? Makes a difference.

It is possible that the vent is failed closed. Take the vent off. Hold it upright and blow through it -- it should allow air through freely. Now turn it upside down and blow. Most vents have a float, and when you turn it upside down the vent should close and you shouldn't be able to blow through it.

It's perhaps worth noting that a vent which is closed on temperature (steam) will not open under a vacuum, in general.

quack24

The water gurgles out of the radiator as if it is full of water making me think the return is clogged

quack24

The vent is not failed closed

I have ran it for a full cycle with the vent removed and water bubblesmout of the radiator
It should be noted only the top row gets hot the bottom one only gets warm about half way across

Jamie Hall

quack24 said:

The vent is not failed closed

I have ran it for a full cycle with the vent removed and water bubblesmout of the radiator
It should be noted only the top row gets hot the bottom one only gets warm about half way across

the bottom one only getting warm halfway across -- and water bubbling out of the radiator -- both indicate that the radiator simply isn't draining properly. It's rather uncommon for drips to get clogged, but they do sometimes. With the boiler off, can you undo things enough to simply pour water into the return to see that it drains freely? Oh... second look at the picture. It's all soldered together. How handy. It may also be that that condensate return line is simply too small and too flat to drain properly (it is, both, but sometimes one can get away with that).

I'm sort of grabbing at straws here, but another possibility is that the boiler pressure is high enough to hold water up that far in the drip -- but I would think you would have noticed problems from that elsewhere.

I don't think, now that I have more information, that a vacuum breaker is going to help. There is some other problem there which needs addressing.

jumper

I don't understand this thread? Why doesn't water & air go down the return?
Why air vent? Water and air are supposed to go down in steam system.

quack24

It's not a big deal I can put a union on the drip to see if it drains and to see if it gets hot all the way while drinking to a bucket

JUGHNE

The way I understand it, the return drops down into a wet return. So the air has to get out somewhere.
This resembles a 2 pipe vented set up with individual?? (we assume) drop to wet return.

I agree with Jamie that the return looks small and not much slope to drain.

Do we know what the operating pressure is?

quack24

Ok I opened it up and put a union on the return 
The water seems to be draining

I think what is happening is it partially fills up with steam as the steam collapses it form a vacuum ( which you can feel by air getting pulled in from the vent hole) the vacuum pulls air in the supply and the vent but mostly from the vent causing it not to fully heat up

I am thinking if I replace the trv with a regular gate valve I will be able to supply it with more steam and heat it all the way 
Please let me know if this thinking is correct

EBEBRATT-Ed

@quack24

What kind of pressure are you running? Try lowering the pressure. You probably have water backing up from the return which it will do if the pressure is too high

The other thing to try is a seperate return from each row of convector to below the water line of the boiler. Steam pressure in the bottom convector will cause the upper convector not to drain

retiredguy

Remember this, I have rarely worked with residential steam with pressures in ounces so correct me if I am wrong. Most every small commercial building we serviced or even installed that utilized steam maintained boiler pressures at 5 PSIG +or-, or lower with a vacuum return system.

According to a slant fin table, 1 1/4" copper finned tubing (EM-5) has the capacity of about 1720 BTU/FT. I am guessing that @Quack has about 20' of fined tube. So, 20' X 1720 BTU/FT = 34,400 btu. Thus 34,400 BTU divided by 970 BTU/ lb of steam =35# of water, which divided by 8.33 = 4.3 gallons of water. That seems to me to be a lot of water to drain through a 3/4" almost horizontal line return line at close to zero # pressure or even at a slight vacuum due to the steam condensing. My guess is that a standing cast iron rad job would work but finned tube radiation with almost horizontal radiation will not work at steam pressures that low since there is too much resistance to condensate flow. My 2 cents.

Jamie Hall

Your arithmetic is fine, so far as it goes -- but remember that that rating is in BTUh, so the water output is in gallons per hour -- less than a tenth of a gallon per minute (that's one of the beauties of steam -- the actual quantities of water on is playing with are remarkably small!). A 3/4 inch line should handle that -- provided it has enough pitch and no sags. It won't take much of a sag, or inadequate pitch, however, for the water to pool -- and then you do have a problem.

retiredguy

@ jamie hall, my thought was to how much condensate is produced on a cold or cool start up and as to how much condensate will pass through that return line at close to zero pressure. The gallons I show is on a total of 1 hour but still that is a lot of water for what looks like a 3/4" horizontal line.

The company I worked for once replaced a wet return loop with a float trap that dumped into a condensate return tank. The engineer sized the replaceable orfice using 3 psig as the pressure across the orfice and figured that it was large enough to handle the whole radiation load. It worked well until the boiler shut down and the pressure dropped to near zero, then the system flooded with water. We replaced that orfice with one sized for gravity flow or zero pressure and everything worked well. I would be curious as to how that radiation would perform with a 3-5 psig steam operating pressure. One option would be to cut the return line near the downstream solder joint, install a shut off valve for safety and see how much water flows out and how the radiation heats. Your thoughts?

EBEBRATT-Ed

@retiredguy

Don't forget that would be 4.3 gallons of water/hour. Less than a 5 gallon drywall bucket. Should be ok with 3/4". But it is funny looking and looks like a few dips.

Either vacuum is keeping it from draining or his steam pressure is to high causing the vent not to work right and condensate stacking in the return at 28"/lb of pressure

ethicalpaul

How can vacuum keep condensate from draining if pitches are correct and valves are open?