Two pipe steam with one tricky radiator

mygardenshed

I have a two pipe system and all is well bar one second floor radiator. Steam arrives near the radiator as I can feel it through the warm floor. That’s as far as it gets, This has been like this for almost as long as we’ve been in our house, 40+ years. This radiator has an 1/8” air bleed valve on it like what would be found in a hot water system.
Now the odd part. When the system runs and all radiators are hot this one is still cold until I remove the bleed valve and blow into the 1/8” port. It seems that little bit of back pressure clears whatever the issue is and the radiator then heats fine.
This one radiator had a leaky pipe, not sure if supply or return side about 30 years ago and it was repaired with a dresser fitting. I’ll repipe this in the spring when I do my wants, needs and changes on this new install.
Curious to learn why the back pressure has the effect that it does.
Thanks

JUGHNE

Just removing the vent may have allowed the air to leave.
You could have that trap stuck closed not allowing air to vent on thru.
But it must pass condensate if you do not end up with a flooded radiator.

Or steam from a different failed trap rises up there and closes that trap.
Is the trap body and piping hot before you remove the vent?

mygardenshed

JUGHNE said:

Just removing the vent may have allowed the air to leave.
You could have that trap stuck closed not allowing air to vent on thru.
But it must pass condensate if you do not end up with a flooded radiator.

Or steam from a different failed trap rises up there and closes that trap.
Is the trap body and piping hot before you remove the vent?

Sorry for the late reply.
I’ve removed the trap cage to see if any differences occur and things remained the same. Radiator was holding no water so the returns must be working as they should.
When I remove the air bleed vent and leave it off during a call for heat nothing happens. Only get a result after I blow in a bit of back pressure. My gut feeling is an almost fully clogged supply pipe.
I’ll open up the ceiling in the spring at the point where the dresser fitting is. The clogged area is more than likely the cause of the pipe rusting through.

Jamie Hall

It's really rare for a steam main to clog. On the other hand, it's unheard of to put a Dresser fitting on one. When you get in there to look at it, at the very least make sure all the pitches are correct -- and then replace that fitting with a couple of right length pieces of pipe and a proper union.

mygardenshed

Jamie Hall said:

It's really rare for a steam main to clog. On the other hand, it's unheard of to put a Dresser fitting on one. When you get in there to look at it, at the very least make sure all the pitches are correct -- and then replace that fitting with a couple of right length pieces of pipe and a proper union.

That’s my plan. I wouldn’t open the ceiling without the intent of doing a full repair.
Full disclosure: I’m the guilty party as far as the fitting goes. Very long ago, I didn’t have the knowledge I have now and I was a single parent with two girls to look after. Needed the leak stopped pronto.
Do you have a theory as to why this is happening?

Jamie Hall

Nope. And with two girls and single parenting, you're fully excused!

New England SteamWorks

JUGHNE said:

I’ve removed the trap cage to see if any differences occur and things remained the same. Radiator was holding no water so the returns must be working as they should.
When I remove the air bleed vent and leave it off during a call for heat nothing happens. Only get a result after I blow in a bit of back pressure. My gut feeling is an almost fully clogged supply pipe.
I’ll open up the ceiling in the spring at the point where the dresser fitting is. The clogged area is more than likely the cause of the pipe rusting through.

1. Not necessarily. If the radiator never heats, then there is no condensate to drain.
2. How do you "Blow in a bit of back pressure"? Doing so may temporarily disperse condensate, allowing either steam in, or air out.
3. Sounds like you have a water seal, either in the supply or the return.

Jamie Hall

This ^^^.

The fact that water drains does not mean that air can escape.

JUGHNE

New England......wrong quote....that wasn't me.

This one was:

JUGHNE said:

Just removing the vent may have allowed the air to leave.
You could have that trap stuck closed not allowing air to vent on thru.
But it must pass condensate if you do not end up with a flooded radiator.

Or steam from a different failed trap rises up there and closes that trap.
Is the trap body and piping hot before you remove the vent?

No biggie.

JUGHNE

tommay said:

If this is truly steam and you have a bleed valve on the radiator, that's the problem, you need a steam radiator vent. A bleeder type vent is for hot water and will not work with steam.

This is truly steam, and (read) the first paragraph that states that this is a 2 pipe system that typically has no vents on the radiator. The air bleed valve is not the problem. If closed it is as if it is not there.
Yes, an air bleeder vent is for hot water and might bleed air manually until steam arrives.
And some unknowing persons would put a steam radiator vent on this....it may help.
But there is still a problem.

It sounds as all other radiators work without any vent at all.

JUGHNE

The air should be pushed out by the steam entering, go thru the trap to an unpressurized return line.
When the steam gets to the trap that element would close the air opening.
When condensate gets to the trap and cools the element (relativity speaking) it then open for a bit to pass the water and then close when steam gets there again.
The return piping should only pass air and condensate water, never be pressurized, simply gravity flow of water and air thru a vent or cond pump vent.

If there is an enough of a sag creating a water pocket in the return pipe the air may not vent and then no steam enters.

mygardenshed

JUGHNE said:

tommay said:

If this is truly steam and you have a bleed valve on the radiator, that's the problem, you need a steam radiator vent. A bleeder type vent is for hot water and will not work with steam.

This is truly steam, and (read) the first paragraph that states that this is a 2 pipe system that typically has no vents on the radiator. The air bleed valve is not the problem. If closed it is as if it is not there.
Yes, an air bleeder vent is for hot water and might bleed air manually until steam arrives.
And some unknowing persons would put a steam radiator vent on this....it may help.
But there is still a problem.

It sounds as all other radiators work without any vent at all.

You are correct. All other radiators work as they should. No other radiators have vents. As this radiator has had a problem with a leaking pipe (supply or return I don’t know) in the past my instinct leads me to that issue.
For a few days this week I ran it with the trap cage removed and there was no difference.