1 pipe steam main up and over hallway

SGM55 · November 2017

I have a 1 pipe steam main 4" which runs up 28" vertical up and over a hallway then horizontal for 8' then drops back down 28" into the next basement space
The first elbow facing up has a drip at the bottom which runs parallel with the steam main to get it out of the wall space. This then drops down 8" has a tee, and drain valve. off the tee bull we have a inverted trap that rises about 14" its just below the bottom of the steam main. Then drops straight down into the wet return
The steam line is pitched towards the first elbow with the drip and during cold start up appears this elbow and some of the upstream steam main is filling with condensate and not draining back into the wet return thru the inverted trap
I can open the drain at the bottom of the inverted trap and take out 10- 15 gallons of burning hot water before the steam starts going over the hump into the next basement
The drip and inverted trap remain cold
Also when the boiler builds some pressure say 1 PSI it appears to blow the condensate out and steam will flow, however by this time the rest of the building is getting warm and the boiler is shutting off
its a 28 flat and there are maybe 8 radiators off of this main they dont get any heat until close to the end of the heating cycle
There are no waterline problems at the boiler
The drip and inverted trap piping was replaced last year by another contractor
I am told these 8 radiators stopped working several years ago, and am new to this building which i have no history on
Any ideas?
Thank you

KC_Jones · November 2017

I think pictures would help a lot in this situation.

MilanD · November 2017

Wow... had to read this 3 times... pictures would help.

Sounds to me like that main is holding condensate and that the drip/false waterline/p trap return is either plugged up or does not give enough height for water column to overcome the p trap until the pressure builds. I am not getting how can the pressure blow through into a wet return without some kind of vent somewhere.

Questions:

1. the drip from the 1st ell going up - how far down does it go before turning back towards the boiler, and that 8" down and 14" up to just under the main? - in my mind it looks like a giant p trap with some horizontal section run parallel to main (say 6" below), then down 8" and back up 14" and then again back down into the wet return.
2. What size is the drip? Anything smaller than 1" would be a no-no on returns, and bigger would probably be better on a 4" main.

My guess is that the contractor who replaced the drip did not make it the same as the one now there. Built up pressure blows through it with psi overcoming obstruction of the piping, somehow - without a vent on the wet return side.

It may be as simple of a fix as repiping the vertical 14" and maiking it 8". If it truly terminates into a wet return, you may not need a trap there at all and can go straight down into wet return without a p trap piping.

How high is your wet return? Is it at the floor?

jumper · November 2017

>> then drops back down 28" into the next basement space<<
how does the condensate return from the bottom of this down 28"?

MilanD · November 2017

jumper said:
>> then drops back down 28" into the next basement space<<
how does the condensate return from the bottom of this down 28"?</p>

I'm thinking - it's probably parallel flow main from there and terminates at the end somewhere into a wet return...

SGM55 · November 2017

The drip out of the elbow is a close nipple and elbow before it parallels back with the steam main just enough to get out of the wall then it drops down into a tee and drain.
It is 1-1/4" pipe
These dimensions are the same from 100 years ago

It is indeed a large inverted trap, i would assume to keep steam out of the return
The dimension of the inverted trap may have changed I dont know what was there before
When the pressure builds we here a short blast of water hammer then the main clears and steam moves over the hump into next basement
dont know if condensate is blowing over the hump or into return
The inverted trap never gets hot enough where you cant keep you hand on it
In the next basement the steam main continues this is were the radiators dont work feeding up to 1st 2nd and third floor
then The main ends- main air vent present and working then drops into wet return
Wet return located within 10" of basement floor
Every other radiator works in the building, no problems with boiler water line
The bad radiators start to work after we drain the water out of the first elbow facing up
The problem is in that inverted trap- water seal- what ever one may call it thing, it may not have been plumbed back in like original, but is not plugged
One thing I forgot to mention is at the top of the riser where it goes over the hallway we can see there is a radiator take off hard to see but its there
Im assuming I need a vacuum breaker or air vent in the top of the inverted trap thing to make the condensate drain
I am assuming at lower pressure the falling water to the return may cause a vacuum in the inverted trap ceasing flow
Ill post pictures when i go back there next week
They also added another drip in the next basement off the bottom of the main with a bucket trap and line back to wet return which as far as im concerned does nothing

Jamie Hall · November 2017

It will help you, while we wait for pictures, to think like steam and condensate and air. Water -- condensate -- will only run down hill, unless you have a pump. Is there any way for the condensate to return by gravity with no pressure from the steam pushing it to the boiler? If not, you are going to have to provide one. No options.

SGM55 · November 2017

It is true wet return and were thinking of piping straight into wet return without the inverted trap, but the horizontal run (12") out of wall would suffer water hammer ? before dropping horizontally to wet return?
Believe that is why inverted trap is there to keep all the 1-1/4" pipe under the main elbow looking up filled with condensate to prevent water hammer

Jamie Hall · November 2017

SGM55 said:
It is true wet return and were thinking of piping straight into wet return without the inverted trap, but the horizontal run (12") out of wall would suffer water hammer ? before dropping horizontally to wet return?
Believe that is why inverted trap is there to keep all the 1-1/4" pipe under the main elbow looking up filled with condensate to prevent water hammer

I doubt you would get any hammer on that horizontal run. There is no velocity in it.

SGM55 · November 2017

Thats what the plan is then re pipe straight in eliminate inverted trap thing
Thanks for all the comments
Please post if any other ideas
We dont touch anything old on Friday after 2 PM
I asked the customer to send some pics will post when i receive and figure out how to post

Jamie Hall · November 2017

SGM55 said:
It is true wet return and were thinking of piping straight into wet return without the inverted trap, but the horizontal run (12") out of wall would suffer water hammer ? before dropping horizontally to wet return?
Believe that is why inverted trap is there to keep all the 1-1/4" pipe under the main elbow looking up filled with condensate to prevent water hammer

I doubt you would get any hammer on that horizontal run. There is no velocity in it.

MilanD · November 2017

If it's a true drip on that first take-off ell that terminates into a wet return, you don't need a trap of any sort. Matter of fact, that's probably what's preventing the condensate to freely fall down into wet return and to stack properly (A vs B dimension). On the other side, that bucket trap is probably also an overkill and may also pool water impeding steam flow (collapsing it) before it has a chance to enter the rads that currently don't heat. Unless you need a false water line or are draining into a dry return, you don't need any traps, mechanical or piped on any drips into wet return.

SGM55 · November 2017

Thanks for the help
We decided to pipe straight into the wet returns
Understanding the wet return and A dimension, was at one of Dan's seminars- probably one of the first ones in 1980 something or maybe early 1990's- getting old can't remember
Ends up the customers other contractor is a relative
So customer is having a hard time believing me
But the way I look at it is the other contractor has been trying to fix this for 2 years and still does not work, the other contractor made the comment " the inverted loop is there to prevent steam from getting into the return" so we know where that is going.
They went as far as to start installing electric baseboard heaters where the radiators are not working

MilanD · November 2017

SGM55 said:

But the way I look at it is the other contractor has been trying to fix this for 2 years and still does not work, the other contractor made the comment " the inverted loop is there to prevent steam from getting into the return" so we know where that is going.
They went as far as to start installing electric baseboard heaters where the radiators are not working

Oh boy, good luck with that - it's hard admitting one's relative is not the sharpest tool in the shed.

EBEBRATT-Ed · November 2017

If it truly drips into a Wet return you don't need any inverted trap.

It's sometimes difficult to trouble shoot something that's 100 years old, boiler (and water line) have probably been changed, renovations and changes.

Sometimes instead of figuring out why they did something you just have to forget that and work with what you now have

Pumpguy · November 2017

The usual solution to this type of problem is to pipe in what is called a "Door Loop" around the obstacle, which in this case is the hallway. The attached file shows all the details.

I am used to seeing this on 2 pipe systems, but don't see why it wouldn't work on 1 pipe systems as well.

Hope this is helpful.

EBEBRATT-Ed · November 2017

The other way (somewhat similar is a loop seal. Drop down out of the drip to the floor and bring the other end of the loop back into the bottom of the steam main.

But, with a wet return you shouldn't need to

1 pipe steam main up and over hallway

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