Two pipe steam repair

John Taylor_2

Looking for some help with a two pipe system for one of my customers.

It looks like a contractor some time ago replaced and relocated the original steam boiler. It is (or was) a two pipe system with convention thermostatic radiator traps (traps are still in place) and no radiator venting. It appears (although all the evidence evades me) that the original boiler had a wet return buried in the concrete floor (or at least that's what I surmise). They must have abandoned all the old wet return and tied the dry return together with the steam main (piping at the ends is newer) like a one pipe system is designed with vents at the end of the "former" dry return by the boiler.

They obviously have live steam in the old dry return and the vents must close rather quickly once the steam reaches them, thereby closing any air venting in the entire system. It puzzles me how this system can even heat without proper venting and the customer does experience hammering at the radiators (which doesn't surprise me).

So my questions:
1. How on earth does this even heat (I wasn't at the site long enough to watch it cycle)
2. How to return it to it's original two pipe glory?

I know I need to separate the mains (they go off in two directions) and the dry returns, but dripping the main then becomes a problem due to doorways and a good route back to the boiler. Traps and a pump station I suppose would be one answer but I'd like to avoid pumps if possible. Can I route a drip back below the main to the boiler area and rely on the water seal at the boiler return piping (without the need for a trap)?

nicholas bonham-carter

Can you draw a diagram of the layout for us to see? And we love pictures!
See how the air can get out as steam is made-good traps are essential, unless this is trapless, in which case orifices would be used to limit the amount of steam entering the rads to just that amount which can be condensed, at maybe 2 ounces of pressure.
Definitely avoid pumps and auto feed like the plague, if at all possible.--NBC

Jamie Hall

Would I presume that the returns from all the radiators empty into the dry returns still? That hasn't been messed up? Then the next question is... are the dry returns below the steam mains? And do they pitch back to the boiler?

If the answers to those questions is yes... then I would be very seriously inclined to uncouple the dry returns from the steam mains, and set it up so you have crossover traps set so that they can accept both condensate and air from the steam mains, draining into the dry returns. The dry returns will need venting -- as they do now (that's where the air from the radiators goes, after all!).

But as NBC says, a diagram would be helpful...

John Taylor_2

Yes, rads still tie in as they should but the end of the steam main and the beginning of the dry return are level if I remember. The main may even be a bit lower than the return at that point. And yes the return does pitch back.

Yes, proper venting is a given.

Just a thought, could steam main pressure be utilized to "pump" the condensate up a short way into the dry return?

John Taylor_2

Come to think of it regarding my last comment about using steam pressure. I can't think of how it could be piped without causing hammer at the trap.

nicholas bonham-carter

Unless the building has settled, I am sure the pipes are sloping back all the way from the boiler, all around the building, to the wet return, with proper slope, (at least I hope so).
The radiator, and crossover traps need to be working to let the air out. Is this the case?
Some old two-pipe systems had no traps, and instead relied on orifices in the steam inlet valves to limit the amount of steam into the radiator to only that amount which could be condensed.--NBC

Steamhead

I bet that system never had wet returns. If the end of the steam main is above the end of the dry return furthest from the boiler, there was probably an F&T trap connecting the two. Condensate and air were thus drained and vented into the dry return.

Most of the systems I've seen with this configuration are Webster. Check the radiators to see if they have their original Webster valves and traps on them. If so, this might confirm it.

John Taylor_2

Hi Steamhead,

The end of the main is even with or below the end of the dry return (I called it the beginning previously as the direction of flow in the return is toward the boiler). At the what looks like the old boiler locations is a capped pipe coming out of the floor. I assumed it to be the old return but honestly don't know.

I'm going there tomorrow, I'll report back with more details.