2 pipe steam dry returns no traps

Dan C.

We are moving some pipes and Radiators on a two pipe steam system. Each radiator has a radiator valve on the supply and the return with no trap. The radiators also have vents on them. Some of the supply and return risers pick up more than one radiator. There are teo mains and at the end of each msin there is a loop seal. The homeowner says everything heats fine and is quiet. I’m trying to figure out if I should put traps on the stuff that we are doing or leave it the way it is. At some point before the next heating season we will be replacing the boiler and installing a vaporstat.

Danny Scully

Sounds like a 2-pipe air vent system, but maybe not. As always, pictures help...Do the returns connect above or below the waterline? Ideally in a 2-pipe air vent system, they would/should each drop individually into the wet return. But the loop seals you describe make me think it’s a orifice system that someone knuckleheaded. Again, pics please!

Dan C.

They do not drop individually into wet returns. Everything goes into dry returns which is why I thought there should be traps. No orifices. Just radiator valves in supply and return.

Dan C.

https://youtu.be/5N6yJ3-FcxQ

https://youtu.be/UWuZlCK7ILg

Couldn’t figure out how to post a video. I uploaded these on to YouTube.

Dan C.

pictures.

ratio

The picture on the right shows an air vent, along with two pipes. Looks like a two-pipe air vent, as read about in TLAoSH, also see here for radiator pics.

Dan C.

I have worked on plenty of two pipe systems with air vents. Never with dry returns. I’m trying to figure out if I need to do something different with the radiators and pipes we are moving. Either add traps or run them all individually and run a wet return.

JUGHNE

Orifice in supply valve union, maybe?

Dan C.

I don’t think so. But I guess I could check when we take the radiators out.

JohnNY

So, you're saying there's a common return main, dry, picking up multiple radiator returns, which then drops down into a loop seal? Is the return vented somewhere?

Dan C.

Correct John. Yes someone added vents to both returns. I don’t think they should be there. I was going to take them out when we do the boiler because the msins are vented and the radiators all have vents.

Danny Scully

If it is in fact a 2-pipe air vent system you’ll want to size your supply hand valve at least 1 size bigger then your return hand valve.

EBEBRATT-Ed

@Dan C.

You answered your own question" The homeowner says everything heats fine and is quiet. I’m trying to figure out if I should put traps on the stuff that we are doing or leave it the way it is."

Why mess with something that is working? Relocate what you have to relocate and copy what is there. You start changing things and open up a whole can of worms.

Jamie Hall

Dan C. said:

Correct John. Yes someone added vents to both returns. I don’t think they should be there. I was going to take them out when we do the boiler because the msins are vented and the radiators all have vents.

Don't do it. The dry returns are supposed to have vents. They may well be original, or replacements for the original vents. If any of the vents aren't where they should be, it's the radiator vents -- but the only thing that will harm is that the system is going to be an almighty bear to balance. Taking out the dry return vents will make that problem much worse.

As @EBEBRATT-Ed said, you are asking for trouble (he was gentler). The homeowner would tell you if things weren't working properly; they have a way of doing that.

So...

If ain't broke, don't fix it.

Dan C.

“Why mess with something that is working? Relocate what you have to relocate and copy what is there. You start changing things and open up a whole can of worms.”.
I don’t really want to change anything. I just want to make sure we don’t do it the way it is and then get blamed if there are problems.

I was going to remove the vents on the returns because I thought they would cause steam in the dry returns. If they need to be there then we will leave them. Thanks for the help.

Jamie Hall

Dan C. said:

“Why mess with something that is working? Relocate what you have to relocate and copy what is there. You start changing things and open up a whole can of worms.”.

I don’t really want to change anything. I just want to make sure we don’t do it the way it is and then get blamed if there are problems.



I was going to remove the vents on the returns because I thought they would cause steam in the dry returns. If they need to be there then we will leave them. Thanks for the help.

If you have steam in the dry returns -- which is quite possible, but not correct -- it is because somewhere steam can get from the steam lines, which it is under pressure, albeit only slight pressure, across to the returns, which should be under no pressure at all.

Things to check.

First, too high a pressure in the system as a whole. For most vapour systems, less than 8 ounces; Richardsons run a little lower.

Second, missing steam flow control on radiators -- if orifices, missing. If adjustable throttling valves, valve too wide open. If traps, trap stuck open. Richardson type devices -- too high a pressure and valves too far open.

If there are crossover traps, defective (stuck upen).

Third, drips to what should be a wet return which isn't. It's not uncommon out in the outer darkness to have both a steam main and a dry return drip to a wet return. It's also not uncommon for the water level to have been lowered, and that piece of wet return is no longer wet, allowing steam to swoop over.

Fourth, blown loop seals -- which goes back to pressure.

There may be more I can't think of at the moment.

Dan C.

Jaimie,
If I have no traps on the radiators and all of the returns are tied into dry returns, what is preventing steam from going into the return from one radiator and venting back against a return from another radiator towards that radiators vent.
Also, why do I want those vents at the end of the dry return? If all the radiators have vents and the mains are properly vented, it seems like the only purpose of the vents at the end of the dry returns would be to fill up the dry returns with steam.

jumper

Dan C. said:

Correct John. Yes someone added vents to both returns. I don’t think they should be there. I was going to take them out when we do the boiler because the msins are vented and the radiators all have vents.

Makes sense to me to eliminate redundant vents. Unless they're one way they they let air in as well as out. I would not add traps unless there's a reason to worry that steam in return will prevent condensate from draining.

Jamie Hall

First, unless you are sure that this is a two pipe air vent system, it's not. Two pipe air vent systems have one distinguishing feature which almost never gets knuckleheaded: the radiators have two valves, one at each end, and both at the bottom. And, of course, an air vent. They work in much the same way as a one pipe system -- and they are treated and vented in much the same way.

Now, having said that... if you look at the pictures, voila. A valve at each end of the radiator, both entering low, and an air vent. What do we have? A two pipe air vent system. NOT a two pipe vapour or later steam system. They are odd beasts, and were built in a sort of transition time, before traps or other widgets were made to prevent excess steam from getting into the dry returns.

Now that we've gotten this far... don't add traps. Those systems didn't have them (they weren't invented yet). The air vents on the "returns" won't hurt anything -- they'll let air out of the "returns" (they aren't, really, but that's semantics) which may help get steam evenly to all the radiators. If you don't like them for some reason, taking them out won't hurt much. Won't help, either.

On these systems, if steam makes it though one of the radiators, so be it -- it will happily go to some other radiator through the "return" where it's needed. And, as the homeowner said -- everything will heat well and be nice and quiet.

I would suggest before turning a wrench that you go look in the Lost Art for Dan's commentary on two pipe air vent systems...

Dan C.

I just read it now. I will keep everything the way it is and keep the vents at the end of the return. Thanks.

Dan C.

We are replacing this boiler now. I put tees for vents at the end of the returns and I want to plug them. If we need them I can just put them in after. The thing I don’t understand is why do I want to vent the returns? The mains are vented all the radiators are vented and I don’t want steam in the returns. If I vent the returns that pretty much guarantees I am going to completely fill the returns with steam.

Jamie Hall

Go back and reread the section on two pipe air vent systems. The returns really aren't, and it does no harm to have steam in them. The theory behind them (and it was a very good theory) was that by having a separate pipe the main function of which was to carry condensate, you'd reduce any hammer problems, maybe be able to use a size smaller pipe for the supply, maybe reduce the pitch... but it really didn't matter as the system really works like a one pipe system, only with two pipes, one of which is mostly supply and one of which is mostly return.

Put the vents back on the returns...

Dan C.

Got it. Thanks.

EBEBRATT-Ed

@Jamie Hall,
Thanks for this:
The theory behind them (and it was a very good theory) was that by having a separate pipe the main function of which was to carry condensate, you'd reduce any hammer problems, maybe be able to use a size smaller pipe for the supply, maybe reduce the pitch... but it really didn't matter as the system really works like a one pipe system, only with two pipes, one of which is mostly supply and one of which is mostly return.

Put the vents back on the returns...

The way you explained this is perfect. I just never thought of it this way. makes more sense to me now.
Ed