2-pipe steam heating

JSPhil

We're replacing defective steam traps in a 75-yr. old school. It's currently heated by a 2-pipe gravity return system, and the traps hadn't been addressed in many many years. The maintenance man wants us to replace all the air vents on the radiators because he thinks they're bad. They are Dole #1933 vents (non-adjustable; 10# max. psi). I want to remove them and plug the radiators because I don't think they are needed. They look like they MAY be 10 or 15 years old or so, and I'm wondering if someone installed them to compensate for poor heating (perhaps due to the bad traps!). Are they needed or not? The old school may have originally been a vacuum return system years ago, but even then would it have needed the air vents? Also, shouldn't there be an air vent at the end of the main? I've seen diagrams of 2-pipe systems BOTH WAYS! Some with an 'end of the main' vent, and others without. Any help out there? Thanks in advance.

Steamhead

Venting 2-pipe steam

You are correct. There is no need for vents on the radiators with this type of system- especially if it had vacuum returns. See if you can get a quantity discount on 1/8-inch plugs.

In a 2-pipe system with traps, the air and water leave the radiator thru the trap. The trap closes when steam reaches it. The water and air go thru the dry (above the waterline) return to a point (usually near the boiler) where the air leaves the return thru a vent (or vacuum pump if so equipped), and the water goes into the boiler. Bad traps will either stay closed, keeping air and water from leaving, or stay open allowing steam to enter the dry return where it will bang.

The burning question here is- was this once a vacuum-return system? I'll bet it wasn't, since it's working by gravity now. But you might want to check the capacity of the returns against those listed in "The Lost Art of Steam Heating" (available on the Books and More page of this site) to be sure. Vacuum returns could be smaller because of the greater pressure differential caused by the vacuum. If the original blueprints are available you could check those too.

See if you can find any manufacturer's name on any of the original radiator shutoffs, trap bodies or any unusual-looking equipment around the boiler. Also take some pictures and post then if you can. This will help us identify the system.

If your steam mains aren't vented, they need to be. This will make a BIG difference in quick steam distribution and lowered fuel consumption. Assuming this isn't supposed to be a vacuum-return system, you can drill and tap the pipe near the end of the main to add vents. Measure the length and diameter of the steam mains, and we can tell you what vents you need. Also make sure the dry returns are properly vented.

You do not necessarily need to completely replace the traps. Tunstall (www.tunstall-inc.com) and Barnes & Jones (www.barnesandjones.com) make replacement innards for most traps. This means you don't have to remove the existing trap bodies. Both companies have online catalogs.

Let us know how you do! Where is this job located?

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Dale

End of the main

I would also get a copy of Dan's lost art book to see what you have. I think there should be an F&T trap at the end of the supply main which will get some air out and most definately should be repaced along with the rad traps, and a nice big vent at the end of the dry return. This is the common design and your's could be different.

steve_6

steam traps

you need to check and see if these are water seal traps or thermastatic. If they are water seal it is rare that they would be bad. They don't have any moving parts to go bad inside them. Sometimes they just need to be washed out. Someone put air vents on the radiators because steam got into and pressurized the dry returns. If you have water seal traps and you get steam in the dry return, your pressuretrol or preferably vaporstat is set to high,causing the steam to blow right through the water seal traps.If they are thermastatic you need to test them and replace the capsules on the bad ones.