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1933 Trane Two Pipe Steam Convectors

First of all, thank you to everyone for making the wall such a great resource. I have been diving into more steam heating work recently and have learned so much with your help.

The job I'm having trouble with is in a 1933 house with Trane two pipe steam convectors. As I understand it, these convectors contain some kind of orifice or other design to act as a steam trap. Unlike other houses I've seen with similar convectors though, these have all had individual steam vents installed. This strikes me as extremely odd, and doesn't match any description in Lost Art or old Trane literature. This was done at least 5 years ago.

First question: should these convectors have individual air vents? The supply and return mains both have main vents (Hoffman 75s) as well.

The big issue we're having is water hammer that is getting worse as the season goes on. At first it seemed to be coming from one first floor wall/ceiling but is now audible throughout the house. This is not the first year the customer has lived in the house so appears to be a progressive problem.

Some observations I've made:

1. The near-boiler piping is definitely not well done (neither supply nor return).
2. The steam piping has had its insulation removed.
3. The system runs on a pressuretrol set as low as possible, but not a vaporstat.
4. The return pipes from several radiators feel extremely hot, as if they're carrying steam, not just very warm condensate.
5. I can hear the main vent on the return venting, but I don't hear anything from the main supply vent.
6. There was a sag in the return piping as it runs across the basement that I have corrected, which didn't solve the noise issue.

Second question: with so many potential issues with this installation, where should I start?

Again, thank you all so much for your help!


    JUGHNE Member Posts: 11,061
    Operating pressure is always a good place to start.
    If there are fixed orifices in the valve union they would have been sized based on operating pressure.

    Could the pressure be creeping up over time?
    Plugged pigtail?
    Low pressure gauge??
  • Jamie Hall
    Jamie Hall Member Posts: 23,286
    If you are feeling steam hot returns... problem. And it probably is operating pressure -- which needs to be limited to probably no more than 8 ounces max. Without a vapourstat... you're going to need a low pressure gauge and a vapourstat.

    There really shouldn't be vents on the convectors, but they may not be actively hurting anything. My guess is that they may have been put on to correct the problem with the sag in the dry return, which would have killed steam delivery to any convectors beyond the sag. The vent on the main probably closes very quickly, which may be why you don't hear much from it.

    If there was a sag in the main dry return, odds are pretty good that there are sags or settling in other pipes as well -- and that is where I would start looking for the hammering. Near horizontal pipes buried in the ceiling of the first floor are known villains, and it doesn't take much.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • drewsherlock
    drewsherlock Member Posts: 2
    Thanks, guys! I have already cleaned out the pigtail. It was definitely plugged and I had high hopes that would solve the problem (alas). It is still possible the pressuretrol is not working correctly (or just incapable of controlling to 8oz), and the system is running at too high a pressure for the design. It sounds like installing a vaporstat would be a good place to start.

    Anyone else have thoughts? Trying to get my head around this problem before going back to the customer.
  • Steamhead
    Steamhead Member Posts: 16,835
    Are those main vents designed to hold vacuum? If they are Hoffman #76, they are. This worked great on coal, but nowadays they can hold water up in the system where it will bang. Depending on how long the mains are, I'd replace them with either Gorton #2 or #1 vents
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service