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help with loud two-pipe system

I recently bought a house with a two-pipe steam system.  There is one radiator that bangs, and I'm looking for ideas on what to do. 

I've read Dan's books and this site, so here are some of the relevant facts for my system:

- The radiator that bangs is the largest one in the house and the closest one to the steam boiler.  So the steam gets to it first.  The banging happens when the system is cold (i.e. in the morning when the heat comes up) and it occurs only until the trap in the radiator closes.  The problem appears to be getting worse with time (possibly as the temperature is dropping as winter approaches?)  The other radiators in the house don't seem to be a problem- they heat quietly and evenly.

- The pipes appear to be pitched correctly- the radiator steam source is a vertical pipe off the main, and the radiator return reaches the dry return in only about three feet and has a noticable downward slope.  The banging radiator is close to level.

-The steam is a Warren Webster system with a boiler return trap and a vent trap similar to those posted in the library section.  I don't think the boiler return trap actually does anything at the low pressures we run at, but the vent trap is the only vent in the system.  There are crossover thermostatic traps from the end of the steam mains to the dry return.  Everything appears to be original (pre-1940) except that there is a new gas boiler installed in the late 1990s.  The piping indicates that someone removed three radiators from the first floor at some point, but that doesn't seem to be a problem in keeping the house warm.

- I've replaced the insides of all the thermostatic traps (all radiators and the crossover traps), as it appeared from the way that they were painted over that trap maintenance had not been performed in some time.  That was quite a job to get them all open.  I used cage unit replacements. This didn't help.

- The pressuretrol is set to cut in at 0.5 psi with a differential (additive) of about 1.2.  There are no problems with boiler water level, and the wet return does not appear to be clogged.

- The steam mains are all insulated with fiberglass insulatiobn by the previous owner. 

This house is old but has been extremely well maintained, and based on the condition of the house I figure that this system has been working relatively well or work would have been done on it.   Other than the boiler and the missing radiators (which have been missing for a while) there is no sign that anyone messed with this system. 

Any suggestions are appreciated.


  • crash2009
    crash2009 Member Posts: 1,484

    Bump up to the front of the line
  • loud webster system

    doublecheck your pressure with a good gauge marked in ounces. it is possible that your pigtail has become plugged and is allowing the pressure to go over the limit for that trap, or is pushing a lot of water into that rad.--nbc
  • Jamie Hall
    Jamie Hall Member Posts: 22,900

    there is no horizontal run to that radiator -- which seems a bit unlikely, but is possible -- that eliminates the possibility of a water hammer on that feed line.  Which is the first thing I would have thought of.

    A question I would ask, though -- and don't take offence -- is it a real banging like a water hammer, or could it just possibly be expansion?  I have heard some astonishingly loud noises from radiators and pipes as they expand as steam gets to them!  Particularly if it is just a vertical line from the main that feeds this beast, something has to give somewhere as the riser -- and the radiator -- expand.  Can be the devil to find and fix...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • twopipe
    twopipe Member Posts: 16

    The pressure reading is at zero when this happens.  Its possible that my pressure gauge isn't working, but the noise happens at the beginning of the cycle when everything is cold and the steam hasn't yet reached the ends of the mains (it passes the riser for this radiator first).  So I think the pressure must be very low when this happens.  Later in the cycle, when the traps and vents have closed, the pressure should be higher but there is no noise at that point.
  • twopipe
    twopipe Member Posts: 16
    horizontal run

    Well, I took another look at that steam riser and there actually is a short (10") section of a horizontal pipe.  Looks level to me.   Another thing- the pipe from the floor up to the radiator valve is copper, not iron.  Could either of these cause the problem?

    As to the noise- good point.  All the radiators make some noise when they are heating- like a ticking or sometimes a pop.  This particular problem sounds like someone hitting the radiator with a pipe wrench every second or so.
  • Jamie Hall
    Jamie Hall Member Posts: 22,900
    Well now...

    I would check that 10" section of "level" pipe with a really good level -- and I'd want a good half inch to an inch drop on it over that length.  What diameter is it?  It's less critical if it's larger... but even so.  And what diameter is the copper riser?  If it's half inch or three quarter inch, while it itself won't hammer -- being vertical! -- you might get a good bit of condensate sort of bouncing around in it as the steam whizzes in (and condenses -- copper is a great heat conductor!) which then goes down to the horizontal and... bangs.

    It's a thought anyway.

    Have to admit the thing that really puzzles me at the moment is that the banging keeps going until the trap is shut.  More commonly, the banging will pretty well stop once the first section or two of the radiator is really hot...  that is, if it's a hammer problem in a feed line.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • jpf321
    jpf321 Member Posts: 1,568
    if you turn off....

    that "offending" big close rad .. does the banging disappear? what happens if you just turn the supply valve down a bit on that rad?

    cold big rads tend to bang because, as you suggest, they get steam early and produce a large amount of early cycle condensate .. that condesate rush can cause banging .. does the banging subside as the cycle progresses?

    also check on the other things people have noted .. but do try the easy test of what happens if you eliminate that rad from the equation or if you turn it down substantially. similar to "install a slower vent" and lessen the inrush of condensate flow.
    1-pipe Homeowner - Queens, NYC

    NEW: SlantFin Intrepid TR-30 + Tankless + Riello 40-F5 @ 0.85gph | OLD: Fitzgibbons 402 boiler + Beckett "SR" Oil Gun @ 1.75gph

    installed: 0-20oz/si gauge | vaporstat | hour-meter | gortons on all rads | 1pc G#2 + 1pc G#1 on each of 2 mains

    Connected EDR load: 371 sf venting load: 2.95cfm vent capacity: 4.62cfm
    my NEW system pics | my OLD system pics
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