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Steam Water Hammer Help!

dk1228dk1228 Posts: 7Member
Hello - I've been having constant water hammer/banging issues in my bedroom. My wife and I live in a NYC coop, constructed in the late 1970s. We have a two pipe steam system. We live on the 18th floor of a 30 floor building, ~400 units. We initially had loud water hammer around 6am when the building heating turned on, but following a wall excavation where they repitched a condensate return, we know experience water hammer noises every 1.5-2hrs, for 15-25 minute periods. It is driving us crazy as we are expecting a child very shortly and cannot get any restful sleep! I've attached a rough diagram of our heating set-up (heating unit is a in-the-wall PTAC Fridgedaire unit AC/steam heat).

In this diagram, "A" is the steam supply valve (which is always 'open', recently replaced), "B" is the Thermostatic Steam Trap (recently replaced), "C" is the vertical steam riser within the support wall, and "D" is the vertical condensate return pipe within the support wall. The condensate return pipe connects both to our heating unit as well as the heating unit from the apartment next door. I can confirm that the pitching in the heating unit (fin convection) is correct, as well as the pitching in the steam supply/condensate return to "C" and "D". We can control the heat manually, but we rarely if ever turn on as the steam riser is warm enough to keep the warm toasty (although insulated and within the wall). A few pictures to show the piping within the PTAC unit.

Unfortunately I dont have any pictures of the pipes within the walls leading to the riser/return pipes, but here are some additional facts.

1. When the steam is on: (i) the wall around the steam riser is warm to the touch, (ii) the pipes below "A" (steam supply valve) are hot to the touch and (iii) the condensate return pipe below "B" (steam trap) is warm. Dont know if this is normal (as living room unit pipes are all cold until we actually turn on heat). Also, could condensate form in the steam supply pipe below "A" when heat is not turned on?
2. The downstairs unit confirmed he rarely if ever turns on his heating unit, has heard loud banging when the heating system cycles on in the spring/fall, but generally does not hear any water hammer noise when heating is continuously on. He said he can hear some faint tapping, but not material enough to disrupt sleep.
3. The neighbor next door has told my building super that he has no issues with his heating unit, whether using his heat or heating or hearing any noise/banging.
4. When the banging begins, sounds varies from loud to soft to loud in no particular order, until it gets softer and softer and then silent (each cycle takes 15-25 minutes). When I touch the condensate return pipe under "B" (steam trap) during the banging, I can feel the vibration through that pipe. There is a faint vibration under "A" (steam supply valve) but noticeably less than under "B". I can also feel the wall vibrate near the main vertical condensate return pipe when I place my palm on it.

This has been driving me crazy and my building management is 'trying' to help but they dont have to deal with this every night. I've been told that the expansion joints in my building unit 'line' have been replaced. Can anyone help think through possible fixes -- we have a steam heat 'specialist' coming in early next week to take a look but I am skeptical of what that means (I fear his visit will coincide with the period between banging noise). Any help would be much appreciated!


  • the_donutthe_donut Posts: 374Member
    Lots of units involved, lots of variables. Might have a failed trap Next to you and steam is smashing into water. What caused the neighbors to work on the pipes? Sounds like issue got worse when that happened.
  • dk1228dk1228 Posts: 7Member
    I asked building management to take a look at the pipes within our bedroom wall due to the loud banging at 6am when the heat turned on in the spring/fall. They opened the walls, immediately noticed the condensate return pipe went down and then up so replaced the pipe to be straight (and pitched down into the main return). Now kinda regretting it :(
  • Jamie HallJamie Hall Posts: 12,102Member
    You appear to have two valves on the supply -- the manual valve, and then above it an electrically closed valve. That second valve is, I presume, connected to a thermostat or some such gadget? The comment that the pipe below the valve gets hot -- unlike the living room pipe -- and the return pipe is warm -- also unlike the living room pipe -- makes me wonder if one of those valves is letting steam by when it shouldn't. In fact, it is possible that if the motorized valve is letting some steam by, it occurs to me that one possibility is that condensate is being slammed against it as the steam is coming in.

    So... one question might be, do you get the banging when that valve is open, or only when it is supposed to be shut?
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • the_donutthe_donut Posts: 374Member
    That may have been a water seal.
  • dk1228dk1228 Posts: 7Member
    Banging occurs both when the electrical valve is open (heat button is turned on) and when supposed to be closed. The fin convectors are not hot when the heat button is turned off. I've tried turning the heat on (fins are warm and fan is blowing hot air), and can still hear banging in pipes/through the wall.
  • dk1228dk1228 Posts: 7Member
    Some additional pictures of the steam riser and condensate return pipes if helpful...

  • the_donutthe_donut Posts: 374Member
    How far down did the old condensate pipe go up and down? I am wondering if they piped it this way to seal condensate from steam. Traps looks new. Maybe system had orifice and water seal.
  • dk1228dk1228 Posts: 7Member
    Drop wasnt that noticeable - wide v, maybe an inch or two. Honestly it looked like it was a space saving move more than done intentionally but who knows. I noticed the vertical condensate pipe is quite warm as well - is that normal? I also couldnt tell whether the steam supply riser or condensate return was the source of vibration (tried holding on but both were too hot). Would some sort of fiberglass batting all around for noise reduction help or is that just a bandaid. Trying to think thru all possible options if building decides to stop being helpful.
  • the_donutthe_donut Posts: 374Member
    There's warm and then there's steam hot. I am going with failed traps somewhere on that return. Steam is filling return and slamming into condensate. Before you had enough of an up and down that the wave didn't have enough distance to hammer as bad. Now you have a drag racing line where waves can build and slam much harder.

    Building needs to fix failed traps. Failed traps will cause other traps to fail, rooms to overheat and other rooms to not heat. They will turn up pressure to heat rooms and damage TRV's and overheat more apartments.
  • dk1228dk1228 Posts: 7Member
    I am assuming the circular devices on steam supply and main condensate return pipe are orifice steam traps. Those were definitely not there before. Could those be causing the water hammer?
  • the_donutthe_donut Posts: 374Member
    Those are pipe flanges for joining two sections of pipe. Pretty sure issue is on condensate side. Sometimes steam zone valves can cause hammer too, not allowing condensate to drain until valve opens. A vacuum breaker is used to let water drain, but I am leaning towards steam in dry return from failed trap. You could have them install a vacuum breaker on condensate line.
  • dk1228dk1228 Posts: 7Member
    Thanks. The condensate return pipe is definitely hot, not just warm. Probably from steam thru a failed steam trap. Could they just install a vacuum breaker on the main vertical condensate return pipe, or only before the thermostatic steam trap in the heating unit?
  • the_donutthe_donut Posts: 374Member
    The vacuum breaker would allow condensate trapped by the vacuum and closing of zone valve to drain when the trap is full. Should be installed between the trap and radiator. Failed traps need to be replaced.

    A good steam guy needs to look at whole system and get all the parts working together.
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