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!