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Steam Riser Banging Like Hell (and a little history)

justinh Member Posts: 7
I am the condo board president at a 16 story historic lower Manhattan building. The building was built in the 1920s and abandoned for a long time. Developers acquired the building in the 80s and did a complete renovation to convert into condos. Our heat is a two pipe steam system run on a Federal FST 200 boiler currently running on gas. In an effort to update, upgrade and improve efficiency, a few years ago we had our boiler company install new controls, a new burner (Industrial Combustion DLG-84P). They also reconfigured our near boiler piping. Heres why: According to our engineer/consultant, in the 80s conversion, the engineer who designed the system converted it to a high pressure system by reducing the 10" steam outlets to 3 and 4 inch and connected those to the 12" main header, and ran the system at 8-10 psi. (There was also no Hartford Loop!) Banging used to be the norm in that old configuration. Since opening up the outlets again to 10" and replacing all 200plus radiator steam traps and all F&T traps in the boiler room, we've been able to run our system way more efficiently at 1psi. A bit of knocking is still an issue at some radiators but in general we're happy with the quality of the heat. HOWEVER, since opening that outlet back up to a normal 10" diameter, there is one riser that is experiencing hammer from hell. Even all new traps has not helped it improve. I am almost 100% sure that the riser in question is an express riser to the top of the building that leads to our roof tank room which provides heat via 2 fin tube radiators to our standpipe system water tank to prevent freezing. From the tank room it does branch off to one neighboring radiator in the penthouse. The return runs right along side the riser. No other risers bang like this, even a riser that shares a header with the banging one. I've noticed that the lower the pressure we run, the less intense the banging, and have thought about running as low as .5psi. Also, to be expected, the more frequently heat is called for, the less intense and prolonged the banging since the pipe isn't cooling off as much. But it still bangs some every cycle. I would like to hear anyone's thoughts on why this one riser (likely an express) might be banging so violently. And it is violent! And very disruptive to residents adjacent that riser - especially in the fall and spring and especially in the morning when the system hasn't called for heat through the night. Obviously there is moisture in there. But shouldn't it be dripping down and draining through the drip line? It is vertical after all (and the header is pitched properly.) Could really use some advice or insight! Thanks very much in advance for all your collective brain power!


  • Is the pipe running completely vertical, or could there be a horizontal somewhere which is now pitched badly?
    Post some pictures of the boiler piping, and the F&T traps.--NBC
  • Jamie Hall
    Jamie Hall Member Posts: 22,952
    There almost has to be a horizontal in there somewhere -- possibly quite short. Is the drip at the bottom directly under the vertical? I can imagine that even a short offset on that might bang like crazy.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 11,021
    The only express riser to the attic I have worked on (very small potatoes compared to yours) had dirt legs at the bottom then going into a F&T.
    The dirt legs were so full of sludge that they would barely drain into the F&T. (1932 install)
    Every supply drop also had dirt legs before traps.
    They also were full of sludge.

    Or you have a horizontal section(s) that has settled from the weight of the pipe. (as mentioned above)
    That has to be a tall and very heavy pipe.....what size is it?
    Any prints of piping, might show offsets and supports.
  • justinh
    justinh Member Posts: 7
    Thanks for the thoughts so far. Here is a rough diagram of the piping in the room just off the boiler room where the noisy riser shoots up. And some pics. There is a lot of horizontal before it gets to the drip/y strainer. But there is no audible banging in this room - other than what you can hear from the 2nd thru 4th floors where the banging is most intense. I can see an offset on the riser around the ground floor and assume there are others. Unfortunately its so difficult and disruptive to open walls in residents apartments to take a look at the pipes in the chase. Maybe a heat camera can give me an idea about any horizontals that may be back there? Also, I have no idea why that big gate valve is on the header. Wonder if that's holding water. Is it possible that water trapped in the header in the basement level pipes (horizontals) could be leading to hammer on the floors above? Or would it only be banging where the water is sitting?
  • Fred
    Fred Member Posts: 8,542
    edited November 2019
    Does that riser just service the 2nd through the 7th floor? The riser is there because there are horizontal radiator run-outs off of it to various radiators. It is possible that riser has settled (dropped) a little, enough to cause the horizontals tied to it to lose its pitch and those horizontals are holding condensate.
  • justinh
    justinh Member Posts: 7
    Fred, I am almost positive that the riser is an express up to the roof tank room where our water tank is. I have only found radiators in that tank room and one other adjacent room next to the tank room that branch off the riser - basically at the 17th floor. Those radiators are adequately pitched. In all other apartments on the way up to the top, it runs in a chase behind walls with no fixtures branching off. Banging is loudest on floors 2, 3, 4 behind the walls. But the riser doesn't service those floors.

    JUGHNE, unfortunately there are no existing prints of as-built piping from the time installation in the 80's. At some shady point in time all docs that were filed went missing from the NYC DOB. Lot's of dubious history with the developers.
  • justinh
    justinh Member Posts: 7
    Attachments in earlier post were not viewable. Here are some visuals of the piping and a rough diagram.

    Rough Diagram

    Large insulated pipe is the header. Beyond the hole in the wall is the riser.

    4" gate valve on header. Not sure why it's there.

    View of gate valve and header

    F&T Trap and y strainer
  • JohnNY
    JohnNY Member Posts: 3,226
    @justinh, If you think I can help you, let me know.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,492
    You need a trapped drip pipe at the base of the express riser. Leave some vertical space (as much as possible) between the new tee connection to the riser and the inlet to the trap so the falling start-up condensate can quickly get out of the steam's way. That should solve the water hammer.
    Retired and loving it.
  • If you can open the upper end of the pipe, you could stick a wire cable, or measuring tape down to see if there is an offset in the riser, and at what height. In the meantime, can you arrange some other means of heating the tank, and cap off the riser?—NBC
  • retiredguy
    retiredguy Member Posts: 888
    edited November 2019
    If you can open the upper end of the pipe, you could stick a wire cable, or measuring tape down to see if there is an offset in the riser, and at what height. In the meantime, can you arrange some other means of heating the tank, and cap off the riser?—NBC ------------------------- In addition to this I would ask plumbers if they had a snake with a camera that they could send down the pipe for a visual inspection.
  • troubleshoot
    troubleshoot Member Posts: 1
    The riser is pressurizing to quickly throttle down the riser valve so steam travels and heats slower. What type of vent set up is in the roof tank? Sometime steam traps mixed with venting can cause vapor lock holding condensate water from flowing