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Water hammer in dry return...

Rory Member Posts: 7
This is my first real heating season in our new (old) house. I have a two pipe dry return system. The system had a pipe plug in the main vent location, and steam distribution was abysmal. The burner would short cycle and steam would travel back through a section of pipe connecting the main to the return in order to push air out the return vent. It had been running this way for at least ten years and the fuel bills were astronomical. I've since put a Hoffman 4a at the end of the main to match the one on the return. The main now fills in minutes! Every rad gets hot all the way across, even the third floor which never had heat before! However, I've now created a new problem. The horizontal run connecting the end of main to the return hammered some before, but now that I'm ACTUALLY making condensate it hammers like crazy. My question is this: Can I simply lower this connection below the water line? My fear is that it may affect tit's ability to put water back into the boiler if I do. I think a setup like this would normally have a F&T on the main drip but I'm looking for a quick short term solution at present. My near boiler piping is up against a wall and difficult to photograph, so here's a diagram of what I'm working with. Thanks in advance to anyone who just read my novella...


  • 4Barrel
    4Barrel Member Posts: 125
    couple thoughts

    - test the hoffman 4A on the return. is it venting at the start of a cycle?

    - is the dry return where you get the hammer properly pitched back towards the boiler?

    - if these two items are not issues, perhaps the vertical segment of the return is not a properly sized, such that condensate fills it and backs up into the horizontal portion. this might be complected y the check valve if also is not operating properly

    i'm not sure if changing the location of where the dry return drops into the loop would make a difference. but i'm not a pro, and perhaps one can comment on any inherent flaws in the design of your return/loop system. 

    i have dry returns, but a simpler design, where both dry returns (in attached pic they are in the background, equalizer in the foreground) drop vertically and thereby become wet. they then link together form the bottom of the loop. no check valve.

    hope this helps.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    edited October 2012
    dropping returns

    those returns should only connect well below the waterline [floor level]. the flapper in the check valve should be removed, and i think all will be better.

    the most popular main vents are the hoffman 75 [pricey], and the gorton #2 [capacious]. the 4 a may not be right for this application.

    probably, pressure was driving the water out of the boiler up into the returns,and that was the reason for the check valve. keep your pressure low, and you won't need it.

    just checked, and the gorton #2 has 10x the venting cxapacity! you can never have too much venting!--nbc
  • Dave in QCA
    Dave in QCA Member Posts: 1,785
    Yes, Lower it

    Yes, you can lower the point where the return connects and you should lower it.  It will never work correctly the way it is piped.  The return piping shoud ideally tie in at the very bottom of the piping at the same level where the drip from the steam main connects. 

    The piping shown in 4barrel's photo is ideal.  Make yours look like that.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • Rory
    Rory Member Posts: 7
    Why a checkvalve?

    Yeah, I'm not sure about the check valve either... The previous owner had been running this setup at 5psi. I've got it down to .5 cut in 1.5 cut out, which I think is getting close to the least amount the pressuretrol will operate. Maybe try a vaporstat in the future. The 4a's may be bottlenecking my venting, but are working fine for the time being. I'm going to see if I can lower that section of the return today, thanks for the replies.
  • Rod
    Rod Posts: 2,067
    2 Pipe Steam

    Hi Rory-

       Others have already answered your questions. I’ll just add a few comments and drawings that may be of help to you.

    -On a two pipe system you can deal with the main in two ways, either with a cross over trap (No main vent on the steam main) or like a drip to the wet return from the end of the steam main. (Main Vent needed on the steam main)

    -The Hoffman 4A s are pretty small I’d increase the size of your vents. The Gorton #1 has 3 times more venting.  The Gorton #2 has 8 times more venting.

    -The one way valve needs to be removed as it has No purpose.

    -The return pipe coming up from floor to the equalizer needs to use an elbow and a close nipple at the connection to the equalizer. Using a long nipple can result in water hammer.

    - Near Boiler Piping- If the piping is configured like it is in your drawing it needs to be changed as this is producing wet steam.

    You’re very lucky that you have a two pipe system as they can really be tuned up. Since they can run a very lower pressure you will probably need a Vaporstat for low pressure control and a low pressure gauge. This gauge is in addition to the required 0-30 PSI gauge you already have. Running at a lower pressure saves fuel.

    You might also want to look into orifices. Use the “Search the Wall” function and check Dave in QCA s past posts as he has done a lot with orifices.

    Once you get your system straightened out, it should purr and give you comfortable and economical heating.

    - Rod
  • Rory
    Rory Member Posts: 7
    Thanks everyone.

    Thanks, Rod. I'm afraid my drawing may not be to scale, there is actually about 36" from the water line to the header so I think I'm alright on that one. I'm glad the general consensus agrees with my theory, I'd like to know who installed this system. If the 4a is small, it still does the job 100 times better than a pipe plug! Definitely look at increasing my venting capacity in the future though.
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