water hammer

David Lampe

Here is my series of questions.
I have a two pipe vapor steam system similar to the types described in Lost Art and "We Got Steam Heat". On page 53 in "We Got Steam Heat" is a drawing of the type of vapor steam trap we had on the radiators (a dip tube with a ball check valve).
I have replaced all the check valves with modern Hoffman thermostatic steam traps since about half the original traps had no ball check so steam was entering the returns, and causing havoc with the radiators upstairs, some never got heat. This problem is fixed. They have so much heat upstairs I am able to lower the thermostat down to 66 degree Fahrenheit I have a small two family house about 1600 square feet, my gas fired boiler is a Burnham it does not have a "wet" return on the floor or under it in
the cellar floor. The steam mains are piped along the supporting beam of the center of the house. At each end is a riser to the upper floor and two risers in the middle of the house like a the "plus" sign with the boiler in the middle.
The returns are simply piped parallel to the steam mains and insulated with asbestos the "header" or supply pipes are 2" diameter. The long connections outward to the radiators are 1" the connection at the floor are 1/2" up to
the radiator the returns lines are 1/2" down to the floor line then change to 3/4". As all the returns get close to the boiler they attach to a 1 1/2 or 2" return pipe. The return pipe is right next to the boiler. I measured the static height it is 40 inches, the "A" dimension, from the lowest steam pipe to the water line of the boiler.
I didn't see any F&T traps on the ends of the mains.
I also checked the Hartford loop to see if it was put together properly. The loop is ok and seems to have a water seal. The boiler is on a pedestal of concrete about 4 inches off the floor of the basement, so it is likely the second or third boiler used in this old house ~ approx 85 years young. I don't have any idea what could be below the
slab, I'm not sure I want to know.

The returns are all covered in asbestos insulation except inside the 1st floor apartment the risers and returns were not insulated I have recently re-insulated these 1" inch steam riser supply pipes with fiberglass. The pressure on the pressuretrol is set under one pound, the boilers max
doe rating is 144,000 btu
My main vent is now spitting a lot of water and the system which had no water hammer before now has water hammer on startup for one minute or so on the return lines near the boiler.
I checked the drawings from the book we got steam heat this morning the Hartford loop appears to be correct and I will try to clean the main vent in boiling vinegar to see if it is simply stuck or dirty. I will replace it if needed.
The glass gauge recently got some extra rust particles. It was very clean until I added the new traps. The gauge waterline goes about halfway down on startup and it needs water about once per week during heating season.
What can I do to resolve the water hammer problem ?
What can be done to make sure the main air vent is properly sized? I currently have a Gorton vent number #1 and it is spitting water and may need to be replaced.

Dave Meers

water hammer

Hi David,

I think you are confusing "A" & "B" dimensions. Your two pipe is ruled by a "B" dimension, measured from the end of the dry return ( where you Gorton #1 is located ) to the waterline of the boiler. Compare that dimension to the operating pressure of your boiler. You need at least 28" of "B" dimension for every one pound of steam pressure. Since your main air vent is spitting, I suspect the pressure is rising above what your "B" dimension can handle, thereby stacking water up in your dry return and trying to get out through the Gorton #1. You said the pressuretrol is set at one pound. You probably want to use a vaporstat and operate at below one pound. The steam traps can take the pressure, but it sounds like your "B" dimension can't.

Your water hammer will not be in the dry return unless steam is getting through one of the new traps. Check each radiator to make sure the traps are working. Did the hammer just start after the addition of the traps? Are you sure it is coming from the return lines? Does it go away after the one minute? I'm going to have to think about this, please give me some more info.

Best regards, Pat