One-pipe steam with two mains and water hammer

pvdsteam

This is our third winter in a house with a 1-pipe steam system. For the past two winters (and possibly the first) there has been a water-hammer problem in one part of the house. After reading many posts on this site and parts of the “Lost Art of Steam Heating”, I’ve learned a lot about steam systems and mine in particular. I’ve tried several things to fix the problem, but haven’t succeeded.



Here are the details. We have a Williamson OSB-4 boiler feeding radiators in a 3-story, ~2000sf house. There are two mains coming off the boiler. One parallel-flow main in the basement feeds mosts of the radiators in the house. A second counter-flow main feeds one radiator on the 2nd floor and one baseboard radiator on the 3rd floor.



The counter-flow main is the one with the water-hammer problem. The clanging starts immediately after the boiler cycles off on pressure, about 30 minutes after a cold-start. At this point, the radiators in the rest of the house are warm, but the two on the counter-flow main are cold. With the boiler off, I hear the sounds of a steam puff, followed by a loud clang, about a dozen times in the counter-flow main. This happens again when the boiler cycles off a few minutes later. After a few boiler cycles, the 2nd floor radiator in the counter-flow main gets warm, while the third-floor one stays cold. Note that after the first long boiler cycle (~30min), the boiler cycles approximately on/off approximately every 2 minutes until the thermostat is satisfied.



I attach pictures of the boiler. From reading a few other posts, the near boiler piping seems overly complicated, but I am not competent to judge.



A few things I have tried/fixed are:

1) I lowered the pressure in the system from a high of 5psi to a 3psi cut-out and 1psi cut-in. I can’t seem to go lower without breaking the pressuretrol.

2) I changed the main vent on the parallel-flow main from a Vent-Rite #77 to a Gorton #1. The main vent is roughly 50ft of 2in pipe.

3) I added a main vent (Gorton #1) on the counter-flow main on the 3rd floor immediately after the pipe leading to the radiator.

4) I insulated the near-boiler piping and main in the basement. (Not shown in attached picture).



These fixes have seemed to help somewhat, the water-hammer problem is still there. While I’ve enjoyed tinkering with the system, I’d like to get my weekends back. Any advice is greatly appreciated!

nicholas bonham-carter

Header size?

Is there a reduction in the pipe size of the boiler to riser, and then the header? I am having some problems with enlarging your pictures, so it's hard to tell. The main aim in piping the boiler is to slow down the steam in the header, and allow the water to drop down the equalizer to the return, and I'm not sure your piping is optimally configured for that. I think your boiler is a rebadged Weil-McClain, so you could go to the W-M website for the piping instructions.--NBC

Also, is the pressuretrol approved for horizontal mounting like that?

pvdsteam

Header reduction

Yes, you are right -- there is a reducer from 2.5" to 2" immediately out of the boiler. You can see this on the third picture. Sorry that all pictures were rotated 90 degrees when I uploaded. Could this be the source of the problem?



I think the pressuretrol is ok? It's mounted vertically.

SWEI

Looks like

the first part of that "U-header" slopes back toward the boiler as well.

Dave0176

Near boiler piping

Weil McLain's minimum piping should be 1) 2 1/2" riser and header, that is minimum. If there are two riser tapping out of the boiler id use both even if the manufacturer doesn't say so. At a minimum I'd use 1) 3" riser into a 3" header.



IMO you need to repipe the near boiler piping and your problems will go away, just go on the Williamson site and print the OSB manual.



Also the OSB 4 is DOE 144,000 BTU and 450 sq ft steam, that's a pretty big boiler, it needs big piping to get dry steam.

pvdsteam

Near-boiler piping

Thank you all for your replies!



I looked at the OSB manual and will find someone to repipe according to these specifications.



Two more questions:

(1) The output from the boiler is 2.5in, and my main is only 2in. Dave0176 suggested to use a 3" riser and header. But does this make sense if this will then be reduce to 2" immediately at the main? If so, what is the best way to pipe the size changes?

(2) As long as I'm repiping, it seems that I could also repipe the 2nd main (the counterflow that feeds two radiators) to instead tap of the single main. This would make the system be a single parallel-flow system, which seems much less complicated. Is there a reason not to do this?



Thanks for all your help!





I will try to find someone to redo the

Jamie Hall

The big header

is advantageous.  What happens is that the steam slows way down, and the water droplets drop out.  If the thing is pitched properly, the water travels along and down into the equalizer.  Meanwhile the steam -- traveling rather slowly (relatively speaking) gathers itself together and whooshes out the smaller riser.  So the thing to do is to go with the 3" riser and header, pitch it to the equalizer.  Equalizer connected by a 3" elbow, and you can reduce immediately to whatever on the vertical down pipe.  Then I would take the main off with a 3" T, and reduce that down to the 2".  You could use a 3x3x2 T, but the 3" with a reducer would work better.