Water hammer when boiler is cycling

Cloversm

We live in an old 4 story 8 unit condo building that I have become the defacto maintenance person for. We have a one-pipe steam system, a Weil McClain boiler (installed in 2015), a McDonnell Miller series 47 water feeder/low water cut-off, building water pressure is about 80psi. The issue is that something seems to cause a loud water hammer in the domestic water pipes at random times for random lengths, but only when the boiler is cycling and it never happens in the non heating season. It used to happen only once a week or so (but has always happened for the one year that we have been here), but is now happening with almost every heating cycle. There is a check valve on the makeup water line that should be stopping any backflow as well. I read something similar on another discussion on this forum, and the recommendation was to install a pressure regulating valve on the makeup water line but our plumbers dont seem to think that is the solution.

Our plumbers are perplexed. They are convinced that it isn't being caused by the poppet valve on the water feeder because it operates fine and without the hammer when doing a blow down of the system. And therefore dont think that the pressure regulating valve is the solution. They are looking at other potential issues in the building as a whole (including the pressure reducing valve on the main water line), but this hammer issue only happens when the boiler is cycling. I've attached photos of the boiler and the water feeder assembly. Are there any other potential causes for this hammer in the water lines to happen only when the boiler is cycling, only at random times for random durations? Any help would be greatly appreciated. Im worried that if we don't find the solution soon, the vibration is going to cause other leaks in water piping somewhere.

ethicalpaul

They are saying the hammer is in the water lines and not in the steam lines?

Jamie Hall

You say you have a pressure reducing valve on the main water line? Do you also have an expansion tank for the domestic hot water? If not, you need one. That may not be the water hammer problem, but whether it is or not you need to have it anyway.

Another question comes to mind. Do you any idea how often your automatic water feeder is adding water? It shouldn't be adding more than a gallon or two per week. If it's adding on every cycle of the boiler, or even every third or fourth, you are adding too much water -- and that means you have a leak somewhere, which you need to find and fix as soon as you can, before the fresh water wrecks the boiler (unless, of course, the leak is in the boiler itself, in which case... oh dear).

All that said, the most likely villain is a quick closing valve somewhere -- like maybe the check valve on the boiler feed line.

What pressure are you running the boiler at? It shouldn't be more than 2 psi, and at that pressure the check valve shouldn't hammer. But...

neilc

what pressure are you running at?
that one picture of the gage looks like it's up a bit,
better picture of the gage and pressure controls please,
pressure should be low, low, under 2#.

That header is only coming out of the one side?
boiler that size should be using both sides.
The long main coming at us, it doesn't have any sags at all, does it?
and is it pitched back to the header, or away to a trap or drop to wet return?
picture of that end??
All that steam pipe could use insulation.

EBEBRATT-Ed

That's not a McDonnell Miller 47 it's a #51 not that that matters. I agree with the prv and expansion tank comments above. Take the check valve out and put a backflow preventer in it's place.

Cloversm

@ethicalpaul yes, hammering is in water lines, not steam pipes.
@Jamie Hall there is a regulator on the main water line and we’ve had no issues with it. Hammering is only associated with boiler operations it seems. And we do have a expansion tank on the domestic water line at the boiler for the hot water. I don’t have any idea how much water is being made up. There doesn’t appear to be a leak at the boiler or anywhere in the basement. We did a full review of everyone’s rads in the middle of Oct when the heating season really started here (western PA), and there were no apparent leaks in the units (replaced a few noisy vents but that’s it). We have replaced both main line vents in the past year and the plumbers did a full boiler maintenance/service at the end of September before the heating season with no major issues presenting themselves.
@neilc looks I be about 1ish. I’m not sure of hg vs psi. I think that everything is pitched correctly and the header does appear to only be coming out one side.

I didn’t know anything about steam anything until about a yr ago so this is all stuff that I’ve learned out of need. I’ve attached a few more photos in hopes that they help.

neilc

so that gage is showing vacuum @ 1,
do you ever see it above the zero?
are we sure its pigtail is clear?
or the others?
what's all that looping pipe at the other end of the main?
can we see one more without that bright light, maybe from the other side?

Jamie Hall

While there are some things about the heating piping and boiler which are not, perhaps, quite as they should be, it is important to remember: if the banging is in the water pipes, not in the steam system, even though it is associated with the boiler running it is a water problem, not a steam problem.

Which brings me to... it is rare to have water hammer in a water system unless somewhere there is a valve which is closing quickly. Which leads me back to that check valve and the automatic water feeder.

If the banging is fairly consistent -- that is you can be reasonably sure that it happens on pretty much every boiler run -- the simplest thing to do is to valve off the automatic feeder completely for a few runs and see if you still get the banging (do keep an eye on the boiler water level, just in case part of the problem is serious leakage and the feeder is opening and closing). Granted, you are then trying to prove a negative, which is almost impossible to get right, but it's worth a shot. That will also tell you (since you are watching the boiler water level) if you have to feed water...

neilc

and in that same "Main" picture, is that header pitching up as it leaves the boiler?

Cloversm

The plumbers will install and prv on the makeup water line tomorrow and double check that the check valve is operating properly to see if that fixes the issue.

Cloversm

Installed a B&G B38 prv on the makeup water line and made sure the check valve is operating correctly. We have been hammer free for more than 24hrs, so I think that we found the fix. Thanks for all your help!