Arco Water Hammer

WestchesterGuy

I think I have an Arco vapor system. I have one radiator above the garage with water hammer. I tried elevating it a bit, but no luck. Any ideas? Thanks.

BobC

Check any horizontal pipe that runs to that radiator to make sure it slopes back towards the radiator.

Bob

Jamie Hall

BobC said:

Check any horizontal pipe that runs to that radiator to make sure it slopes back towards the radiator.

Bob

Back towards the radiator, @BobC ? I know what you mean, but it's not as clear as it might be. Any horizontal run on either pipe -- boththe feed and the return -- must slope so that the end nearer the radiator is higher than the end where it goes into the main or the return. Sometimes raising the radiator slightly will accomplish this -- but not always. One really has to get under there and trace all the pipes and check each one. Also, if any of them are long, check for sags.

BobC

I screwed up; I meant to say back towards the BOILER. If the pipes don't allow water to drain back to the boiler they can pool water and that can cause water hammer.

Bob

WestchesterGuy

Thanks, guys. I put those blocks under the legs (you can see in the picture) in the spring and it didn't seem to help. I guess I'll have to open up the ceiling below and have a look at the pitch. This is the only part of the system above the garage that isn't exposed unfortunately. Have you ever heard of the hexed nuts on the supply valves needing adjustment? Or maybe the orifices on the valve failing and causing water hammer?

Jamie Hall

Anything's possible with steam... anything. But -- no, it's unlikely that it's a problem with the valve or the orifices.

Valves partly open or failed on one pipe steam can cause all sorts of noises -- but not on two pipe, and particularly not on a vapour system.

Fred

Is the hammer actually in the radiator? If so, there is the possibility that crud has built up towards the drain end of that radiator making it slow to drain out. Might be worth disconnecting that elbow and checking that before cutting into the ceiling. Of course, If the hammer is coming from under the floor, then it is most likely a horizontal pipe between the floor and the ceiling.

WestchesterGuy

Very helpful, much appreciated. You can kinda feel the hammer on the supply line. Not really in the radiator. But it's definitely a lot easier to look at that elbow before opening up the ceiling below anyway.

BobC

Here is a primer Dan did a while back on water hammer in steam systems -

https://heatinghelp.com/systems-help-center/water-hammer-in-steam-heating-systems/

Bob

JUGHNE

If the orifice in the valve was out of whack and If you throttle the hand valve almost closed to limit the steam flow and then the hammer stops, perhaps it would be the orifice being the issue.

Does the rad heat all the way across to the outlet elbow?

Danny Scully

That's a model k system. The orifice is in the hand valve and is adjustable, although, that might get tricky. The orifice is suppose to be adjusted to match the condensing ability of the radiator. It's possible it's set wrong and allowing steam to pass into the return, which may be the source of water hammer.

WestchesterGuy

I will check to see if the rad heats all the way, I hadn't checked for that before. And I will separately try closing the valve.

JUGHNE

With any orifice system the size or adjustment of opening is dependent upon the pressure applied.
Is it possible you are running higher pressure than usual?
I would check that first before opening anything up.
Your pigtail could be partially plugged.......vaporstat out of adjustment. You should have a 1-3 PSI gauge for control checking.

Excessive pressure could be pushing more steam thru that orifice valve and getting to the water in the returns.

WestchesterGuy

Here's an update: the hammer occurs at the beginning of the cycle. It is in the steam pipe, not in the radiator itself. The radiator then heats up completely, all the way across. One other piece of info, not see if it is relevant: by the boiler, there used to be a single trap at the end of the return. It was replaced with a steam vent. Maybe it's possible steam is coming up the return from the boiler and I need to get a real trap back on there? Any ideas would be greatly appreciated. Thanks again.

Jamie Hall

A trap at the end of the return? All the returns should drop down to a wet return. If they do -- and the pressure is OK (particularly at the beginning of the cycle when there is no pressure) steam can't get into them.

However... I presume this return is a dry return, and was always a dry return. Any chance at all that it was once a wet return and the boiler water level got changed? That can cause all kinds of havoc...

On water hammer at the beginning or very near the beginning of a cycle, however. That is almost always -- not always, there are exceptions -- to be found to be caused by a near horizontal runout which is sloped the wrong way, or a sag in a longer runout. Doesn't take much. Check every inch of that runout.