1 pipe system 2 rads expanding - making noise.

ksd99

Hi all
I have 2 radiators (identical) that make this noise at the beginning when steam us going into the radiator. I’ve picked them at both ends etc ;.....cannot get rid of the noise. A very reliable steam person told me it sounded like expansion vs hammering ....and I should tighten the tension rods a bit - my rads don’t have them 😞 Any suggestions. The noise drives me crazy.

youtu.be/Z6ypcnOfiTg

Jamie Hall

Have you tried putting something slippery -- like pieces cut from a plastic milk jug -- under the feet? Sometimes that can help...

Hap_Hazzard

That sounds like water hammer in the runout to that radiator. The radiator is just acting as a transducer because it's at the end of the line, so it turns the mechanical energy into sound. Can you access the piping from the basement? Try putting your hand on the pipe (use a folded rag or pot-holder) and see if you feel the impact. Then check that pipe with a level and see if it's pitched correctly. It should rise at least 1" per 20 ' towards the radiator.

The thing about expansion noise, aside from being quieter, is that it's followed by contraction noise when the radiator cools down. A radiator can't keep expanding indefinitely, right?

ethicalpaul

I have one radiator doing this and I felt it was metal expansion. But now I think there is in fact a place where water collects in its runout (to agree with @Hap_Hazzard above), probably just a little that causes these little pinging hammers.

ksd99

Hap_hazzard-There was no impact to the pipe in the basement.
ethicalpaul - how do u deal with the noise - I cannot stand it
Jamie - i tried the milk jugs - no difference.

I tried pitching the rad more then I should and I still get the noise. Maybe it’s a flaw in the design because as I mentioned I have 2 rads that do the same thing - only at the beginning.

Any other suggestions - the room they both are in is A room I often like to use, except when the boiler is on 😣

nde

Sounds like slight water in sagging runout as others suggest. I fixed one rad with similar issues by putting 2 quarters under each leg at vent end and one quarter under each leg at runout end. You can test first by raising the pipe end first (may have to experiment with a wooden wedge on how high to raise) and then adjust vent side so it is slightly higher. I have expansion noises that are much louder, more like a crack on both heat and cool, I have fixed some of those by slipping metal dog tags under rad feet to let them slide a bit. In the end expansion noise and/or sag pings are just part of an older steam system.

ethicalpaul

Mine is not too bad. It's a pretty gentle "tink" or "ping", I get maybe a dozen of them a few seconds apart during the start of a heat cycle.

Here is my situation, see if you might have a similar one.

The green arrow points straight up to my radiator. This takeoff is not typical. It's a straight 90 degree turn off a spur off the main.

The main is the insulated pipe to the right. It comes to this tee and turns toward the camera to feed the rest of the house.

The tee that you can see is maybe 6 feet downstream of the high point of the main, about 6 feet to the right (this is the first radiator that gets fed from the main).

But if you think about it (or if you carefully measure it), if the high point is to the right, that means that the part of the runout pointed to by the red arrows must be sloping down. And water is lying there ALL THE TIME.

At the start of the cycle, that water is cold (I could minimize the hammering by insulating it I suppose, but I’m going to re-run it this summer when I install my new boiler anyway).

The steam hits that cold water and condenses very quickly forming a vacuum which apparently picks up the water and slams it somewhere. As the heating cycle warms everything up, it becomes hot water lying there, almost at steam temperature. So the steam stops collapsing upon hitting it, and the pinging stops.

Hap_Hazzard

@ethicalpaul, I think you're confusing the two types of steam hammer. Thermal shock is what happens when steam encounters a pool of cool water and collapses, causing a vacuum. When steam flowing over liquid water causes turbulence and creates water pistons that slam into the end of a pipe, it's called differential shock. This video illustrates both types of steam hammer.

ethicalpaul

I was just stating that I hear pinging and that I think it’s caused by steam collapsing after coming into contact with cool pooled water. I didn’t name either of those terms. I don’t feel confused.

BobC

@Hap_Hazzard That's a great video -thanks.

Bob

Hap_Hazzard

ethicalpaul said:

I was just stating that I hear pinging and that I think it’s caused by steam collapsing after coming into contact with cool pooled water. I didn’t name either of those terms. I don’t feel confused.

What you were describing sounded like thermal shock, but you said it "apparently picks up the water and slams it somewhere," which is typical of differential shock. If steam collapses due to cold water lying in steam pipes, it would draw air in through the vents, which are still open while the system is starting up. There isn't enough water available yet to do any slamming.

ethicalpaul

As I wrote in my post, there is always water lying in a low spot in a pipe. It's definitely not what you are calling differential shock. The steam isn't moving that fast and the pipe is too big and short.

It's steam condensing from hitting the cool water lying in the pipe is my theory. Are you saying I'm wrong? I'm asking honestly because I'm not sure what you're saying.

Surely you would agree that with "thermal shock" the water does get picked up and thrown?

Jamie Hall

The steam collapsing type of situation usually will give more of a panting sound in a one pipe system -- and may be quite inaudible in a two pipe system where the vent is far away or the puddle is on a runout. It will also effectively stop the steam from going by until it is very hot -- so a slow radiator may be caused by it. True water hammer, though, which is aptly named, happens when the water -- which is likely to be a puddle when it's sitting still -- gets picked up by advancing steam and slammed against an obstacle, such as an elbow or a T. Usually a little later -- steam has already gotten past the puddle and heated the pipe, so it is moving rapidly (and the puddle may be from condensate unable to drain back fast enough). It doesn't slow the heat to the radiator much.

Both have the same fundamental problem, though -- a piece of pipe with inadequate pitch.

Hap_Hazzard

ethicalpaul said:

As I wrote in my post, there is always water lying in a low spot in a pipe. It's definitely not what you are calling differential shock. The steam isn't moving that fast and the pipe is too big and short.

It's steam condensing from hitting the cool water lying in the pipe is my theory. Are you saying I'm wrong? I'm asking honestly because I'm not sure what you're saying.

Surely you would agree that with "thermal shock" the water does get picked up and thrown?

No, in a steam pipe it really doesn't. In the demo, yes, the water slams into the bottle, because they stick a bottle full of steam into a pot or bowl full of water, but in a steam pipe you're dealing with a relatively small puddle of water and a lot of air available to fill the vacuum. Since it occurs at startup, as the steam front reaches the pooled water, there's still a lot of air up ahead that gets pulled back when the steam contracts, and additional air can enter through the vents. This is what causes the "panting" noises people often talk about. It might occasionally cause a ping, but not the kind of banging you can get from differential shock.

ethicalpaul

OK I can't prove you wrong. But something is making these repeated clanks. I might learn something when I do cut that pipe.

But we can agree as @Jamie Hall said, that either way, if we're talking about hammer it's due to water hanging around in the pipe where it shouldn't be?

Hap_Hazzard

ethicalpaul said:

OK I can't prove you wrong. But something is making these repeated clanks. I might learn something when I do cut that pipe.

But we can agree as @Jamie Hall said, that either way, if we're talking about hammer it's due to water hanging around in the pipe where it shouldn't be?

Not necessarily hanging around. Like Jamie says, it can happen when the condensate just isn't draining fast enough.

Differential shock is most likely to occur when the depth of the running condensate and the steam velocity are at their maxima. That's why it always happens when the system is being pushed to its limit, coming back from a setback, or just running a long cycle on a cold day. A runout that has marginal pitch or diameter can sustain a short cycle where the steam velocity starts slowing down before the condensate gets really deep, but when the radiator is really working, sucking steam and producing condensate as fast as it can, the steam kicks up waves in the condensate that grow high enough to reach the top of the pipe and form water pistons that get pushed to the end of the pipe by the full force of the steam, picking up more condensate as they go, until they slam into the elbow.