Could Bad Main Return Vents Cause Water Hammer?

Dairon421

Hey guys we installed a new boiler and the near boiler is correct, all the radiators valves are open and the main is pitch correctly. The boiler was still knocking . I changed 1/3 main return vents and was still knocking. Came back today and the other 2 main return Vents that was hidden . Changed them both and boiler stopped knocking.... Can someone please explain why changing the main return vent will cause water hammer 

ethicalpaul

The pressure might have risen to a point that could cause water level problems.

did you skim it?

can we see the correct near boiler piping? It’s such a rare treat.

pedmec

The vent might not have opened back up after the pressure dropped and formed a vacuum. this could have cause flashing of the condensate because its at its saturation point already. flashing of the condensate and rapid contraction of the steam is one cause of water hammer.

ChrisJ

pedmec said:

The vent might not have opened back up after the pressure dropped and formed a vacuum. this could have cause flashing of the condensate because its at its saturation point already. flashing of the condensate and rapid contraction of the steam is one cause of water hammer.

Certainly doesn't sound realistic to me.

pedmec

@ChrisJ Then you don't know what a flash tank is do you?

Jamie Hall

I'm going to assume that the near boiler piping is correct, but... is this single pipe steam? if so, one possible problem has to do with how the high level steam main extensions (often called dry returns, though they aren't) are connected at the boiler.

Can you clarify?

ChrisJ

pedmec said:

@ChrisJ Then you don't know what a flash tank is do you?

Isn't that the show with the 4 rich people that listen to ideas?

EBEBRATT-Ed

I think it unlikely that bad main vents would cause knocking. There is probably more to this story.

Dairon421

ethicalpaul said:

The pressure might have risen to a point that could cause water level problems.

did you skim it?

can we see the correct near boiler piping? It’s such a rare treat.

ethicalpaul said:

The pressure might have risen to a point that could cause water level problems.

did you skim it?

can we see the correct near boiler piping? It’s such a rare treat.

Jamie Hall said:

I'm going to assume that the near boiler piping is correct, but... is this single pipe steam? if so, one possible problem has to do with how the high level steam main extensions (often called dry returns, though they aren't) are connected at the boiler. Can you clarify?

One pipe 

Jamie Hall

Near boiler should be OK. That's something! I notice, however, an insulated pipe behind the boiler. What is that pipe?

EdTheHeaterMan

Is the flue connector (smoke pipe from boiler to the chimney crock) properly sloped at least 1/4" per foot going up from boiler to chimney? It looks like the pitch is the wrong way... But it may just be the camera angleOtherwise, The near boiler steam piping looks good. Nice Work!

ethicalpaul

Is it a single main with three vents on it, or are there multiple mains splitting off that one riser?

it seems kind of big to just have one riser, but it’s hard to tell from looking

Dairon421

Jamie Hall said:

Near boiler should be OK. That's something! I notice, however, an insulated pipe behind the boiler. What is that pipe?

That the return piping 

Dairon421

Dairon421 said:

Jamie Hall said:

Near boiler should be OK. That's something! I notice, however, an insulated pipe behind the boiler. What is that pipe?

That the return piping 

That may be the problem. I saw the water line surging 

Jamie Hall

So I expect that's the problem with the hammer. It is much too close to the water line. Either raise it at least 28 inches or drop it to the floor.

pedmec

i think the OP asked the question why changing the air vents stopped the system from banging?

Jamie Hall

pedmec said:

i think the OP asked the question why changing the air vents stopped the system from banging?

So he did -- and my guess, and it's just a guess, is that changing the venting changed the internal pressures just enough so that that pipe is just barely solidly wet, which would make the difference.

Dairon421

Yeah I found the problem. The problem was my Hartford loop tee wasn't low enough Below the water line. I thought it was supposed to be 2" below but the boiler I'm installing said 6" below water line. What was happening was steam was pushing back to my return and causing water hammer because the tee wasn't low enough 

ethicalpaul

6" below is odd but yeah it shouldn't hurt anything. Especially since the Hartford loop doesn't protect you to speak of anyway.