Undersized Main Vent causing startup bangs?

matthewb84

Hi Everyone,

Quick question, I did some searching but can't find the exact answer on the forum. If I missed it, sorry for the redundancy.

I ironed out most of the kinks in my system but I am still getting banging at startup - lasts about 2-4 minutes starting a few minutes after the system kicks on.

Once it's over its pretty much done making noise.

Do you think this is water build up or is the main vent not flowing enough air? From what I can see everything is pitched correctly.

Jamie Hall

Somewhere out there... there is a low spot which is collecting condensate from when the pipes are first warming up and swooshing it into something. It's going to take some looking -- and may be just a sag rather than a real pie in the face low spot.

KC_Jones

Are you positive it isn't expansion noise? That can make a sort of banging noise.

1Matthias

I've had systems that water hammered to high heaven on startup quiet right out with the addition of proper venting. Most likely, the root cause is still a sag in a pipe, but it did seem to help.

Fred

If it Bangs, There is a pool of water out there somewhere. Slow vents don't cause banging.

EBEBRATT-Ed

What @Fred, & @jamie hall are correct. @KC-Jones makes a good point

matthewb84

I am guessing something is pooling, I will take out the laser level again. Is there a way to determine expansion vs water noise?

would water hammer/bang happen after everything has heated up?

Jamie Hall

matthewb84 said:

I am guessing something is pooling, I will take out the laser level again. Is there a way to determine expansion vs water noise?

would water hammer/bang happen after everything has heated up?

Be sure when you are using the level that you check the entire length of every pipe. It is quite possible for their to be enough sag in the middle of a longish run to produce rather spectacular bangs, even if the pitch between ends is correct.

Expansion vs. water noise -- can be difficult to distinguish, but expansion usually is more or a repetitive noise (although it can be one almighty bang) and regular and frequent, also more musical and not as loud, while water hammer tends to be less regular and more like someone hitting the pipe. But it can be hard to tell.

If it is indeed a problem with a sag type of pooling, it tends to go away once the pipe in question has heated up. Unhappily, expansion noises also go away once the pipe has heated up...