Water hammer.

charliechicago

Hello to all.
In regard to what Dan describes on page 27 in the lost art about a new boiler and turning a wet return into a dry one, if there is no vent at the end of what used to be the wet return, how would steam get their?
Thank you, mike.

Fred

Why/How did you turn a wet return into a dry return? I think we need to better understand what you are trying to do or have done and see a couple Pictures of the new set up. Steam really shouldn't get into a return. Is this a 1 pipe or 2 pipe system?

Jamie Hall

The problem with turning a wet return into a dry return isn't so much steam getting into it as it is pressure. Most -- if not all -- wet returns have drips from the steam main. Commonly at the ends, if nowhere else. There are also drips from the dry returns. Now if the steam main drips are isolated from the dry return drips, the pressure in the steam main --- which may be small, but it's what's getting steam to your radiators -- does not affect the pressure in the dry returns -- which should be zero or awfully close to it, if the vents are working. Given that, steam will able to flow into the radiators while the air flows out into the dry return, and you have heat.

But

If that water seal isn't there -- what should be a wet return isn't -- the pressure in the steam main gets into the dry return immediately, and you lose the pressure difference across the radiator which makes the steam flow. Presto -- no heat.

Not good.

Now you may also get water hammer in a return which was wet but is now dry. Wet returns aren't affected by sags and dips which can trap water, but if they are now dry, and water collects, as soon as there is air flow in the return it is going to pick up that water and slam it into the next handy obstacle downstream.

So now you have a system which doesn't heat as well as it should, if it heats at all, but one bangs.

charliechicago

Thank you guys very much for responding. This is only a theoretical question based on what I read in the lost art. Did the picture pop up on my page. The case is where the replacement boilers water line is much lower than the original and it turned a wet return into a dry one. But if you look at the picture or just imagine a now dry return with no air vent at the end, I don't understand how steam could get there. It's like a main with no air vent. I like to understand the concepts so I can apply it to other cases , even though this is not an actual job. Thanks again, mike.

Jamie Hall

There will always be a vent on the dry return somewhere. Has to be.

charliechicago

Yes, but in this theoretical case when the boiler was changed a wet return was changed into a dry one. I tried to attach a picture again. Thanks