Steam return banging; Two pipe radiator

Daren

The house is over 100 years old, with original radiators and piping; Boiler was replaced back a few years ago. Two of the radiators are two pipe, third is one pipe. The problem is that when the system starts with radiators cold (for example in the morning) the condensate return pipe bangs in the basement. The return is 3/4 or 1 inch. I know the return pipe is clean. The return pipe comes to the boiler above the water level (see the picture). Could this be a source of banging? The previous boiler was water level was higher (old coal, then converted to oil). Will moving the return pipe below the water level help, or am I on the wrong track altogether... The boiler was flashed and 8-way was added. The funny thing is that it was fine right after the boiler was changed.
Radiators are on 2nd floor. Return pipe does not have any vents, devices, etc. just runs down, no sagging. There is a vent on the top of a larger vertical pipe, where return joins piping at the boiler.
Thank you.

Jamie Hall

"The return pipe comes to the boiler above the water level (see the picture). "

That's the problem. One of the rules when replacing a steam boiler -- particularly on two pipe systems, but also on one pipe if they have wet returns -- is that the water level in the new boiler must match, within an inch or two, the water level in the old boiler.

This is simply not optional. It is also something which never seems to occur to people, so your problem is not unique.

If that's the only return, however, fortunately the solution is simple -- although your installer may not be totally happy. Move the connection of the return to well below the water level. I even see a couple of handy unions so that the piping can be disassembled without cutting anything...

That radiator you picture looks as though your system may have been the two pipe with air vent variety -- very early. Is there a vent on that radiator?

Daren

Yes, there is a vent on the radiator on the return side. I changed all the radiator vents to new Vent-Rite adjustable vents, also all basement vents were changed. Right now I try to minimize the problem by keeping the vent on that radiator almost closed... And yes there are unions on all the sides where the return joins piping. It looks doable to move it below the waterline; The question is how far below? just below the waterline? more?, does it matter how much?

Daren

Jamie, I re-read your comments, it is more clear now. I will move the return down, well below the waterline. Thank you!

dopey27177

your two pipe steam systems is governed by the rules for a one pipe steam system.
The system you have needs no steam traps but needs vent valves on the over head returns in the basement. All overhead returns must separately connect to the wet return. Additionally operate the system at 1/2 PSI on and 1 1/4 psi off for the best results in fuel and operational efficiency.

Jake

Daren

Jake, that is what the boiler is running at. Thanks!

neilc

is there a skim port?
the water looks pretty bad,
and more pipe work will add to the dirty oily condition,
skim port ?

Daren

No, there is no skim port; There is only a drain port. I was thinking of degreasing the new pipes before assembly, and not trying to skim or flush. Not much pipe will be changed.
Yes, the boiler water is not very clean; It will be flushed and then 8-way added. It was recently flushed, but because it was running without water treatment previously it probably will take a few more water changes to get fully clean.
I'm really looking forward to getting this solved Nothing more aggravating than waking up and anticipating pipe noise in the mornings .. ha ha ha....

Jamie Hall

Watch out for the boiler treatment. First, don't overdose. Second, and perhaps more important, use it to clean the boiler -- and then get rid of it. Some water supplies may need a small amount of treatment to control pH; otherwise most steam boilers are much happier with no treatment at all.

EBEBRATT-Ed

Two pipe air vent is always an issue. Hard to control

Daren

An update: repiped to make the wet return below the water level of the boiler and the problem is gone!
The whole past winter, not a single bang.

Steamhead

Thanks!