Sucking Steam Vents and Clanging radiators

Tom Zydowsky

Hi All,

I have a 15 year-old SlantFin single pipe steam bolier. Recently I've noticed that several of the my radiator steam vents begin to suck in air about 5 minutes after the boiler shuts down. Any thoughts on what's causing this?

Also, I have several radiators (not the ones that suck air) that produce a bell-like noise about 5-10 minutes after the boiler shuts down. Any ideas?

Are these events related?

Thanks,

Tom

gerry gill

since its happening after

the boiler shuts down, i'm wondering if the main vent(s) are not opening to break the vacuum..do you have main vents?

Tom Zydowsky

Yes. About three weeks ago I installed two #1 Gorton air eliminators on the front (45') main and one #1 on the rear (20') main. Before that I had one Hoffman #41 on the front and one Gorton #4 steam valve on the rear (left from the previous owner).

I checked the main vents and couldn't hear anything like the noise I hear from the rad vents. The rads are on opposite ends of the top floor in a two-story bldg and right above the main vents.

Thanks

Steamhead

Check your steam pipes

if they are not insulated, steam will condense in them and cause a vacuum when the boiler shuts off. This will cause the vents to pull air in.

The bell-like sound is the cast-iron radiators contracting as they cool. It's normal- my hot-water radiators do the same thing.

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Tom Zydowsky

Steam Lines

Steamhead,

I insulated my steam lines and will see if that helps.

Thanks to you and Gerry for suggesting ways to eliminate my vacuum problem.

Tom

Dave Meers

radiators sucking in air

Hi Tom,

It is normal for the one-pipe radiator vent to draw some air back into the system after the boiler shuts off. The old timers used to try to prevent that from happening when systems were fired with coal. The theory was, keep the system in a vacuum and the boiler could make steam at lower water temperatures as the coal fire died out at night. This doesn't work with automatic gas or oil fired burners, so we let the air back into the system during the off cycles.

The noise is probably as Steamhead describes, expansion noise.

Best regards, Pat

Fred Harwood

Hot Vents

If the Gorton #1 vents can't cool below about 140 between cycles, they don't reopen. That will cause the collapsing steam to pull air through the rads. Ensure that your Gorton main vents are well away from the insulated main, perhaps on 18 inch stubs.