Vacuum at blowoff on low water cutoff?

BradHotNCold

2-pipe steam system; when blowing down low water cutoff I run into vacuum(!) so that instead of dirty water coming out, air goes in! Air goes into system and water gauge glass bubbles like crazy. After a while (30 minutes or so) automatic water feeder kicks on several times, and gauge glass then shows completely full of water. Try to drain water using blow down, and more air goes in before water comes out. With all that water coming in from water feeder, the radiator in 2nd floor bedroom (about half way around the house from boiler) does not heat at all. Blow water out, it does better at first, but then process starts up all over again. Any suggestions appreciated...

will smith_4

Vacuum at boiler

Does this system have vacuum return assist pumps? Is so, it sounds like you could have traps failed open.

BradHotNCold

Vacuum at blowoff on low water cutoff?

No such pumps...did have a busted steam line to one room, but plumber suggested due to age of syatem (100+ ??) and expense (busting out wall from cellar to second floor, repiping, etc.) that we cap lines for that room. As we are contemplating new system anyway, we did so. Problem persists...

Jamie Hall

Vents?

How are you fixed for operating vents?  When a boiler shuts down, the condensing steam will try to pull a vacuum.  However, if there is adequate venting (in a modern system now) the vents should let the air back in, relieving the vacuum.  Your whole description sounds like a system with no or very little main venting.  What can happen then is that when the boiler shuts down, a vacuum forms in the radiators as the steam condenses.  This will hold any condensate which is forming (which could be a number of gallons) up in the system rather than letting it return.  Which may kick in the auto feeder.  And when you open the skim or blowdown port, you are letting air in -- as you say, bubble bubble bubble -- until the vacuum is relieved.  Then the condensate returns and you are flooded.



Check your vents.