vacuum in steam boiler

Steve_57

I replaced a 900,000 Btu steam boiler that serves a wood drying kiln. The boiler is connected to a steel fin coil blower unit. We piped the boiler as specified and it works well, in spite of some grossly under sized returns which we will be replacing.
The problem is the vacuum that develops on shutdown. It will pull 10" as the steam condenses. One problem it creates is that it sucks the water out of the make up tank, and overfills the boiler.
So what's the best solution. Should I put some type of vent on the fan coil other than the F&T trap? Any help would be appreciated.

Steamhead

A Vacuum Breaker

is the solution here. Mount it on or near the boiler (on the steam side) so the vacuum will be broken as close as possible to the return line connection to the boiler. I think Hoffman makes one but can't remember the model- maybe #61 or #62?



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