Boiler Flooding Itself

Premeric

I have a 7 year old Ajax atmospheric boiler that is being used in a brewery. It works very well, however when I shut it down, the system cools off and pulls a vacuum from the feed tank and completely floods the system. The next morning I have to drain off quite a bit of water from the boiler to get it to the proper level. I've never seen a vacuum relief installed on a boiler, but I'm beginning to wonder if that's the answer.

Any advice is greatly appreciated!

Jamie Hall

Well... has it always done this? For seven years? If not, the first question is what has changed -- or failed? Just looking at fundamentals here, if we start with a cold boiler and system, then there must be air in all the piping which isn't actually filled with liquid water. When the boiler fires, that air has to go somewhere -- so presumably there are air vents on there someplace. In most cases, those vents do not -- and are not supposed to -- seal against a vacuum. Therefore, when the boiler shuts down and the steam condenses, the vents should let the air back in.

So... if it hasn't always done this, sounds like either something failed -- like the vents are stuck -- or someone did something creative which blocked the vent action.

Yes, a vacuum relief would -- obviously -- fix the symptom. But it would be better to fix the problem if you can find it.

Pumpguy

My usual recommendation when this occurs on a steam heating system is to install a motorized valve on the discharge of the boiler feed pump. This valve is wired in to the water level controls on the boiler so the valve only opens when the boiler calls for water and activates the feed pump.

With the valve closed, the difference between the pressure on the steam side, which is now below atmospheric, and that in the boiler feed tank, which is at or above atmospheric, won't allow atmospheric pressure to push feedwater into the boiler.

On a steam heating system, the vacuum is usually desirable, so a vacuum relief valve would not be recommended.

For your process application, a vacuum relief valve might be the best option.

You understand of course that the vacuum comes from condensing steam in the header and boiler. When this steam condenses, the volume shrinks by a factor of 1/1700, so a very deep induced vacuum can occur.

dopey27177

Typically where vacuum is not needed or required a boiler vacuum breaker will solve the problem.
The vacuum breaker can be a swing check valve with a soft seat. The check valve is installed on top of the boiler trim and a 1/2" swing check is suffficient. Normally according to Hoffman condensate pump installations calls for a connection between the steam side of the system and the return side of the system where a check valve is installed to equalized the return and steam side when steam is no longer produced for any heating or process need,

The check valve installed at the boiler trim is the most econamical install for your needs.

Jake