Lost Art Pg 96 / 97

bean

I have a Question about a steam boiler flooding.How does it flood if there is a boiler feed tank controlled by a float in the boiler?

Noel

One way is it can have a problem getting air back into the boiler after shutdown and it will suck the water out of the tank and into the boiler.

Jamie Hall

Another is to have the float hang up or sink... they do, you know, now and then.

EBEBRATT-Ed

Defective float, defective pump control, plugged piping to pump control, bad check valve in feed water piping. Shorted wiring to pump control. Feed water control overfeeding boiler feed tank.

AMservices

I remember a funny story from @Dan Holohan talking about a tenant in a apartment building who had a problem with the maintenance man.
Every knight he would remove the air vent from a radiator in his unit, run a hose from his sink and flood the boiler.

DanHolohan

Yes, that was one creative tenant!

Pumpguy

To expand on @bean's comment, when the boiler stops producing steam, and it all condenses, we get an induced vacuum due to the change in volume between steam and water.

With the boiler feed tank being vented and at atmospheric pressure, the atmospheric pressure will push feed water from the feed tank into the boiler that is now at vacuum, and cause a flooded condition.

To prevent this from happening, there needs to be a positive closing valve on the outlet of the boiler feed pump. This valve needs to be wired to the boiler control so it will only open when the boiler is calling for feed water.

jumper

Vents are good to let air out. But ideally pressurization should be done with steam. Of course then you need some way to prevent feed pump from going on if tank is not pressurized. No knocks against Pumpguy: long ago pump vendors and control vendors made steam more complicated than it has to be.

Pumpguy said:

To expand on @bean's comment, when the boiler stops producing steam, and it all condenses, we get an induced vacuum due to the change in volume between steam and water.

With the boiler feed tank being vented and at atmospheric pressure, the atmospheric pressure will push feed water from the feed tank into the boiler that is now at vacuum, and cause a flooded condition.

To prevent this from happening, there needs to be a positive closing valve on the outlet of the boiler feed pump. This valve needs to be wired to the boiler control so it will only open when the boiler is calling for feed water.