Undersized boiler feed tank

Weil

I am following a two year old installation by another contractor where they installed a shipco DM260 boiler feed tank. On mild days it will dump up to 150 gallons out of the overflow per day. The engineers are asking me to install an additional condensate tank tied to the DM 260 with equalizing piping to increase the storage capacity. Thinking this through my question is instead would it be better to...
Install that second condensate tank interconnected only by the overflow so when the boiler feed tank overflows it will fill the second tank. Then when the boiler feed runs out of water and calls for makeup water we can actuate the pump on the second tank to feed it. I would also put a time delay on the fresh water makeup giving it time to utilize what was in the second tank before it feeds.
Any help is appreciated.
Weil

deadmansghost

It would be best to install the new tank the way the engineer wants it.

DickC

Sounds to me like someone should first be checking the sizing of the tank and boiler. If this was done correctly originally, why is this overflowing? Is the tank feed leaking by? Something does sound right. What size s the boiler?

Pumpguy

What type of make up valve arrangement does this unit have? It could have either a mechanical internal float valve, similar to a toilet water closet, or a float switch and solenoid valve.

Do you have any information about the steaming capacity of the boiler?

Typically, boiler feed tanks are sized to provide a certain amount of steaming time before condensate returns and replaces what the boiler has steamed off. This steaming time typically ranges between 10 and 20 minutes. I would say if, based on how much water the boiler can boil off, if you have much less than 10 minutes of steaming capacity, the tank is too small.

If you feel you want to add to the capacity of your boiler feed tank, I would suggest you follow the engineer's recommendations. I have made similar recommendations in the past.

The real question is, where is all this condensate coming from?

Obvious source would be from leaking make-up valve. Mechanical make-up valves are pressure sensitive and typically aren't recommended for use above 45 PSI supply pressure. If pressure is much above this, then a PRV should be used.

Another thing to consider is non-functioning or missing equalizer line(s) between steam header and return line(s). If equalizer line is plugged, or check valve or thermostatic trap is not opening, then the vacuum caused by condensing steam on the steam side of the system could hold up a whole load of condensate. Only after the system equalizes, or comes up to steam pressure will the held back condensate flow back to the boiler feed tank.

If this is what's happening, you will continue to see starve - then - flood conditions at the boiler feed tank until the issue is resolved.

On mild days you would only be making steam on a part time basis, and this problem is more likely to happen if there is an equalizer problem.