feed water

steam247

why do we sometime put the feed water line at the compression tank on hot water boiler and others with a feed water/ cut-off combination. i understand by the tank is the place of no pressure change.  looking to understand why we sometimes don’t put it at the tank and put a combination feeder/cut-off instead off return.

PC7060

@638Jay - “looking to understand why we sometimes don’t put it at the tank and put a combination feeder/cut-off instead off return.”

I’m not tracking, do you have an picture or drawing of this configuration?

neilc

because sometimes the manual doesn't get read

EBEBRATT-Ed

@638Jay

You want the feeder (pressure reducing valve) and expansion tan to "see" the same pressure. The air pressure in the expansion tank and the feeder pressure should match.

Other than that I have seen many jobs where the feeder is connected in a different location and it works fine as long as there is no appreciable pressure drop between the ex tank and feeder it will be fine.

Example:Putting the expansion tank on one side of the circ pump and the feeder on the other would be a bad thing

steam247

steam247

the top pic has feed water at tank and bottom pic has a combination feed water/ LWCO . looking to understand why and when. most books say to have it at tank “ point of no pressure change”  . but i see it also the other way 

EBEBRATT-Ed

@638Jay

Like I said in my first post. It dosen't matter. As long as the expansion tank and the PRV feeder are seeing the same pressure it's fine

In the bottom picture they are feeding water into the bottom of the boiler and the expansion tank is connected to the top of the boiler

With a cast iron or steel boiler they are basically like a big tank full of water.

There is negligiable pressure drop between the two points so it's fine

If we were talking about a mod con boiler it would be different

Connecting the tank together with the water make up is always a good thing to do. Just because someone did it differently doesnt mean it's wrong

steam247

thank you , yea depending what page you are on in a text book lol. most book say put feed water on line that connects the tank. but when you get to the page on LWCO it shows it this way and never explains why it’s different.