Equalizing line

Bruce_29

Ref a vacuum steam heating system with an equalizing line between the condensate return system and the boiler steam header. Mechanical vacuum pump to generate the vacuum.
Why is the check valve that is installed in the equalizing line in a water loop seal (trapped) below the horizontal line elevation by about 6" of the pipe itself?
I have heard to keep a better seal between the seat and check valve disk, it will remain cleaner then if it was in the steam line as contaminants might be deposited on it, the 6" gives you a differential for proper operation, to prevent the disk from chattering, etc.

Pumpguy

The purpose of the check valve in the equalizer line being dropped is to trap some water so the valve seat becomes water sealed.

Not often seen, but equally effective is a thermostatic radiator trap at the end of the uncovered cooling line where it drops down to the return line.

See attached illustrations.

Bruce_29

@Pumpguy Were the illustrations you attached from NASH literature and if so is the literature still available?
So if the check valve was not dropped it would still work but would have more of a tendency to leak?
Thanks for your input

Pumpguy

@Bruce_29, yes, most of the literature I have came from Nash. I have most of Nash's engineering and installation drawings. Most are post 1950, but some are earlier.