Your thoughts on using.....

PDB2

1 1/2" pump flanges face to face with flat gaskets instead of unions or threaded fittings. I am building a different manifold setup on my near boiler piping and the thought occurred as an easier and more serviceable connection. Regular 4 bolt flanges would seem a little overkill and spendy...I already have the extra pump flanges, just wondering if the flat gasket are as dependable as a groove o-ring seal like on pump mounts.

I've never seen an example of this being done and am hoping some of you can gently explain why :)

Gordy

I would think

It would make a weak connection. It's a more solid connection with the pump side backing up the flange fitting. Bolting two together as you describe would not be as solid as a 4 bolt style.