What is the secret to getting stainless balls to seal in small check valves, if there is one? Are stainless balls as round as bearing quality balls? Even new purchased clacks don't seal completely.
Give the ball a tap with a hammer to seat it into valve body. If the valve still leaks, discard the ball as it may now be damaged by the hammer blow and replace it with a new ball.
The seat needs to be perfectly round, drilled hole no good. Reamed or better still D bit. Having said that I use O ring seated valves, which do not leak. Anyone want the drawing send me a pm, no idea how to attach it to this site.