Yoke valve damage

[Bob DBF]

When I put a tank checker on there it blows air for a split second before sealing and not leaking at the 500# that's in the tank. That being said, it seals the 1st time about 50% of the time with no air leakage.

There are at least two different sized tank o-rings that I know of, if the wrong one is used, it will give problems initially sealing but work fine once sealed. Visually you can't tell them apart. Drove me nuts for a while, it was on an older Faber scuba pro branded tank and valve made for use with a manifold so it might have been a metric o-ring. Try changing it out could be its the wrong size.