TargetTalk

If you look at the diagram:
the rearward force of #17 on the valve sear (#14) wants to push #14 down. When the pistol is cocked, the top end of the trigger sear (#15) prevents #14 from pivoting down. Once the trigger sear is released, the force of #14 on the angle at the top of #15 should push that to the rear, releasing the valve sear. The spring on #15 should help, but I'm not sure that it is essential. It depends on the exact angles & how smooth & lubricated things are. That spring isn't very strong to begin with.

If #15 isn't pivoting back to release #14, either there isn't enough rearward force from #17 to make #14 slide down the ramp at the top of #15, or possibly there is too much friction on the ramp at the top of #15. That could be caused by wear, a burr, or inadequate lubrication.

@Gwhite

Trigger sear #15 is the problem

When dry firing with breech cocking lever closed, trigger sear #!5 moves well, plunger shoots back nicely after trigger sear release

But when cocked from air piston lever, via breech link system, trigger sear some how gets stuck, won’t move. I had to manually push that trigger sear upward , the pistol discharge.

Trigger sear is getting stuck as you mentioned in your PDF, but not stuck with dry fire manual breech lever cocking. Why does trigger sear get stuck when the whole thing is cocked through piston link?

What would happen if I file down
that notch block on top of trigger sear, that seem to the place where trigger sear gets stuck.

That's a new one...

Have you tried greasing the top of the trigger sear?

The impression I have is that there is a certain amount of hand fitting that goes on when they build one of these. It's possible they didn't quite get something right, but it it worked fine before, it's more likely a weak spring or loss of lubrication.