Been still mucking about with the pop safety valve experimenting with different cup diameters. I took 1 thou cuts off the first one until it didn't pop anymore which was about .017" diameter clearance between the cup and the secondary seat.
I have another pop valve drawing which stipulates a .006" clearance but only has 4 exit holes at the top. I made some years ago which have .006" clearance and they seem to work OK.
Still getting ~10psi difference between lift and close and have a few more experiments tomorrow. I've changed the way I made the cup and spindle...both have threads but decided to do it into a blind hole rather than a through hole. The difference was the end of the stainless thread and brass being two different metals had shown that it was pushing the ball to one side once it bedded into the cup after a little bit of operation. The tangent point where the ball was sitting was on the end of the thread. Also found the seat in the body needed a cleanup with the seating tool as the ball had made its own sweet spot on the square edge and flattened it a little.
Happy steaming!
Nigel
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