In regard to Autopiano valves: often these secondary valves on the
Autopiano stack become bent or warped and they will not seat correctly.
You must make sure that the metal discs are flat and that the valve
travel distance is correct.  Make sure that the bottom and top valve
seats are clean and smooth, so that the leather seats firmly and seals
well.

I have had problems with Autopiano secondary valves that had fibre
discs, and they were warped very badly, causing no end of pumping
problems until their problem was discovered.

Good Luck.
Jim Jelinek