Just screw the bottom valve plates on dry, making sure they sit
squarely, and then carefully apply a meniscus of PVA (_not_ PVC-E!)
round the bottom inside periphery of the valve well to get a perfect
seal.  PVA is also an excellent sealant for any porous wood.

PVA will never shrink, crack or flake into bits which can get into
the valves, is much easier to use than shellac and can always be
removed without damage.

It's worth noting that the valve travel of the 4 valves (8 on regular
Duo-Arts) is different -- the power 8 certainly needs more travel.
But anyway, though the travel must be minimised for quietness, the
accordions should be able to open and close as quickly as note
pneumatics to follow the signalled dynamics, especially on early and
UK rolls.

Patrick Handscombe
Wivenhoe, Essex, UK