Maybe the pistons are offset to give two rows.  I have a 'Pistonola'
of my own design.  When I bought my piano it was not a player, so to
do something different (I had heard of the Pistonola) I made my own,
using two racks, each one offset .

The pistons have "O" rings for the seals and are 1-1/2" diam.  20" H2O
water gage suction gives approx. 3.2 pounds force.  I am thinking of
featuring this in the AMICA magazine if they so desire, plus my
perforator.

Steve Bentley