Pianolas are much more complicated than what can be seen from the outside, there are hundreds of moving parts hidden inside. All the pneumatics and bellows are covered in rubberised cloth, valves and gaskets are leather and tubing is also rubber. All these parts have a lifespan of around 30 years and need to be replaced when they are old and rotten.
The pianola action generally consists of a unit in the bottom of the piano which produces the vacuum called a bellow set, which has feeder bellows attached to pedals and reservoir bellows which are spring loaded,
and a top action with 88 small pneumatics (bellows) which activate the piano keys. Each of these small key pneumatics is controlled by a valve (or two in a double valve type) which is activated by a hole in the roll as it passes over the tracker bar.
There is also a system of tracking to keep the roll aligned with the holes and an air powered motor to drive the roll via a gearbox, a governor to regulate the air motor speed regardless of pedal pressure, and often other pneumatic/valve units for sustain and soft hammer rail.
Link to which brand of player mechanism is inside your pianola Player piano makers
For information about buying a pianola Pianola buying guide
Reinstalling newly leathered valves in an Aeolian
Valves and pneumatic of a Beale Bijou
Standard action from a Concord showing primary valves above the secondary valve and pneumatic unit.
A more complicated electric pump driven Duo-Art Pianola.