In foot-pump use the Pedal-Electric Duo-Art [PEDA] works exactly like a standard Pianola and needs very little pumping effort (assuming it's airtight, of course).  The "Theme" half of the Duo-Art expression box cuts out automatically, and the Pianolist only has to pedal the accent level, leaving the expression coding to provide the Accompaniment level automatically.

For the technically-minded, the expression box has two separate Theme valves in it: one for automatic playing where a Theme accent switches between the regulated Accompaniment suction and the regulated Theme suction, and a separate valve for foot-pumping where an accent switches between regulated Accompaniment suction and the main unregulated (foot-pumped) suction supply.

Have a look at my web page that gives some details about the system; it's from an article I wrote many years ago for a magazine.  I don't offer a diagram of the expression box innards, but detail the tubing of the control logic and bits otherwise hard to find.

http://www.pianorolls.co.uk/Understanding%20the%20Pedal%20Electric%20Duo-Art.htm 

These instruments are commonplace in the UK, easier to find than the electric-only version.  The expression boxes I'm used to differ in detail from the standard American production but the logic should be the same.  I've never seen a US-made PEDA, though.

Julian Dyer