Normally, you slide the Themodist levers over to mute, the operation
being the same on Themodist and pedal-operated Duo-Art instruments.
However, I've seen one variant which operates in Themodist mode by
default, where the Theme levers introduce accenting.

The instrument I saw, which was in Australia, was a Pianola but with
a Temponamic control -- the only one I've ever seen on a Pianola (it
was for setting the accompaniment level).  That instrument introduced
the accents pneumatically, by letting air into the Theme accent lines;
the Theme sliders only had a very small movement, and operated a pallet
valve.

In an instrument that has slide valves to block the unrestricted air
flow, and you have to push these slides away from their rest position
to get unrestricted playing, I'd check that somebody's not simply
connected them the wrong way 'round, or has moved the springs to change
their rest location!

Julian Dyer