I disagree........that's a double acting cylinder. Otherwise, why would there be two two petcocks to release water until it heats up? If you watch (and listen) to it running, it definitely has two power impulses.
All that, plus it appears the entire Listeroid cylinder has been replaced with one suitable for a piston valve. This may be "nothing more" than a Listeroid converted to steam, but it's really pretty clever and utilizes an already proven platform (base, crank, flywheels).