Do steam piston engines actually do any real work anymore?

Not fully retired, but it's close. The one geniune working example I know of is a coal-burning passenger ferry on the Great Lakes that still crosses Lake Michigan every summer season with its original triple-expansion engines, because fitting diesels into a 1950s hull never penciled out financially. So it's earning its keep, just barely, and mostly on sentiment and sunk cost. Where I actually ran into live steam pistons was in refinery work. Direct-acting steam pumps, the kind with no crankshaft at all, just a steam piston tied straight to the fluid piston. A few of those were still in daily service on boiler feed and hot oil duties. The reasons they survive are pretty practical: the plant already has steam everywhere so the 'fuel' is free at the point of use, there's no electric motor sparking away next to flammable vapors, and they'll sit stalled against a shut discharge valve all afternoon without burning anything up. An electric pump in that spot either trips or cooks itself. Slow, heavy, near-indestructible, and they can sit there thrashing for fifty years with nothing but packing and valve upkeep.

Beyond that you're into the edge cases people mentioned. Sugar mills in cane-growing countries burn bagasse for boiler fuel, and some of those still run old steam reciprocators driving the crushing plant, since the fuel is basically waste and efficiency doesn't matter when heat is falling out of the sky. Small combined heat and power setups in Europe also sell compact steam engines that fit somewhere a turbine is too fussy, using the waste steam that a factory was going to vent anyway.

The general crossover point is low horsepower. Once you're past a few hundred horsepower the turbine wins on efficiency and maintenance every time, and below that the world mostly just uses electric motors now. So the niche got squeezed from both ends. Your pumping station engine would have a modern equivalent, it just wouldn't be a piston, it'd be an electric motor on a variable drive. The old iron survives where steam was already lying around the site and nobody had a reason to rip it out.

Spent a stretch in the 70s in a textile mill that still ran a big Corliss on line shafting, overhead belts going everywhere. The rule was the engine never stopped, it just idled down between shifts. What stuck with me was the governor work and the valve gear, all levers and links, and a fitter could fix nearly all of it with a file and feeler gauges. That's the thing about those engines, the maintenance skills were common as dirt back then. Now you'd struggle to find a bloke who's even seen a Corliss running, let alone one who can time the valves by ear like the old hands used to.

New here so hope this fits, but the last working one I ever saw in person was a steam donkey engine at a logging demo, dragging logs around with a wire rope, and even that was running on a caretaker's donations more than anything. What I keep wondering is whether anyone still builds small ones new. I mess around with old farm tractors and there's a whole hobby supply chain keeping those parts alive, so it seems odd that nobody makes a modest modern steam piston unit for the odd off-grid spot where you've got biomass and no grid. Or is it one of those things where the boiler rules and insurance kill it before the engineering ever gets a chance?

They still turn up as emergency backups. I spent a few years at a paper mill that had a big cross compound driving a generator as a standby power source, and we bumped it over once a month to keep it honest. Ran at about 180 rpm and you could feel it through the floor from two buildings away. The logic was that if the grid died, we still had boilers making steam, so we still had shaft power. Whether anyone ever actually threw the switch in an emergency I doubt, but it sat there fired up and ready all the same. Curious what happens to machines like that once the last crew who knows the startup sequence retires.

Gotta push back on the refinery bit though. I worked in a couple of chemical plants and the direct-acting pumps were mostly long gone by the time I got there, swapped for electric or air-driven units years back. The few that hung around did so becuase ripping them out meant redrawing the piping docs and redoing the hazard review, not because they were the best tool. 'Steam is free at the point of use' is the part I'd argue with too, nobody accounts for the boiler water treatment and the guy keeping the steam side alive. I'd bet money that if you toured those same plants today you'd find maybe one left running, and even that one's on the decommission list.