Friday, April 30, 2010


It looks like a cross between a castle and a mechanical spider; if I had been shown an uncaptioned picture, I would have been convinced it was a movie prop.

But it's real: Cruquius, the largest single-cylinder steam engine ever built, a Cornish Engine far from Cornwall. And it's big: the primary piston is 144" in diameter. On the official site, there's a page with a video that follows a reporter inside the main cylinder.

Restored but not under steam (the boilers are long gone), nowadays, the engine is moved by hydraulics; but move it does and it's an image you're not likely to forget.

What did it do for a living? Why, it helped drain the Netherlands!


  1. This is really a strange machine! We have to wonder just why it is arranged in this fashion. The engine operates almost like a Newcomen engine (well, night quite, there is positive pressure pushing the piston in both directions, not relying on vacuum), with a really strange concentric cylinder design. The machining specs must have been pretty difficult, especially at those large diameters. They don't give the steam temps, but the boiler pressure was only 45 psi (presumably gauge), later bumped up to something like 68 psig. That suggest that the cylinder walls did not run extremely hot so thermal expansions were not too big.

    One of the real oddities is that it appears that all pumps operate in phase, so there is no attempt to have a steady operating load. This is consistent with the lack of a flywheel or other energy storage device, but it would have made the whole thing look like it was breathing!


  2. If you start with a straight Cornish Engine, it makes (a little) more sense -- those typically have one pump, and a wall that supports the pivot of the beam. This is the same thing, scaled up and multiplied.

  3. I tried to follow the valve operation and it made my head hurt.