A large vertical coal-fired multi-tube boiler, mounted on a steel base with castors for moving it around. The boiler is coupled to an Elliott & Garrood steam pump, with all pipework for pumping water and complete with pressure relief valve on the feed side of the pump. 50psi working pressure, feed by injector - there is a spare clack valve which could be used for a hand pump (or, indeed, the output of the steam pump).
Nicely put together, the boiler would also be suitable for powering a number of large model stationary engines. We've had it running in the yard - there's a clip here - it pumps water effectively and will sit at a steady 50psi as long as you keep putting coal in it.