Uniflow steam engine

Steam entry is usually controlled by poppet valves (which act similarly to those used in internal combustion engines) that are operated by a camshaft.

These ports are connected by a manifold and piping to the condenser, lowering the pressure in the chamber below that of the atmosphere causing rapid exhausting.

From the animation, the features of a uniflow engine can be seen, with a large piston almost half the length of the cylinder, poppet inlet valves at either end, a camshaft (whose motion is derived from that of the driveshaft) and a central ring of exhaust ports.

This causes the opening times of the inlet valves to be very short, putting great strain on a delicate mechanical part.

In order to withstand the huge mechanical forces encountered, engines have to be heavily built and a large flywheel is required both to smooth out the variations in torque as the steam pressure rapidly rises and falls in the cylinder and to compensate for the inertia of the heavy piston.

If the cylinder is not heated correctly, or if water enters, the delicate balance can be upset causing seizure mid-stroke and, potentially, destruction.

[3] Only one such steam wagon is known to be still in existence; it was built in 1918, spent its working life and a period of dereliction in Australia, and was then repatriated to England and restored by Tom Varley in 1976-77.

A non-compound Skinner Uniflow remained in service until 2013 in the Great Lakes cement carrier SS St. Marys Challenger, installed when the vessel was re-powered in 1950.

White Cliffs Solar Power Station used a three-cylinder uniflow engine with "Bash"-type admission valves to generate about 25 kW electrical output.

[6] As the rising piston nears the top of its stroke, it knocks open the bash valve to admit a pulse of steam.