One of the biggest problems with oscillators is maintaining a seal between the cylinder and the mainframe to allow the passage of steam to the cylinder between two sliding faces. Very early marine design actually used oscillators in ships and got away with it as the boiler pressures used at the time were relatively low.
As power requirements increased however and boiler design improved the steam pressures started to rise and the problem with the sealing face became more of an issue. The answer was to incorporate a valve in a chest alongside the cylinder which directed the steam to the cylinder at the appropriate time. The valve was driven by an additional throw on the crankshaft and the rod that operated the valve was relatively easily sealed by a stuffing box. The cylinder no longer oscillates, so those associated losses are removed, and the steam pressure can now be raised giving more power for a given volume. Most slide valve engines are double acting as the valve is used to direct the steam to both sides of the piston so, unless the engine stops at top dead centre or bottom dead centre, it should self start. Another major advantage with this engine is that the steam admission can be timed and adjusted so steam can now be controlled in a way that an oscillator could never achieve.
The first picture is probably one of the most popular of model vertical slide valve engines and that is the Stuart 10V. This was also an Ebay buy but part of a complete installation that incorporated two vertical engines, one with an upside down crank, a horizontal engine, boiler, feed pump, dynamo and a lamp. This is obviously very old and from the time when well to do people bought toys to demonstrate a few of the principles of physics to kids. Anyway I purchased it with the intention of restoring the whole set up one day but there is certainly a lot of work required for that. All the items are Stuart though so there is a ready supply of spare parts available for these things so, hopefully one day, it will all become a working model again. Probably one for the retirement fund!!
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“Dirty British coaster with a salt-caked smoke stack, Butting through the Channel in the mad March days" |