16. MSM Engines - Explained

16. MSM Engines - Explained

Introduction to Engine Design Terminology:

It is assumed that the reader does not need an description of the internal components of an engine and their basic function -  e.g. piston, cylinder, crankshaft …..etc. This guide is to set out a description of some supplementary steam engine terminology that may be of help in understanding how to run and maintain an engine.

Both MSM engine types are designated as “double acting” in that power is generated by high pressure steam being admitted by a valve system working on both sides of the piston so that while one side of the piston is being driven by the steam the other side of the piston is exhausting the spent steam from its previous power stroke. Thus there are two power inputs for each turn of the crankshaft.

An “oscillating” engine valve system operates by the cylinder rocking sideways on a pivot to expose one side of the piston in the cylinder to high pressure steam delivered from a port in the engine trunk while the spent steam on the other side of the piston is exhausted through a separate port in the trunk.

Again there are two power inputs for each turn of the crankshaft.

A “slide valve” engine has a valve system that operates in a sealed chamber supplied with high pressure steam. The steam  is admitted to the cylinder through a port into the cylinder that, on a power input, is opened to the pressure by a “slide valve” The longitudinal movement of the slide valve is controlled by eccentric cams fitted to the crankshaft of the engine, connected to a “valve rod” that passes into the steam chamber through a sealed “gland”. The slide valve has a recess cut into its side facing the cylinder so that while high pressure steam is entering one side of the piston the slide valve covers a second port to exhaust spent steam from the other side of the piston.

Twin cylinder engines are designed to be “self starting". This means that at any position of the crankshaft steam is able to enter a cylinder and start the rotation. This is not necessarily the case with single cylinder engines. If the engine comes to rest with the piston at the top or bottom of its stroke it will require a “nudge” to the flywheel to position it where pressure on the connecting rod is able to lever rotary action on the crankshaft and start it rotating. Once started it will continue until the steam or gas runs out.

Thus Radio Control (RC) features are only available on twin cylinder engines.

The whole MSM engine range is suitable for static installations where the “nudge” is readily available when needed.