Stephenson Valve Gear

[MattMaie]

What goes into designing a Stephenson valve gear mechanism for any given engine? I want to build a small steam engine, basically out of any sort of scrap material I may have lying around my shop and I want it to be reversible and out of all the valve gears I have researched, the Stephenson gear seems to me to be the most straightforward to do for someone like me who is just getting into model engineering.

 

[kvom]

Piston valves are certainly easier to make than Stephenson, since reversing can be done by just swapping the input and exhaust ports via a valve.

 

[Jasonb]

A slip eccentric would be even easier.

J

 

[GWRdriver]

The first thing to do is read up. Googling Stephenson valve gear should bring up any number of descriptions in varying levels of complexity and you can become familiar with the parts of the gear. I find the Stephenson to be the easiest full function gear to design and make. There are a couple of versions of Stephenson gear which are typically different for locomotive, traction, marine, or stationary engine application. The basic components for the variants are essentially the same, the difference is in how the arms and links are configured and connected. There is a difference between valves and valve gear. Valves (piston or slide) are independent of the valve gear although slide valves are typically matched with the Stephenson gear. http://www.donashton.co.uk/Steph_Gear.avi

 

[Charles Lamont]

Piston valves are certainly easier to make than Stephenson, since reversing can be done by just swapping the input and exhaust ports via a valve.

Only with the crudest 'line-on-line' valve with no lap or lead, as you get with a simple oscillating engine too.