I have built up a 3D CADD model of Climax CN 1551 which at present has over 10,000 parts. A question has arisen about the amount of Valve Travel which would be expected (typical) for a Slide Valve Cylinder. So that one can visualize the process the Climax Cylinder has a centered Exhaust Port 13.5" Wide by 2" Long. The Intake Ports to the front and rear of the cylinder are 13.5" Wide by 1" Long and separated from the Exhaust Port by a 1" Land on both sides. The Cylinder itself is 14.5" x 16".

I did an experiment in my 3D CADD model of 1551 to see if I could determine the Valve Travel.
With Johnson Bar (Reverse Bar) in the first notch (of 5 forward, Center, and 5 reverse) in the radius ahead of Center, the Valve Travel is 1.375".

With the Johnson Bar (Reverse Bar) in the furthest forward notch (Number 5) the Valve Travel is 1.50".

All the interconnected parts are based on Climax drawings (except for the nocked radius and the Reach Rod which I very carefully recreated) so the geometry is probably closer than Climax achieved back in 1919. (Based on working on 1551 for 6 years and long conversations with the project foreman).

Is that variance between the two positions typical? Is the Valve Travel in the expected range?

A further question is what determines Maximum Valve Travel. I have see a Shay Equipment List which listed the Maximum Valve Travel as 4.75" - Piston Valve?

Hope there is someone out there who can "educate" me.

Thanks in advance.

Many slide valves were built on the principle that extremely short stroke gave the least trouble with lubrication and inertial forces. This often resulted in amazingly long transfer ports to the cylinder ends. Where more admission was desirable, some form of multiple Trick porting could be used.

High-speed locomotives could nominally benefit from a riding cutoff, which was like a second valve running on the top surface of the valve, with the counterpressure applied on top of it instead of the valve. This allowed very fine cutoff of the steam without having to try to move the Johnson bar with the required precision but still allowing quick change or reversing when wanted. If you see reference to the Cuyahoga Cutoff, this was a famous marketed version.

By 1914 I'd expect slide valves to be increasingly 'out' in favor of piston valves (and radial valve gear instead of eccentric-driven link) so refinements to the valve gear might have been deprecated in favor of relative reliability in poor maintenance conditions.

I would suggest to use a simulator with your dimensional data to inspect how it works.
http://www.jf2.com/bcwrr/Dockstader-Valve-Gear.html
Kind regards

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Based on the comments and my drawing which is a 2D projection of the 3D model, the Maximum Valve Travel would be 3 21/32". The 8" Radius of the Crank Rod in correct for the Cylinder 16".

Am I understanding correctly the comments?

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There are probably other ways to go, but these rules have worked for me:

The valve travel is the width of the steam port (in your drawing this is 1") plus the valve lap (1/2 the width of the steam port) times 2.

Valve Travel = (Width of Steam Port + Valve Lap) X 2

Valve Lap = (Width of Steam Port) / 2

Inside Width of the Valve = [(Width of Steam Port + Width of Bridge) X 2] + Width of Exhaust Port

Outside Valve Width = [(Width of Steam Port + Valve Lap) X 2] + Inside Width of Valve

The bridge is the material between the steam port and the exhaust port.