William (3.5 Gauge)

Overview
William is a 2-6-2 Freelance tank locomotive designed by Martin Evans. It was serialised in Model Engineer magazine Volumes 149-152. It is an elaboration of his "Rob-Roy" locomotive.
 * Designed in ME 149-152
 * Length: 31.5"
 * Boiler Dia: 4"
 * Cylinder Bore: 1.125"
 * Driving Wheel dia: 3.75"

Prototype
The design broadly follows the design of the LNER V1/V3 locomotives used on passenger routes in the north of the United Kingdom. There are some detail differences, notably the pipework around the smokebox. The V1 and V3 were three cylinder designs (William is a two cylinder); the V3 used a superheater and a higher boiler pressure.

Details of design
Intended as a beginners engine there are certain design characteristics intended to assist.
 * Simple boiler design and construction
 * Slide valve operation
 * Outside cylinders and Valve gear
 * Split smokebox allowing access to the superheaters etc.

The locomotive uses three water tanks; two either side (one of which contains the hand pump) and another under the coal bunker. The water is primarily supplied to the boiler via an axle pump on the driven axle. There is a single Water gauge glass.

Blowdown valves are provided on each side of the boiler just above the foundation ring. There are two safety valves, usually the working pressure is around 90 psi. Boiler capacity is typically around 1.6 litres.

Two non-radiant superheaters are usually used. These do not project into the firebox. Significant improvements in efficiency have been demonstrated by using stainless radiant heaters projecting into the firebox.

The blower is supplied from a hollow stay on the right hand side of the locomotive. Walschaerts valve gear is provided with a screw reverser. A snifting valve is fitted in the lower part of the smokebox.

The regulator is of a conventional screw down type.

Martin Evans suggests that the lubricator is mounted between the frames.

Improvements on the original design

 * Making the superheaters from stainless steel and projecting them into the firebox (making them radiant) shows a significant reduction in steam consumption and the ability to notch-up further.
 * Making the ashpan deeper than the original allows the locomotive to run longer before it requires emptying. Where allowed, this extra depth allows you to leave a small open rear to the lower back edge of the ashpan, allowing a cautious engineer to rake out the ash to allow continuous running.
 * A small hole on the outer face of the expansion links allows for easier lubrication of the die block.

Drawing Errors

 * The running boards are dimensioned as having 1 7/8" total width. This width would not allow the stiffening strip to sit in the cut-out on the motion plates nor would it cover the steam chest fully. It is believed that the correct dimension should be 2 1/32.