19: steam piston

Time to turn attention to a different component: the steam piston, or, the thing that makes the train go choo-choo.

A relatively straightforward part to model. Since there are, I think, literally no material available on the make-up of the DLRR #1 piston, I had to rely on more traditional sources.

I assume that DLRR uses a built-up piston, the most common type for the period.

The steam piston is made with several parts: the main body called “spider”, the cover plate or “follower”, and the packing.

The spider is simply a casting with 5 points to mount the cover plate. DLRR may have simplified the design to 4 points, but not knowing this for sure, I just go with the traditional design.

The packing consists of a “T” ring and 2 packing rings fitted on the spider. They are supposed to be cast slightly larger than the piston itself. This way, the packing will fit tight against the inside bore of the cylinder. The following cross section shows how the pieces fit together.

Note the notches around the circumference of the packing rings. This allow the rings to expand with heat. The gaps between parts serve the same purposed.

And here’s the piston as a whole, with transparent cover plate so that the spider can be seen.

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