I wish to document and build a 1-hp model of a one-cylinder engine artifact currently in Stehekin, Washington.

The prototype engine stroke measured about 13 in. That would be unlucky, however, so I am going to assume it was 12 in. and I didn't allow for the thickness of the piston. So I will use 9 in. bore x 12 in. stroke. So that means the stroke is 1.333 x bore. For a 1-hp engine running at 4 strokes/sec (120 rpm double-acting) with a M.E.P of 50 psi we have:

550 ft-lb/sec = (4/sec)* (stroke in inches /12) * pi * (bore inches/2)^2 * 50.

i.e. 31.5 = b^3 or bore = 3.158 inches x stroke = 4.210 inches.

This is a scale factor of 1:2.85

The boiler is a 1947 lap-seam miniature code boiler.

Here is a thumbnail of an intact Atlas Engine in Eureka Springs, thanks to J. James Miche

Here is his photo log.

I also recently purchased a pop valve off of eBay for $31. It is new, 3/4" NPT and is set to 100 psi.

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© 2008 Charles Turner