8 x 10 Atlas

We got our first steam engine today. It is a 8 x 10 Atlas. Don't know much about steam engines, but it seems to be in good shape. My question is what HP is it? and are there any pictures of this engine around ? I need to know if all of it is there and what color it was. Thanks Kenny

Hi Kenny!

The formula for steam engine horsepower "by the numbers" is as follows: PxLxAxN/33000, where P=mean effective pressure, L=length of piston travel ( in feet ) per revolution, A=area pf piston ( in square inches ), N=number of revolutions per minute.

As you can see, you will have to make a couple of assumptions. A is easy, on an 8" piston it's 18.8 sq. in.. L will equal 20" ( for 1 revolution ) / 12 to get it in feet, or 1.66'. You may be able to figure rpm from the governor markings, if any, but for the sake of example let's assume 150 rpm. Now for the tough one, P. The mean effective pressure is not the pressure at the throttle valve, but rather the average pressure in the cylinder from admission to release. Since the "intake" phase only occurs for a portion of the stroke, and the steam pressure in the cylinder drops from there to the release point as the steam works expansively, it will only be a fraction of the pressure at the throttle. Let us assume 70 lbs. per square inch based on a throttle pressure of 110 lbs / sq. in., and that's a rough guess. That gives 70 x 1.66 x 18.8 x 150 = 327684 foot pounds, divided by 33,000, the number of foot pounds per horsepower. The result is 9.9 or roughly 10 horsepower, which would be appropriate for engines built in the 1880's. A few years later that M.E.P. might be closer to 95psi, rpm closer to 200, and the horsepower closer to 20. As for the color, that could be anything. I have a 10" x 12" that had three coats of red, one of gray, one of black, and a very nice Hunter green next to the iron. I don't know who made it, but I'm going to paint it green. Hope this helps. JM