Rider-Ericsson Hot Air Engine

The very first hobby-related book I purchased was Steam and Stirling: Engines You Can Build. Gracing its dust jacket is one of the most beautiful of all hot air engines, the Rider-Ericsson pump. I knew right off that I wanted to build one, some day. My dream started its way into reality in January of 2010. I tackled the set of castings that I purchased from Myers' Model Engine Works.

Then, spring yard work and other chores kept me out of the shop for three months. But, by pushing myself I got it to run the first time on August's Friday the thirteenth. It was my lucky day!

It took another month of of detail work and painting to get it ready for its very first appearance at Oregon GEARS (Gas Engine and Reproduction Show) in Portland. It performed flawlessly all weekend. It is a delight to watch it run.

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It is finished!

Typically, the original engines pumped water from wells into elevated storage tanks. Along the way the water flows through the upper half of the engine, keeping it cool.

For show-and-tell purposes, the pump takes water from the brass tank on the right, pushes it through the water jacket, and returns it to the tank.

The black enclosure houses the furnace section. It could use almost any type of fuel to heat the "hot cap." Hot air engines need a cold section and a hot section.


This closer look shows the brass water pump mounted on the water jacket. The upside-down "teardrops" are hollow surge chambers. The air inside provides a cushion that evens out the water flow and prevents "water hammer."

The upside-down "U" rods operate the displacer piston. The displacer pushes air back and forth inside the engine, alternately moving it between the hot and cold sections. This results in cycles of expansion and contraction of the air, inside. These pressure changes act upon a power piston which connects to a crank that turns the flywheel. In a nutshell, that is what makes a hot air engine run.


Here is a closer look at the top end. The small brass cup is used to add water to the pump when starting it for the first time. This is known as "priming" the pump. The little valve between the cup and the pump actually works.


Here is a closer look at the priming cup and the "plug valve"


Many people ask whether this sort of thing starts out as a kit of parts that need only be assembled. Far from it! This project started with several raw castings, just as they were when broken out of the sand molds at the foundry. Along with them, the supplier provided a number of "bar stock" items, such as tubing of various sizes. Everything required many hours of precision machining on lathe and milling machine.

On this Web page is a photograph of the "kit," as purchased:
Myers' 2-inch bore Rider-Ericsson

The Ericsson (as it is sometimes called) was a very satisfying project. I highly recommend this Myers kit. The castings were of good quality and the drawings were excellent. I didn't find any errors.


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Revised -- 9/29/2010