October, 2007.

John R. Bentley 2007.

Notes on the Model ∆olipile
From the design of the World's First Rotating Steam Engine


If you build a working version of an Aeolipile, ensure that YOU are satisfied that it is safe to operate.
This is an adaptation of a 2000-year-old design.  Before firing up be prepared to assume all the responsibility!

The following is simply information about how I constructed my own model.
It is not intended to be a set of instructions for building a similar version.

Although it's not necessary for the sphere to be hollow, mine was constructed from two thick brass ringer gongs taken from inside a dial-type desk telephone from the late 60's.  They were not true hemispheres, so I heated them red hot with a propane torch to anneal them, then pounded the heck out of them until they looked like half golf balls (with the dimples).  I silver-brazed the two halves together at their peripheries, then polished them in the lathe.  Easy-flo 45 silver-solder is great since it takes some copper from the brass and when polished, it takes on the host color and the join is unnoticeable.  The sphere is 2" diameter.  I made no attempt to turn the sphere to an accurate shape, rather I elected to simply file it smooth and polish.  Perhaps this lends a hint of the ancient origins of the Aeolipile.  The "nozzles" are very short pieces of 1/16" diameter brass tubing soldered into the ends of the 1/8" lengths of copper tubing that makes up the nozzle arms.  The orifice size is about 1/32".

The cauldron is an ordinary 6" stainless steel mixing bowl from a "Dollar store".  It had a flat bottom, so I pounded it out to round (not necessary) - and that took all afternoon.  The cover is composed of two copper disks, sandwiched together for strength, but I'm sure a single thicker plate would have been fine.  Putting a flat top on any pressure vessel isn't too smart from a safety standpoint, so I hid a piece of stainless steel angle stock inside & fastened it to the two 5/16" dia. copper supporting arms and to the top cover for rigidity.  A large 1/2" diameter brass stay is connected between the bottom of the bowl and this angle piece to hold everything together.  A bead of GE Silicone II seals the rim.  (I don't know if Heron of Alexandria used that stuff or not)

There is a filler cap on the top cover made from solid brass which sits on the hole and acts as a safety valve weight, holding the pressure to 1.8 psi.  The weight has a small peg on the bottom which protrudes into the hole to keep it aligned. The peg has flats along its sides to allow steam to pass, thereby preventing it from acting like a piston and launching the safety valve weight clear of the engine altogether.

The stand and legs are made from strips of mild steel silver-brazed into position.  The cauldron simply rests in the ring at the top of the frame.  The black finish was produced by heating the assembly with a small propane torch.  I felt this type of construction and finish was in keeping with the rest of the model's exterior, avoiding obvious screw heads and other modern finishes such as paints and lacquers.

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© John R. Bentley 2007.