Bob Jorgensen's hand-build Dake Square Piston Rotary Steam Engine.
See all of Bob Jorgensen's steam engines at his web page
https://sites.google.com/site/jorgensensteamsite2/
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CLASSIC STEAM ENGINE ENGINEERING FORUM
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The Dake steam engine uses two square pistons.
One piston looks like a slice of bread, and it operates inside of another piston that looks like the crust from a slice of bread. The inner piston moves up and down only inside of the larger outer piston. The outer piston moves side-to-side only inside of a flat rectangular chamber.
The inner piston has a hole in the center, and the crank pin extends through this hole.
The crankshaft is a simple disk on a shaft, with a single crank pin.
The engine operates when steam is admitted to the outside of either side of the large piston, moving it from side to side. When the large piston moves from side to side, it also moves the inner piston.
Steam is also admitted to the top and bottom sides of the inner piston, causing it to go up and down inside of the rectangular outer piston.
Valving is via four ports in the hollow inner piston, which lead to the outside of each side of the large piston, and ports which lead to the top and bottom of the inner piston.
The steam enters the engine through the pipe fitting at the top, and then through a slot in the back housing, and goes to a circular ring in the back plate of the engine. The exhaust goes out a center hole in the back plate, and then up and out the brass fitting on the top right of the engine. The engine crankcase is made of three plates of steel bolted together. The center plate is hollow to allow room for the pistons.
The engine has no dead centers, since it is basically has two-pistons acting in a common flat rectangular cylinder. It is equivalent to a two cylinder steam engine, but is really a two-piston, one-cylinder engine.
If you understand how a Scottish Yoke works, the large Dake piston is like the yoke, and it is pushed side-to-side in a rectangular chamber by steam admitted to either side of the outside of the large piston. The small Dake piston rides inside of the yoke slot, moving up and down in the slot, similar to the way the guide shoe in a Stepherson's link works.
The valving could have been designed external, but was instead included as part of the inner piston, so the valving works similar to an oscillating steam engine, with four ports. The engine can be reversed even at full speed, and the reverse valve located in the round chamber at the top simply reverses the steam and exhaust passages in the round chamber at the top of the engine.
The best way to understand the engine (and for me the only way to understand it) is to partially disassemble it, and observe the pistons moving. I will add a video of that soon so it will be clear how it all works. A picture (or video) is worth a thousand words.
It appears that the engine produces nearly even torque as it rotates, and power is generated in all four quadrants of the crankshaft movement.
The inner pistons must be fitted carefully to the cylinder chamber to prevent steam and exhaust from escaping around the faces of the pistons. The front plate must be carefully machined and gasketed to give the correct clearance.
The engine runs with almost no vibration, since it does not have the reciprocating mass of the piston rod, crosshead, or connecting rod.
There is a single gland where the crankshaft exits the right side of the engine. The end of the crankshaft inside of the engine is not supported.
Apparently a similar design by Roots was patented earlier, but it is not apparent in the Roots patent how all the valving worked. The Dake appears to be unique in that the steam valving and ports are built into the inner piston, thus eliminating the need for external slide or piston valves.
The Dake engine was a commercially viable engine, and was used in many applications such as a steam ship steering motor, ship anchor hoist, forklift motor, mine pump motor, and many other applications that required a very compact and totally enclosed engine design.
The outer piston moves side-to-side only, and the inner piston moves up and down only, but since the inner piston is moving within the outer piston, its ultimate movement is circular. I am not sure if the engine qualifies as a rotary engine, since each individual piston motion is linear only.
Charles Dockstader has an excellent simulation of the Dake interior engine parts running. You can do an online search for Charles Dockstader and download his Dake simulation program. Charles is the master of steam engine valve gear simulation programs.
The steam ports extent to either side of the inner piston, and are then elongated, so that steam can also pass through the holes in the sides of the outer piston, even when the inner piston moves up and down.
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Thanks.
The Dake is a very smooth running engine due to its design.
It surprised me when I first ran it.
steamnut2008 2 years ago