The Power Piston                                                                                  

Christmas chaos is finally over and the weather has warmed enough to start working on the heat engine project again. 

I made a major progress on the power piston design. 

 I had been planning on making a rolled cloth piston seal by sewing together the ends of a yard long  strip of raincoat material to make a closed loop.  One edge of the loop would be attached to the piston (green) and the other edge would be attached to the slightly larger diameter cylinder (blue). As the piston moved in the cylinder, the excess cloth (red) would have rolled above or below in the gap between the moving parts. The cloth seal would have had to be hand sewn, would probably leak, would have a short lifetime and be difficult to replace.

Instead, I made the piston seal from a $4.99 twelve inch bicycle inner tube. The cylinder is made from trimmed down 3 ½ gallon HDPE paint buckets. The piston is made from slightly smaller paint buckets. I put paired conical bucket pieces together such that the piston (green) has a slight hour glass shape and the cylinder (blue) has a slight barrel shape. This makes the gap between the cylinder and piston like the space between the symbols <>. The inner tube (black) is inflated in the space between the piston and cylinder walls and fits into the widest part of the gap like this <0>. As the piston moves in and out, the inner tube rolls minimally in the gap and is self-centering to a mid-stroke position. The piston face has 95 sq. inches of area so 1 PSI of pressure difference will produce 95 pounds of force. Stoke lengths are at least 0.75 inch from center, both outward with positive pressure and inward with negative pressure, for a combined piston travel distance of at least 1.5 inches. The piston was easy to make, it is robust in design and it does not leak. The year is off to a good start.