Diagam of sealed piston with pictures

Here is a diagram of the sealed piston that I am planning to use for the Stirling engine. I have exaggerated the gap to make drawing the bag easier. The kink in it on top of the piston is suppose to be the heat sealed end of the bag. A metal cap will be fitted over the cavity of the piston to hold it in place with a screw.


























The area will be pressured with a working gas, most likely methane, so the bag will be tightly pressed against the cylinder and piston, so in those areas it will not feel the pressure. Only where the bag makes the U turn, will it have to support the pressure of the gas in the cylinder. With a small gap, the force on membrane will be on the order of 1/10th the tensile strength of the material.

Here are some pictures of my tests on the sealed piston.

Piston at bottom of cylinder. The plastic bag is tucked into the top of the piston, but not completely. Then it goes down 1/3 of the length and goes back up to the top of the cylinder.
It is under ~10 psi pressure.


As the piston is pushed into the cylinder, the bag's U-turn moves further down the piston.

Piston at top of cylinder. Note: bag should not extend past the end of the piston.