Snifter valve in alpha engine

[skunkworks]

I am in the process of building a pressurized alpha style stirling engine. I plan on putting a snifter valve in the cold piston to equalize the pressure between the crank case and the cylinders. My question is this. I was just figuring on using a valve that had very little spring pressure - so if the crank case pressure is just a little bit higher than the cylinders it will bleed air in. does this sound correct? Is there any work developed from the contraction of the gas? I am wondering if the pressure in the cylinders should maybe be a little lower at minimum than the crank case pressure and if so - how you would figure out what that would be. (greater sping pressure holding the valve shut)

thanks for reading my ramblings..
sam

[Ian S C]

Don't think I'v heard of a snifter valve in the piston of a pressurised motor, I,v read of its use in atmospheric motors with mixed success. The nearest i'v had is the use of leather cup seals on cold pistons. One motor has a teflon cup seal, I hav'nt tried, but I suspect it would improove if I removed the cup seal.
I think it would be worth making two pistons, one with, and one without a valve so that a comparasin can be made. Ian S C

[skunkworks]

thanks!

I will probably just experiment with the spring rate to see if there is any change.

sam

[Ian S C]

You proberbly should start with a very light spring, you only just want to close the valve, and have little resistance to it opening. One motor in "Model Engineer" had a valve in the piston that I think was mechanicly opened. I think the motor may have been electricaly heated if that helps in looking for it. I wonder if a bit of shim metal as a reed valve would work, say a bit of .0015" feeler gauge. Ian S C