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When gas expands it gets colder - which chills the container (cylinder) so when using air at room temperature to run an engine the result is that the engine will be chilled and things will get tighter/harder to turn overSo if you want to wear out your steam engine fast - run it on compressed air .Jo
Ok I tried to make it too simple back to the theory....When compressed air expands the only heat it can acquire comes from a fall in its own temperature (which causes a reduction in specific volume) and from the cylinder walls.
Although an engine run on air will cool slightly the difference is generally far less than the heat gain of one run on steam. If we take ambient air temp as 20deg C a steam engine couled get upto over 100deg C during running depending on teh steam pressure and themp but I've yet to see one run on air get below freezing so the amount of contraction is minimal in practice and really not worth worrying about.Also the bearings are usually quite a way from the cylinder so they will get even less of a temp change
Quote from: Jasonb on May 11, 2017, 02:21:05 PMHepolite recommended a difference of 0.05mm per 25mm ( 0.002" per inch ) of bore difference for the gap on their rings between the two applications.Jo