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?Chinese? Stirling Beam Engine
NickG:
Peter,
It sounds like the displacer is catching the hot cap to me when it's hot. What is the clearance like between the displacer and and hot cap? Mine has about 1/32" all around.
Another test, when everything is sealed up, as you turn the flywheel and the power piston is travelling towards the top of its stroke you should feel slight suction. Likewise, as it travels towards the bottom of it's stroke you should feel slight compression. If not there may be a leak in the system, as you've tested the rest, it points towards the fit of the power piston in it's cylinder. It may be too loose? I know it's a pain but you could try the 'pop' test. You would have to strip it back down, cover the displacer rod gland hole and the hot cap end and pull the piston out to see if it pops which tells you it's a good fit.
Other than this, I'm at a loss! :scratch:
How much of a leak was there around the displacer rod? Should only be a few small bubbles, you should still be able to build up a reasonable pressure in there.
Nick
sbwhart:
Peter
Nick made a good point regarding the displacer catching when hot this could explain it running freely when cold but problems when hot there could not be enough clearance to allow for thermal expansion.
Good Luck
Stew
klank:
John, Nick, Stew - thankyou all for the advice.
I turned it over super slowly when hot - no feel of binding or bottoming out anywhere.
I get loads of suck n blow from the top of the power cyl - with or without heat. - I put a little piece of cling film over it, held by an O ring. See it move in and out as it should.
Maybe I have too generous a clearance at the end of the hot end for the displacer piston - mine is over a 1/4" at the full extent of its stroke?
When I did the water test, there was a steady stream of quite small bubbles from the displacer rod bushing - ?possibly too much? - the rod moves freely, but with no slop.
Anyway, I have put the beast on a shelf to leer at me whilst I try and finish another project - to motorise the X axis of my Sieg X2 mill - lots of good stuff here about that.
Maybe I should post some pics/dimensions? - done mine with a wwm - but no need for complex clutch/linkeage.
With much respects and best wishes
Peter
Darren:
--- Quote from: klank on May 14, 2009, 11:55:50 AM ---whilst I try and finish another project - to motorise the X axis of my Sieg X2 mill - lots of good stuff here about that.
Maybe I should post some pics/dimensions? - done mine with a wwm - but no need for complex clutch/linkeage.
With much respects and best wishes
Peter
--- End quote ---
Maybe you should, :worthless:
NickG:
Peter,
Sounds like you could be homing in on the issue with the stirling. 1/4" is much too big a clearance, mine is 1/32" at each end, the same as the radial clearance. Because of the 1/4" gap, you aren't efficiently displacing the air from the hot to the cold end ... even when the displacer piston is right in the hot end, there is still that volume of air being heated, counter acting the effect of the cooling on the other portion of air.
From everything else you've said, it should work once you get the clearances right on the displacer ... easiest way is to make a longer one and bigger diameter if that clearance is too large. The only thing you have to be wary of is making it too close a fit, then it can cause sort of viscous drag as the air has to get down the sides!
Nick
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