paul
Member
Posts: 8
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Post by paul on Mar 21, 2008 20:20:42 GMT
Just about finished the latest 'clapper valve' engine (from Stan Bray's book) a few days back but it doesn't want to run on air or steam (mind you it turns over silky smooth when tweaked!) LOL. I'm sure that it's the design of the valve - a free floating 3mm ball in a 4mm tube is never going to seat correctly of it's own accord IMHO. (On the aquarium pump I could see it flying back down the silicone tube when tweaking the engine!!) I'm going to make a new valve body and fit a spring-loaded valve as per my drawing.... just need to get myself a 2mm die to cut that thread and some wire to make the (close-fitting) spring. For anyone that can't figure out what's going on here the piston has a 1.5mm rod sticking out the back that unseats the ball and admits steam at the end of it's stroke. The steam then vents through the highly sophisticated hole in the top of the cylinder. In the new version the rod will push on the threaded part of the valve to achieve the desired result. Possibly. Oh yeah, I soft-soldered the cylinder to the frame as a matter of expediency  (Please ignore the stock nut holding the rod to the piston-crosshead, I haven't had chance to make one yet)    |
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Post by 02jcole on Mar 21, 2008 20:45:02 GMT
Hello Paul,
Not sure of the design, but did you seat the ball into its face like you do when you are making a check valve for a boiler?
Just a thought.
Regards James.
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Post by baggo on Mar 21, 2008 21:28:12 GMT
Hi Paul,
Just an observation but the hole in the 'valve bit' doesn't look much bigger in diameter than the pin. Is there enough clearance to allow plenty of air/steam flow past the pin once it's opened the valve?
I agree the idea of the ball just floating in the inlet pipe without any means of limiting it's travel seems a bit iffy.
John
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steam4ian
Elder Statesman
One good turn deserves another
Posts: 2,069
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Post by steam4ian on Mar 21, 2008 23:15:40 GMT
G'day Paul
You mentioned an aquarium pump. IMHO you will need more than an aquarium pump to run this engine. Consider the air trapped in the cylinder after the exhaust port closes, compression of this will result in a pressure higher than the aquarium pump.
On McCabe's site he has a "clapper" design which uses a modified Schrager valve. Valves are available from a car tyre shop. This could be worth a try as the valve assemblies are often thrown out when tyres are replaced. You will have to cut the rubber off the body and cut the body down so the spindle can be touched by the piston. See "McCabe's Runner" site
Regards
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paul
Member
Posts: 8
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Post by paul on Mar 22, 2008 7:22:46 GMT
James: Does that translate to "give the ball a whack"? If so, yes I enjoyed that bit John: "Plenty"... er, pass! Seeing as how I'm going to make that hole bigger anyway (or bin that part) it's definitely worth giving that a try before anything else though - cheers  Ian: There was some hint of movement when I connected it to the fledgling boiler so you're probably right. I've looked at McCabes engines before but the bent nail for a valve looked too crude (hehe that's rich coming from me, at least those engines work!). I couldn't face fitting a tyre valve mate, I'd rather go and buy a Mamod....hmmmm.....now there's a thought!! LOL |
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Post by havoc on Mar 22, 2008 9:22:17 GMT
From what I see and read here it looks as if this engine works like the CO2 engines used in free flight model airplanes. With a pip on the piston that opens a ball valve. Correct?
Just to know I have the right idea about this engine.
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paul
Member
Posts: 8
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Post by paul on Mar 22, 2008 9:55:20 GMT
From what I see and read here it looks as if this engine works like the CO2 engines used in free flight model airplanes. With a pip on the piston that opens a ball valve. Correct? Just to know I have the right idea about this engine. Yes but it's a more of a rod than a 'pip' - it projects about 12mm from the piston! |
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Post by baggo on Mar 22, 2008 10:48:50 GMT
Hi Paul,
Could also be a problem with the 'timing' i.e. when the rod actually opens the valve. If it opens too far in advance of TDC it'll try and stop the engine rather than run it. If it only just opens at TDC it will only be open for a very short time. If your using very low pressure air or steam it may not admit sufficient to give much driving force. I would imagine that the CO2 engines run at a very high pressure.
John
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paul
Member
Posts: 8
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Post by paul on Mar 22, 2008 11:51:50 GMT
Hi John, The design calls for about 1mm lift of the ball bearing but I allowed for more as I could always shorten the rod later I'll make up a new valve and then experiment. Thanks for the help as ever! Paul |
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(Please ignore the stock nut holding the rod to the piston-crosshead, I haven't had chance to make one yet)
