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)
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.
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
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
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.