There is a steel ball in what looks like a chimney on my Poppin engine, this was not on the plans and added by me, it is a self made ball check valve of sorts that improves the efficiency of the engine, these type engines often employ a slide valve and slide valves can leak if not really well executed, this is one of the reasons flame lickers can be troublesome to tune. What happens is slide valve goes open and piston travels towards bottom dead center and draws in hot air then slide valve closes and air is cooled and makes vacuum to suck piston towards top dead center...if slide valve is nearly perfect seal this can be a fairly strong power stroke...however...what happens in real life is often the slide valve leaks badly and the engine will not run..if it leaks only a little the engine will run but not make much power...in this comon situation as the piston nears top dead center it should still be under vacuum or negative pressure but it is all to common that the last roughly 1/3 of the up "power" stroke the piston is actually making a little compression or positive pressure! (slide valve leaks for the entire time it's closed)This is very bad as it is trying to stop the engine from running rather than making power...the engine "can" sometimes still run in this bad condition if the power stroke was strong enough to get the flywheel moving fast enough to get the piston pushed thru to the nest cycle...enter the ball valve fix!...on the down stroke the ball is sucked down to a tapered hole to make seal and engine is happy...then on the up stroke as the air starts to turn from negative to positive pressure near top of stroke the ball is not heavy so the ball is blown up and the positive pressure is vented so as not to hamper piston power stroke. This simple system is said to improve power by approx 1/3 or in the case of a badly leaking valve it can turn a non running engine into a running engine.
Some might view it as a band-aid as the real problem is a leaky slide valve.
I view it as it adds visual intrest to the engine! It is also fun to look in the stack and watch the ball jumping up and down...it sounds like I am popping popcorn made from ball bearings.
Normally there is a threaded screw mounted above the ball to control how high the ball jumps...this is to tune for best running. It is important for the ball to jump quickly to let the positive pressure out...but equally important to get the ball back down quickly to seal for the next cycle.
I tried a threaded screw but it killed the smoke stack look so I came up with the little metal screen over the top...looks neat and offers a cushion stop for the ball and much more quiet popcorn sound.
This got to be long...hope I did not put the experienced guys to sleep or worse yet make them mad.
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