Author Topic: Pin valve air engine (inspired by Chuck Fellows)  (Read 7317 times)

Offline BillTodd

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Re: Pin valve air engine (inspired by Chuck Fellows)
« Reply #15 on: June 02, 2015, 03:07:33 PM »
There seems to be a couple of designs of these palm nailer, one of them is a proper impact device and has the plunger and piston shaped to take the blow. The one Chuck has drawn is only designed to thrust the nails in using air, it , might be a better choice for a hit-n-miss :-)

I had another (better)  idea for the pin valve  engine , that uses a second pin and spring in the head to maintain the open air port until cut-off by a variable spring force i.e. it'll cut-off when the air pressure in the head drops as the piston accelerates (much like Chuck has been noodling of late)

Offline cfellows

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Re: Pin valve air engine (inspired by Chuck Fellows)
« Reply #16 on: June 02, 2015, 04:51:41 PM »
I lay in bed thinking last night what a perfect driving force one of those "impact" type cylinders would be for a hit and miss engine. After it fired and the flywheel went into "high revolution speed" mode, the lockout lever would simply interrupt the air supply to the cylinder. While the engine coasted (the miss part of the cycle), the air chamber would have time to recharge. When the flywheel slowed down enough, the governor weights would let the lockout lever return to it's normal position and let air flow resume, and the "hit" cycle would repeat. The air chamber requires a bit of time to recharge with air between shots , and the miss cycle of the engines would give it that required time.

The Palm nailer would be ideal for an air engine, even one that fired continuously.  Its recharge rate is very fast and it hits with surprising force.  Unfortunately, it's kind of complex and requires pretty tight tolerances on the parts.  A multiple cylinder engine requiring this assembly for each cylinder would quickly get pretty complicated, not to mention the design challenges of keeping it looking like a real engine.

Bill, to your points on the pin valve, I would like to keep the design as simple as possible and the parts count to a minimum.  This is particularly important for multiple cylinder engines.  I like your ideas and hope you aren't discouraged by my list of evolving requirements.  The more ideas we have, the better our chances of developing a new design.

Chuck
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Offline cfellows

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Re: Pin valve air engine (inspired by Chuck Fellows)
« Reply #17 on: June 02, 2015, 05:16:28 PM »
Here is an alternative to the pin valve arrangement that uses a small vertical slot in the side of the piston to uncover ports in the cylinder wall at near top dead center until slightly after TDC.  Timing should be similar to the pin valve arrangement in operation.  Thoughts?

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Offline tvoght

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Re: Pin valve air engine (inspired by Chuck Fellows)
« Reply #18 on: June 02, 2015, 11:27:38 PM »
When I was a kid, we had a book around the house called The How and Why of Mechanical Movements. I believe it was published by Popular Science magazine. I looked at it for hours and hours, and took a lot of inspiration from it.

Anyway, the book described a couple of what were called "automatic engines". One was the bump or bash valve type used in CO2 airplane engines (similar at least on the inlet side to what's being discussed here). The other I thought was simpler, and as a kid fantasized about building one.

The attached picture shows  it schematically. The piston (in red) had a deep depression that was filled by a long projecting head (blue) at top dead center, where the inlet port in the piston aligned with the inlet port in the cylinder. Near bottom dead center, the piston port aligned with the exhaust port, while the inlet was covered by the piston.

--Tim

Offline cfellows

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Re: Pin valve air engine (inspired by Chuck Fellows)
« Reply #19 on: June 03, 2015, 05:44:57 AM »
Thats an interesting design, simpler than mine.  The only issue I see is trying to incorporate the slave ball valve for the exhaust.  A slight variation would be to make the inside piston walls and the head protrusion straight, then drill a small hole down from the top of the piston to connect with the hole coming in the side of the piston.  Might even be worth adding an o-ring between the head protrusion and the inside wall of the piston to make it air tight.  Still don't quite see how a slave exhaust valve could be implemented.

Another source of inspiration is high pressure airguns.  These include pellet guns as well as paintball guns.  Due to the popularity of paint ball, there are a lot more commercial designs out there, although most of them are quite complex and include automatic reload and cocking.  Still, here is a relatively simple valve I found that looks like it might have possibilities.



It's similar in principle to the one you uploaded, Tim.
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