New Compressed Air Hit n Miss Engine

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NickG:
Chuck,

thanks for explaining the valve mechanism clearly. What sort of pressure do you think this would work down to? I can see that it's partly due to the strength of the spring on the ball and I realise that you want it to behave as much like an i.c. engine as possible hence the high pressure but was just wondering. I guess it wouldn't sound much like an i.c. at the lower pressures but should still work? It won't take much pressure to lift the valve off its seat. I initially thought by looking at your cam you were getting the pressure to act in a short sharp burst but looking again it looks like the valve can be open for about 90 deg on the cam? = a full stroke? I guess you could play tunes with that too but the way you have it will give the most power.

Anyway, brilliant stuff :thumbup:

Nick

cfellows:

--- Quote from: NickG on May 22, 2011, 07:02:35 AM ---Chuck,

thanks for explaining the valve mechanism clearly. What sort of pressure do you think this would work down to? I can see that it's partly due to the strength of the spring on the ball and I realise that you want it to behave as much like an i.c. engine as possible hence the high pressure but was just wondering. I guess it wouldn't sound much like an i.c. at the lower pressures but should still work? It won't take much pressure to lift the valve off its seat. I initially thought by looking at your cam you were getting the pressure to act in a short sharp burst but looking again it looks like the valve can be open for about 90 deg on the cam? = a full stroke? I guess you could play tunes with that too but the way you have it will give the most power.

Anyway, brilliant stuff :thumbup:

Nick

--- End quote ---

Hey Nick, thanks for the input. There are a number of variables that determine how these air engines operate. I'm in new territory with this quick release inlet valve but I do have some experience now with the ball slave valve. With a lighter spring, the engines will run on lower pressure but they won't rev as high. Most of my engines are slow runners and I use a light duty spring, about 5/32" OD, 3/4" long, wire size of .012" - .015". They will run well on about 40 PSI, maybe less.

For this engine to sound as realistic as possible, I want it to free-wheel for as many revs as possible, then hit really hard when it fires. The idea is to control the speed with the governor, not the air pressure.

I finished up the valve last night to a point where I could test it. With the valve closed, there was no leakage, and the air pressed hard on the valve stem. However, I was able to hold it with my thumb and forefinger. I think this valve is going to work well, although I might have to rebuild the valve body for a smaller, 3/16" valve stem... 1/4" may exert too much pressure on the cam assembly.

Chuck

cfellows:
I'm into the fiddley bits now so progress will probably be slower and not very exciting. I had decided to use 3-48 SHCS to fasten the two halves of the valve body assembly to the base. However, after I drilled and tapped the holes, I found that my screws were too short. So, I made some brass screws from a piece of hex rod I had on hand. Screws turned out nice:

But, when I tried to tighten them down, I promptly twisted one off. Guess brass was a bad idea in these small sizes. So I drilled out the holes and tapped them to 4-40. Had the right size screws on hand and screwed the valve assembly to the base:

Next I started on the timing gears. The small gear is made from two pieces, the gear and the hub. After the gear teeth are cut, the gear will be bored out, then loctited or hard soldered to the hub / collar. Here I've turned the gear blank and the hub at the same time from a piece of 1" 12L14.

Next I'm parting off the hub:

Here's a picture of all the gear blanks. The large timing gear was turned from cast iron and will have a pitch diameter of 1.5". The small gear is mounted on a mandrel, ready to have the teeth cut:

Today's work will include cutting the teeth on the gears and getting the smaller, primary gear assembled into one piece. Then, it's on to the cam.

Chuck

cfellows:
Here's a couple of pictures of the gears. The first picture shows the primary gear set before assembly.

And here's a picture showing the large timing gear and 2 copies of the small timing gear with hub. The one on the left shows a pitiful attempt at silver soldering. I used too much solder and got the assembly too hot. This resulted in solder flowing into the valleys between the teeth. I tried to dig the solder out but no luck. Now I know why they call it hard solder! The assembly to the right is put together with loctite 620. It will probably hold alright... at least I've not had it fail on any of my applications yet.

Chuck

cfellows:
One last picture for today. Got the cam finished and attached to the large timing gear.

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