Oscillator Cylinder Pattern

[vtsteam]

Sorry about the 7 bar, yes 3!

After much thought about the effects of steam pressure, I'm thinking about the possibility of forming a steam chest to provide face pressure. This would have a stationary valve disk with stem that the port face bears against and rocks. The valve chest cover would contain the bearing and stuffing box for the stationary valve stem.

I'm even thinking about doing two of these, one on each opposite side of the cylinder. One would be for inlet, the other for exhaust. In my imagination, the inlet valve stem would be hollow and contain a duct. The inlet valve would bear against the cylinder side of its valve chest, while the exhaust valve disk would bear against the steam chest cover which would be faced for that with port. This would require much less spring pressure, as the steam pressure would be self-compensating across the cylinder, and be easier to balance. I believe there would be more flexibility for valve timing with separate valves and configured channels. The steam connections might be axial on the valve stems, but because they are fixed, wouldn't require slip fittings or flexible hoses. Inlet stem would need a radial port into the steam chest.

Somebody must have thought of all this before, but it's new to me just from puzzling over the problem of steam pressure on a large valve face compared to conventional D-valves and valve chests. I'd like to try this, but I'll have to make a new cylinder casting for it, shaped more like a cross than a tee.

For that pattern, I'll add what I've learned on the first one, which will be to split it, and to lengthen the ends to provide chucking pieces. Boring the first one was really difficult to set up on the lathe because it required furniture not to bore into the chuck, but with furniture, the valve body prevented a good grip by the jaws. It took a lot of partial operations from both ends to get enough facing and boring done to trust an indicated surface enough to do a full bore and final facing pair.

I could probably have made up a custom arbor once the bore was through, but I wanted to leave the bore undersized in case of other machining needs until the end, and I I don't like making weird undersize arbors that can't be used for anything else.

But a chucking piece cast in makes everything so much easier, so that's what I'll do -- it will be cored with the bore, I just need a longer core.

I don't know what to do with the present cylinder -- I have a couple of ideas, maybe I will try one. But I'm right now even more interested in a second cylinder per above.

Merry Christmas all. My family and I have had a wonderful morning....!

[vtsteam]

Some valve faces are open-port, and some have cast passages, where only the ports open through the valve face.
Here is an open-port design, and it works fine.
I would guess a closed design would leak a bit less.

At any rate, the force acting on the cylinder/port face would only be generated by the area of the steam ports/passages, which is a small percentage of the entire port face.

I'm not sure I would agree with this unless there was absolutely no leakage across the face.

[Jasonb]

The two trunions in bearing blocks is a good way to get a seal without having to add friction when a post face is held together by spring or screw pressure.

You could also add a flat top to the cylinder pattern and have a regular slide valve, a bit like the "digger" I made a while ago.

[CI]

I'm not sure I would agree with this unless there was absolutely no leakage across the face.

The leakage would complicate things if you consider it.
.

[crueby]

I'm not sure I would agree with this unless there was absolutely no leakage across the face.

The leakage would complicate things if you consider it.
.

However the math works out when leakage, etc is considered, fact is that many oscillators like this have been made with minimal strength springs needed. Even with leakage, that would only effect the whole face if the pressure couldn't get out around the edges of the face, which it easily can. Larger high pressure oscillators used for real work usually bring in the steam through the trunnions they oscillate on, eliminating this issue entirely.

[CI]

There would be a pressure drop across the face (guessing), ending in zero or atmospheric pressure at the outer edge.
You would not develop full force from the steam across the entire pressure drop zone, since the pressure is dropping off.
One way to rationalize it I guess is to operate an oscillator with a spring loaded valve face, and back off the spring tension until the face leaked.
Then tighten the spring until the leakage mostly stopped.
Remove the spring and compress it the same amount, measuring the force required to compress it, and that would be an approximation of the force being exerted on the valve face ?
.

[vtsteam]

Yes, CI, maybe I should just continue with this one as-is and see what happens, then think about my other idea after learning how well this one works. I do have a tendency not to finish projects when I get another idea about how it "should have been" after starting something. This results in a lot of half-built engines. I think at this point I'd rather have a complete engine with whatever problems it might have, than just a bunch of pieces of different ones, none working or proven.)

Let's see what happens with a spring and trunions with this big valve face and maybe 50 pounds of steam. (for that I will need a boiler as well. But no use complicating my thoughts even more -- right?  )

[CI]

I do have a tendency not to finish projects when I get another idea about how it "should have been" after starting something.

Story of my life.

Edit: Sometimes the adage "Less is More" turns out to be true.
.

[vtsteam]

 

But you did that scooter pretty fast, btw.

[CI]

LOL, the clutch is having problems releasing when it gets hot, so back to the drawing board, and total redesign.
I am going all belts and pulleys, with a pulley clutch.
I adjusted the speed a bit slower with the pulley ratio.
I will post some more pictures.
And I did not like the twist throttle; my hand was going numb, so I ordered a thumb throttle.
Relocating the jackshaft higher so the pulleys don't drag on the ground when I turn.
Making a motorized vehicle is tricky.
I am in the refinement stage at the moment.
.

[vtsteam]

I think the refinement stage is kind of a fun place to be. Last year I spent some time refining a hot air engine, and that was very enjoyable, thinking back on it. I might actually like doing that better than building new -- travesty, I know!

[vtsteam]

I had a little time before dinner tonight to sand and paint the cylinder cover patterns. Here they are, showing one assembled and one taken apart, illustrating a pegged "loose piece" pattern. The peg should be a close but loose fit so they come apart with the mold halves when you split it.

Notice that the fillet stays with the longer narrower piece, which will be used as a combination chucking piece and cylinder gland boss.

[CI]

 

[vtsteam]

Thanks CI.

It was too cold to do anything in the shop today, so I spent the time the figuring th engine's stroke, and then the oscillator's pivot angles, finally trying out the port locations and sizes vs. what I have for tooling.

This is what I've finally come up with as the most breathing I can give it with the cylinder dimensions as they stand now.

[Jasonb]

My only thoughts are that as you want it to do work then the holes may be a bit restrictive.

I make the area of the two holes 0.017 square inches.

My 1.375" bore traction engine has an area of 0.047 ( six 3/32 holes), a 1.5" bore Stuart has ports of 0.078", Pat's Green Twin about 0.050" for a 1.25" bore

Could you squeeze a 5/64" hole on the inside or mill a slot rather than holes?