Oscillating Engine Valve Gear Query

I have come across an old etching of an oscillating engine that looks like it would be a nice project to make.

You can hopefully see in the above that it has a slide valve that is opperated by a rocker arm pivoted off the side of the cylinder with the other end running in a grooved "channel" that I believe can be moved to reverse the engine.

Before I spend some time trying to work out the exact geometry of the linkages I was woondering if anyone had a drawing of this type of valve gear in an old book of knew of an engine fitted with it. Unlike a lot of oscillating engines this one does not have an eccentric to move the valve like you find on say Penn's valve gear.

Thanks, Jason

That looks very like a Hackworth type set-up. The roller in the end of the valve lever would engage the channel located above the bearing/trunion.

It would make a great model!!

Pete

Thanks Peter. The Hackworth gear does indeed look like it has a similar channel which lets the valve lead the crank depending on what angle the channel is at. Just need to work out the geometry that will move the valve rod in using the cylinders movement rather than the link from the crank that the Hackworth uses.

I too think it sould make a nice model, The old advert says the engine came in 4", 6" and 8" bores, it does not help that the bricks on the wall vary in length but I think I will assume that the 6" is illustrated so at 1/4 scale that would give me a 1.5" bore x 3" stroke which my compressor can just about keep up with. The flywheel will also be an easy job cut from the solid.

Watch this space

J

PS While I'm here I seem to remember the SMEE having an old oscillating wall engine that they have on their stand at some shows, does anyone have a photo of it?

Edited By JasonB on 01/08/2016 14:54:59

Looks like Elmers No 42 may hold the missing link

Edited By JasonB on 01/08/2016 15:22:04

I'm a bit confused by the illustration as it shows the 'roller' not engaged in the 'slot'. I don't see any mechanism for moving the 'slot' over to the 'roller' either. ??????

Pete

I think what you are saying is the roller is actually the nut holding the rocker arm onto the cylinder, the arm carries on towards the wall which would place the roller towards the rear of the slot.

I can't blow the image up much more without it pixellating.

Edited By JasonB on 01/08/2016 18:34:24

If you can figure out taht one, you should draw up plans and send it to Diane!

The Flywheel will suit fabrication, I like the balancing pockets!

Some interesting challenges in making the 'forged' crankshaft and in making steam-tight pivots, but the steam passages should all be possible to do as straight lines.

Neil

Jason,

Got it! I couldn't get an enlargement like you have. I agree with your assessment, especially since it puts the roller back in line with the trunions on the cylinder. That bothered me also.

I'm adding this engine to my build list (which is too long!). While castings would be really nice, bar stock will do a good job also.

Neil, I'm pretty sure how i would do the crank. A bit fiddly but.....

Fascinating engine!!

Pete

You could go teh forging and bending from solid route but it would need a good heat source to form tight bends. Or the other opttion is to just machine it as you would a solid crank and rather than leave the webs rectangular section shape then so the are round, this could be done with a roundover bit followed by files.

A third option would be that I design it to use a SG iron cast crank from something else like this one one of mine.

I suspect there is something missing from the engraving. If the curved slide thing was mounted in slides so that an eccentric on the crankshaft caused it to move up and down vertically, then it would operate the valve, and compensate for the waggling of the cylinder. Not perfectly, but on a simple thing like this you'd get away with it

Duncan, there are several designs that use an eccentric such as Penn's which I mentioned earlier. But this one does not use an eccentric there are a few ways these were arranged, in this case there is a STRAIGHT channel much like on Joy or Hackworth valve gear but the rocking motion of the valve chest provides the main source of movement not an eccentric.

The only thing I can't see is an actual reversing lever for the operator to select direction.

This is one example without an eccentric but as the pivot is fixed off to one side of the pivot point the engine can't be reversed, also better suited to end pivoting rather than middle. Valve gear closeup at about 1min in.

And this is Elmers No 42 which is close to whats needed but not reversible

Edited By JasonB on 02/08/2016 07:44:09

> The only thing I can't see is an actual reversing lever for the operator to select direction.

It may be for driving line shafting, perhaps you just angle the channel to give the direction you want, bolt it up and leave it.

Neil

As requested, some pics of the SMEE model wall engine:

Thank you very much Gwil. It is even closer to the engraving than I remembered. Almost certainly based on the same engraving as that is dated 1876, the same as the lable on the model.

I have also been given a lead that Anthony Mount mad something similar but as it was not a good runner he only wrote a single article so I'll be searching for that later.

Edited By JasonB on 03/08/2016 14:53:39

I suspect that this is how it was done. Adding a lever would be easy though.

Pete

That's a beautiful model and it looks to have been run a fair bit. Nice.

Pete

If the only thing that moved the valve is a roller travelling in a curved slot, then the valve motion will be 90 degrees out of phase with the piston motion, so it will work with zero lap and 100% admission. If lap is applied the valve won't open until after top centre, which would make it more than a bit sluggish.

Rummaging about in my computer I found another shot I'd taken (not that it adds a great deal, but here it is anyway) -

Edited By Gwil on 03/08/2016 17:09:17

As I said earlier the roller is in a straight slot that is set at an angle. By altering the angle of the slot you can set the valve to lead the crank in either direction and therefore reverse the engine, the steeper the slot the more lead the valve has. Have a look on you-tube for some examples of hackworth or Joy valve gear to see how the straight slot works. The only difgference here is how the movement is generated.

From having seen that SMEE one running at the shows I would say it's a good runner.

J

PS Thanks for the extra photo Gwil.

Should have spotted straight slide, but no matter what angle the slide is set to the valve is at its mid travel when the cylinder is vertical (it must be for symmetry), and at its max travel when the cylinder is at max inclination (approx half stroke) so altering the angle only changes the magnitude of the valve travel, not the angle of advance. This is not the same as Hackworth/Joy which add a variable out phase component to a fixed amplitude in phase component to achieve variable angle of advance. Yes setting the slide the opposite slope will reverse the engine. 

Edited By duncan webster on 03/08/2016 23:16:02

Edited By duncan webster on 03/08/2016 23:16:58