Steam Engine Valve Gear driven by Steam Pressure?

pictures?

Rich

I'm no expert on steam, but I get the strongest feeling that there is SUPPOSED to be a link to that shaft on the steam chest. Is there anyplace on the flywheel or the crosshead that the valve could be linked to? Is there anyplace on the mounting board where something else once went, like the reversing gear?

Jon

I have to agree. Your angles for your photos make it more difficult to determine whether there is an eccentric on the flywheel shaft -- perhaps between the flywheel and the crankpin.

It *looks* as though the shaft in the steam chest needs to move the opposite direction of the piston in the main cylinder to switch steam to the proper place. But what appears to be missing is anything to accomplish this.

You could experiment with powering it from compressed air as being a little less likely to cause serious problems than steam would be. I'll bet that as it sits, it will rotate to TDC or BDC and stay there, unless you flip the valve in the steam chest at just the right time.

It just might be that there is some way that the main piston valves steam to a smaller piston in the steam chest to shift the valve.

The best thing would be to find what model this was -- perhaps find it in an *old* issue of Model Engineer (in the UK), to find out what it was supposed to look like when complete.

But it *might* have been a patent model, which means that finding the right patent to examine would be the only real solution.

Good Luck, DoN.

"DoN. Nichols" wrote: (clip) But it *might* have been a patent model, which means that finding the right patent to examine would be the only real solution. ^^^^^^^^^^^^^^^^^ This engine may be a hand-built that was never finished. You may have to invent the missing linkage. I would look at other engines to see how it is usually done.

Isn't there a steam newsgroup?

Is the shaft that appears to be attached to the valve spring-loaded? Is it a single shaft or two that stick out opposite each other? I assume there's no internal linkage or you'd have turned the flywheel and seen movement at the valve chest..

I wonder about the fact that steam can't be gotten to both ends of the cylinder (assuming double-double acting) I see what looks like a tube going to the head opposite the shaft, but it's quite small to be feeding steam to that end of the cylinder. Is that a tube connected to the center of the head and the flange? If so, I could see that having something to do with working the valve.

I can imagine a couple of methods of valving an engine like this with no linkage, but they wouldn't be very ideal..

As Jon says, it could be missing valve gear, but I just don't see any room on the crank for it, unless the counterweight worked as a cam, but I just don't see that happening..

Regardless, you've got a nice little engine and I'll bet someone here is going to know what the score is.

John

This link shows how the linkage in a locomotive works. At the bottom of the page are links to animations.

I would look at other engines to see how it is usually done.

You can do a valve gear system by having the piston move the valve gear back and forth. This will make an engine which is rather wasteful of steam but it will work. The piston approaches the end of it's stroke and hits a pin that moves the valve from the position where the steam is entering one side of the cylinder to the other side of the cylinder. Inertia and the steam pressure on the bottom side of the piston allows the piston to top out on the stroke and start back with the pressure now on the topside of the piston while the bottom side of the piston is vented to the air. That system doesn't make use of the expansion properties of the steam but it does work and requires no valve gear beyond what is in the piston head stuff. I'll also note that steam passages from the cylinder to the valve can also do the movement of the valve.

-- Why isn't there an Ozone Hole at the NORTH Pole?

As far as I can see on the pictures, there is nothing that could be used to fasten some kind of rod to that shaft (hole, thread, whatever)? Right?

Nick

Right. I remember seeing an article in one of the model magazines about an engine that used the steam pressure to operate the valve, but I can't remember where.

wrb

I think it must have originally been designed to have some sort of drive to the valve gear other than steam. No one smart enough to design an engine, would be dumb enough to bring the shafts through the end covers of the steam chest if they didn't have to. Gland are a never ending source of annoyance,so if you didn't need them , why make them?

It's getting stranger. I took the outboard head off - it has a tube in the center that goes through a hole in the middle of the piston - apparently to feed pressure/vacuum from the cylinder at the inboard side of the piston. This is fed out through the top of the head and back into the valve block.

The "shafts" protruding from fore and aft on the valve block are actually just pins. The butt against the top of a valve, allowing it to be pushed in with the pin.

I *know* I've read about this recently, I just can't remember where!

wrb

Good. How long is the tube? Does it reach well past halfway tothe other end of the cylinder? If so, I got some ideas.. If not, I still don't know;-)

John

Somehow this looks like a Ringbom stirling. No it ain't, I know. But maybe you have that picture in your mind?

Nick

I don't know what kind of valve gear this engine has, if any. He says it doesn't run, which may be enlightning.

But ... Extended, or 'balanced' piston rods were very common on steam engines (including locomotives) at one time (up to ablout 1900 anyway). Early crossheads, or what passed for them, were NOT good, and allowed the pistons to tip in the cylinders. This wore both the piston and the cylinder into elliptical shapes. NOT good. The simple solution was to extend the piston rod through the piston and out through the cylinder head. This, of course, added another packing gland which was a source of different problems as you allude to.

Dan Mitchell ============

It does reach more than halfway through the cylinder. Makes me wonder how the rod is connected to the piston. Maybe I'll dis-assemble that end tonight...

wrb

Ok, I'm thinking the piston shaft is hollow, and the tube fits it very closely.

If that tube goes far enough down that it's exposed to the steam in the outboard end of the cylinder at about the far travel of the piston, then you could make pressure differentials work the valve if you add in a check valve; pressure in the tube (produced when the piston goes to the end of the stroke toward the flywheel) would shift the valve to send steam to the flywheel end (and exhaust the other end). A restriction between the valve actuating cylinder or diaphram and the check valve would ensure adequate pressure to shift the valve, and still allow the pressure produced by the shaft travelling over the tube (forcing more steam up it) to go on out. When the piston reaches the end of the stroke where it's moving away from the flywheel and begins to go the other way the tube starts to carry a vacuum (between decreasing loss of volume and condensation in the loop of the tube), which would shift the valve back.

This could be improved by adding a spring on the valve to work against the tube pressure- as soon as the tube pressure dropped to close to atmospheric the spring would shift the valve against it, exhausting the flywheel end and sending steam to the other.

Can you shift the valve with the pins that stick out? I'm thinking that's how you start the engine, push a pin..

John