Walschaerts Mechanism

[vederstein]

I've always been fascinated by the valve gear of the later steam locomotives. The fact that is works with only levers and no eccentric is amazing to me.

A little bit of research and I found the mechanism was originally designed by Belgian Egide Walschaerts in 1844. (Wikipedia page here.) Over the years, the mechanism was modified by others, but the core is still a joy to watch for someone that like moving mechanisms.

The mechanism is essentially adding the cyclic motion of two different sine waves. It's more complex than Stephenson's valve gear, but has the advantage that all the parts are on the outside of the engine and not between the rails.

Therefore there really wasn't any reason to use it beyond locomotives and as far as I know, the mechanism was never used on a stationary engine.

Well, I'm going to end that.

I've started the design of a small stationary steam engine using Walschaerts valve gear. I must give credit where credit is due though. I found a CAD model of a Locomotive on Grabcad and scaled the design to my liking. The parts are my own design, but the geometry is not.

It's very early at this point in the design and I'm only working out the motion. I don't have a piston or valve yet. The details like how the links fit together aren't there. I'm just working out the motion.

Comments?

 

[BaronJ]

Therefore there really wasn't any reason to use it beyond locomotives and as far as I know, the mechanism was never used on a stationary engine.

Comments?

The reversing mechanism was used extensively on steam driven pit winding engines as well as early steam driven boats and barges for prop and paddle wheel reversal.

But yes it is a very interesting mechanism.

 

[vederstein]

On these other engines was the valve gear a Walschaerts (or one of its derivatives) or was it the Stephenson's reversing valve gear which used two eccentrics?

From Wikipedia: Stephenson valve gear - Wikipedia

 

[Richard Hed]

I've always been fascinated by the valve gear of the later steam locomotives. The fact that is works with only levers and no eccentric is amazing to me.

A little bit of research and I found the mechanism was originally designed by Belgian Egide Walschaerts in 1844. (Wikipedia page here.) Over the years, the mechanism was modified by others, but the core is still a joy to watch for someone that like moving mechanisms.

The mechanism is essentially adding the cyclic motion of two different sine waves. It's more complex than Stephenson's valve gear, but has the advantage that all the parts are on the outside of the engine and not between the rails.

Therefore there really wasn't any reason to use it beyond locomotives and as far as I know, the mechanism was never used on a stationary engine.

Well, I'm going to end that.

I've started the design of a small stationary steam engine using Walschaerts valve gear. I must give credit where credit is due though. I found a CAD model of a Locomotive on Grabcad and scaled the design to my liking. The parts are my own design, but the geometry is not.

It's very early at this point in the design and I'm only working out the motion. I don't have a piston or valve yet. The details like how the links fit together aren't there. I'm just working out the motion.

Comments?

Veder, Your video doesn't work. I've been thimking about the very thing you are working on. I've always thot there must be a way to work the valve without using an eccentric. Because of ;this, you have shown the way. Thanx.

 

[goldstar31]

My late lamented friend Don L. Ashton wrote extensively ( originally) at his own expense on Walshaert's and Stephenson's Gear,
Originally, he published two books and later a combined one.

When I wrote here of his sad loss, it went down like a lead balloon here but not by other locomotive web sites.
My connection? Don composed music for my wife. He wrote with my late wife's old friend, Richard Redd Ingham the Cambridge Companion to the Saxophone. Don and his broither Eddie ran a music shop on Cadishead, Manchester. Don, amongst other things mentioned here was a world authority on tug boats and had his own full size locomotive.

He was lost on acidic corrosion on BMW cars

 

[BaronJ]

On these other engines was the valve gear a Walschaerts (or one of its derivatives) or was it the Stephenson's reversing valve gear which used two eccentrics?

From Wikipedia: Stephenson valve gear - Wikipedia

The animation looks more familiar ! Though I could not honestly say that I remember particularly.

Its been well over sixty years since my mom and my sister in her pram walked through the colliery yard on the way to town, me stopping to climb the stairs to the winding engine house door, to stand and watch the engine running, lifting or lowering the cages. The engine driver shouting at me to stand by the door and not venture any further.

The smell of steam and those shiny handles and levers, the white band on the big rope wheel with the black line on it, that had to line up with a stationary one so the engine driver knew when the cages were level with the gate.

I ought to title this "Childhood Memories"
Sorry about reminiscing.

 

[tornitore45]

The fact that is works with only levers and no eccentric is amazing to me.

Walschaertsgif - Walschaerts valve gear - Wikipedia
The eccentric is right on the wheel. Is derived from the main crank with a phase offset "cranklet".

 

[vederstein]

Sorry, I had my Youtube animation set to Private and not Unlisted. It should work now.

...Ved.

 

[Richard Hed]

I've always been fascinated by the valve gear of the later steam locomotives. The fact that is works with only levers and no eccentric is amazing to me.

A little bit of research and I found the mechanism was originally designed by Belgian Egide Walschaerts in 1844. (Wikipedia page here.) Over the years, the mechanism was modified by others, but the core is still a joy to watch for someone that like moving mechanisms.

The mechanism is essentially adding the cyclic motion of two different sine waves. It's more complex than Stephenson's valve gear, but has the advantage that all the parts are on the outside of the engine and not between the rails.

Therefore there really wasn't any reason to use it beyond locomotives and as far as I know, the mechanism was never used on a stationary engine.

Well, I'm going to end that.

I've started the design of a small stationary steam engine using Walschaerts valve gear. I must give credit where credit is due though. I found a CAD model of a Locomotive on Grabcad and scaled the design to my liking. The parts are my own design, but the geometry is not.

It's very early at this point in the design and I'm only working out the motion. I don't have a piston or valve yet. The details like how the links fit together aren't there. I'm just working out the motion.

Comments?

exactly where is the valve? I can see several possibilities but nothing definite.

 

[vederstein]

No valve yet. It's very early in the design. No cylinder yet either....

 

[Richard Hed]

No valve yet. It's very early in the design. No cylinder yet either....

Oh, thanx for that. I thot it was the train mechanism. Hope to see your design soon. THis gives me very many naughty ideas.

 

[J Harp]

The return crank affixed to the crankpin gives the same motion an eccentric would.
The curved link, called an expansion link I think, should be pivoted in it's center, not at the end if it is going to allow reversing the engine.

 

[vederstein]

The curved link, called an expansion link I think, should be pivoted in it's center,

Right you are. After I work out the details based on the locomotive CAD model I downloaded, I'll need to modify the design to accommodate the reversing portion.



This design is going to take some time....

 

[comstock-friend]

For the study of many different types of valve gear are the programs of Charlie Dickstader. Charlie has since passed but his work is still available.

http://www.billp.org/Dockstader/ValveGear.html
John

 

[vederstein]

For the study of many different types of valve gear are the programs of Charlie Dickstader.

That is very cool!

Good to keep for reference and initial designs.

It'll be a great assistance in designing these mechanisms.

Thanks!!!