Steam Engine Rotation

[Dan Rowe]

Pat, Stephenson gear is not the only gear with variable lead. The advantages over variable lead and constand lead and other finner points of gear design fill pages and all authors have different slants. I like Peabody as he was the head of the Marine Engineering Dept. at MIT. He states his bias for marine engines and sheds some light on other views.

I am most found of the early 2 cylinder Shays but I like all of them.

The other thing that will flip the logic with Stephenson valve gear is the use of rocker. Most locomotives in the US with Stephenson gear had rocker. Shays ere like a marine engine and have direct Stephenson gear with no rocker. It took me a while to figure out how to make Dockstader work for slide valves and no rocker.

Here is a pop quiz for a Shay 3 cylinder locomotive with D slide valves. The management has decided to change the valves to piston valves.

Shay cranks have the eccentrics keyed to the shaft. the cylinders are numbered 1,2, & 3 from the back to the front. Cylinders 2 and 3 are mirror images of cylinder 1. The eccentrics for cylinder 1 and 3 can be removed off the ends of the shaft. The #2 eccentric is a two piece split eccentric keyed to the middle of the shaft.

Now we have to decide if we need new parts for the valve gear or can we get by with a shop fix?

Dan

 

[Maryak]

for more see attached pdf.

Best Regards
Bob

View attachment SVrot.pdf

 

[Dan Rowe]

Bob,
Which edition of Verbal notes and Sketches is that from? I have the 13th edition on my shelf.

Lookong at Brian's single cylinder overcrank engine thread again made me thing of one more thing that can flip the logic of a steam engine. Just add a return connecting rod. That type of engine has the crankpin 180o out of phase with the normal arrangement. I did not take that in account with my valve study in that thread but just add 180o more to the answer I gave in that thread using Bilgram's diagram.

This is exactly what I was getting at with the Shay question. I know that several of them had after market piston valves added so that would flip the valve logic. If the piston valve has port dimensions to match the D slide valve all we have to do for #1 and #3 cylinder is swap the eccentrics as they are mirror images. The #2 cylinder is not quite as easy if there is room on the split eccentric a keyway could be cut 180o from the original other wise the key in the crank has to be moved.

Dan

 

[Maryak]

Bob,
Which edition of Verbal notes and Sketches is that from? I have the 13th edition on my shelf.
Dan

18th in 2 Volumes.

Best Regards
Bob

 

[blackfoxsteam]

This thread may no longer be active but I have a question regarding JorgensenSteam's Edit 04 on page 2. Is the 55 degrees eccentric advance mentioned for a full sized steam engine what is required to clear the slide valve outside lap (to start admitting steam to the top of the cylinder)?