Stephenson Valve Motion Dilemma...
| July 23, 2001 04:28PM |
Calling all techies!
This is quite rare, but I've noticed on some smaller 3' engines and a few 30" & 2' engines, a nonstandard arrangent in their Stephenson valve motion where the Rocker Arm pivot (the Rocker Box) is mounted directly below the pivot point of the Lifting Arm. How do they interact with the Link in this posistion?
One one can be attached directly to the Link, how does the other work?
---
For those who came in late...
Everyone knows about the Johnson Bar in the cab. Well on a Stephenson valve gear the rod going from the Johnson Bar goes up front to a lever that rotates the Lifting Arm. The lifting arm raises and lowers the cressent shaped Links.
The Links are attached to a pair of Eccentrics on the drive axle, by way of the Eccentric Arm, so that they rock back and forth as the wheel turns. The Links have cressent shaped slots in them that a Link Block rides in.
A bolt through the Link Block attaches it to the Rocker Arm. Thus as the Wheels rock the Links to and fro the Link Blocks make the Rocker Arm...well..rock back and forth.
The other end of the Rocker Arm shifts the valve back and forth in the Steam Chest
Normally the pivot point for the lifting arm is several inches back on the frame from the Rocker Box. The Lever from the Johnson Bar is mounted vertically as opposed to the Lifing Arms that are horizontal (parallel to the centerline of the Cylinders).
Thus the ends of the Lifting Arms stick out infront of the Lifting Arm pivot point. A short link (the Lifting Link) hangs down from the ends of the Lifting Arms to connect to the Links. Since the Link Block is mounted in the center of the Links, the Rocker Box is mounted on the frame vertically under the ends of the Lifiting arms (or damn close to that point).
This puts the pivot point of the Rocker Box infront of and below the pivot point of the Lifting Arms.
The puzzle I raised is how does it work when the Rocker Arm pivot point is directly below the Lifting arm pivot point.
A) How does the Lifiting Arm lift the links if they are directly below its pivot point.
Or the probelm is:
How is the rocking motion of the Link Block conveyed back to the Rocker Arm?
---
Thank you all for your time,
Curtis F.
This is quite rare, but I've noticed on some smaller 3' engines and a few 30" & 2' engines, a nonstandard arrangent in their Stephenson valve motion where the Rocker Arm pivot (the Rocker Box) is mounted directly below the pivot point of the Lifting Arm. How do they interact with the Link in this posistion?
One one can be attached directly to the Link, how does the other work?
---
For those who came in late...
Everyone knows about the Johnson Bar in the cab. Well on a Stephenson valve gear the rod going from the Johnson Bar goes up front to a lever that rotates the Lifting Arm. The lifting arm raises and lowers the cressent shaped Links.
The Links are attached to a pair of Eccentrics on the drive axle, by way of the Eccentric Arm, so that they rock back and forth as the wheel turns. The Links have cressent shaped slots in them that a Link Block rides in.
A bolt through the Link Block attaches it to the Rocker Arm. Thus as the Wheels rock the Links to and fro the Link Blocks make the Rocker Arm...well..rock back and forth.
The other end of the Rocker Arm shifts the valve back and forth in the Steam Chest
Normally the pivot point for the lifting arm is several inches back on the frame from the Rocker Box. The Lever from the Johnson Bar is mounted vertically as opposed to the Lifing Arms that are horizontal (parallel to the centerline of the Cylinders).
Thus the ends of the Lifting Arms stick out infront of the Lifting Arm pivot point. A short link (the Lifting Link) hangs down from the ends of the Lifting Arms to connect to the Links. Since the Link Block is mounted in the center of the Links, the Rocker Box is mounted on the frame vertically under the ends of the Lifiting arms (or damn close to that point).
This puts the pivot point of the Rocker Box infront of and below the pivot point of the Lifting Arms.
The puzzle I raised is how does it work when the Rocker Arm pivot point is directly below the Lifting arm pivot point.
A) How does the Lifiting Arm lift the links if they are directly below its pivot point.
Or the probelm is:
How is the rocking motion of the Link Block conveyed back to the Rocker Arm?---
Thank you all for your time,
Curtis F.
| Subject | Author | Posted |
|---|---|---|
|
Curtis F. | July 23, 2001 04:28PM |
|
Jim Adams | July 24, 2001 06:51AM |
|
Marty Knox | July 24, 2001 05:28PM |
|
Howard johnson | July 25, 2001 01:54AM |
|
Curtis F. | July 25, 2001 08:47AM |
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