finding the throw on an eccentric

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kwoodhands

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I just finished a cylinder with a 7/8" bore and 1-1/4" throw. This is a slide valve steam cylinder type engine.
The inlet steam ports are .394 in between and are .078 wide. Total from out to out ports is .550.
Is there a formula to find the throw on the eccentric. I am guessing that the throw is 1/2 the total of the admission ports, .197
mike
 
I take it you are asking what the stroke of the eccentric operating the slide valve needs to be? And, does the same steam valve chamber supply both steam pressure as well as exhaust porting? In which case, there needs to be a third steam supply port, usually between the two cylinder ports. This is ported by a sliding "spool" valve (if cylindrical) or a "D" valve in a "Steam Chest" box in a double acting cylinder. Just trying to get the picture of what you're building.

A lot more info may be required to answer your question fully, since the length of the moving valve also plays a part in timing. At no time would you want both ports, blocked or pressurized, although venting could overlap briefly. In any event, once you decide what the valve stroke needs to be, the offset of the eccentric would be half of that.
Mark
 
mws said:
once you decide what the valve stroke needs to be, the offset of the eccentric would be half of that.
Click to expand...
So say my max stroke needed in the box was 0.550 then my
eccentric would be 0.275 offset. which would give you a full 0.550 movement when it completes a full revolution. , I know that is not what this one should be but at least from what I on MWS s it is the same as Iwas thinking as well.
Get a few more details and we may be able to help you figure it out. I.e a drawing etc.
 
mws said:
I take it you are asking what the stroke of the eccentric operating the slide valve needs to be? And, does the same steam valve chamber supply both steam pressure as well as exhaust porting? In which case, there needs to be a third steam supply port, usually between the two cylinder ports. This is ported by a sliding "spool" valve (if cylindrical) or a "D" valve in a "Steam Chest" box in a double acting cylinder. Just trying to get the picture of what you're building.

A lot more info may be required to answer your question fully, since the length of the moving valve also plays a part in timing. At no time would you want both ports, blocked or pressurized, although venting could overlap briefly. In any event, once you decide what the valve stroke needs to be, the offset of the eccentric would be half of that.
Mark
Click to expand...

Mark, I needed to know the offset distance from the centerline of a turned eccentric. My guess was correct, .197 which is half of the port distance. I made the eccentric today and tried it out, works well. Now I need to set the eccentric with the piston rod crank.
As far as your questions, the valve chamber has an exhaust port in the center which is twice the width of the steam ports.
This is a D valve type in a double acting cylinder.
thanks, mike
 
Pictures! We like pictures. :) Sounds good! Wish I had more time for steam projects.
 
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