Steam Engines, part 2

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Steam Engines, part 2
Posted by D.Bernie on Friday, September 28, 2007 11:31 AM

I've seen several steam videos but I can't follow all the adjustments made by the engineer.  I can recognize the throttle, usually overhead, and the two brake handles (engine and train). It is the fourth that mystifies me.  I assume it is the reversing lever, but why would the reversing lever be adjusted in motion?

Bernie

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Posted by dldance on Friday, September 28, 2007 11:40 AM

Welcome to the forums.

 

The engineer has two ways of controlling the amount of steam that enters the cylinders - the throttle and the reverser.  The throttle controls the amount of steam and the reverser controls the length of time that the steam is admitted to the cylinders.  After the train is at the desired speed, then the reverser can be adjusted so that just enough steam is used to keep the train at speed.  That lowers the load on the boiler (and the fireman - for which I am grateful.)

dd

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Posted by wjstix on Friday, September 28, 2007 11:46 AM
Long story shortSmile [:)]: The reverse lever on a steam engine adjusts which end of the pistons the steam goes into; steam going in one end will make the train go forward, steam in the other end will make it go backwards. Once the train is moving, a good engineer can also use the reverse lever to fine tune how much steam goes into the pistons, making the train use steam and fuel more efficiently.
Stix
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Posted by CSSHEGEWISCH on Friday, September 28, 2007 2:03 PM
Just to make things worse, some marine steam engines have separate controls for reverse and cutoff.  There is a steam stern-wheel towboat on display at Keokuk IA which is a tandem compound and has this control arrangement.
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Posted by Semper Vaporo on Friday, September 28, 2007 5:35 PM

 wjstix wrote:
Long story shortSmile [:)]: The reverse lever on a steam engine adjusts which end of the pistons the steam goes into; steam going in one end will make the train go forward, steam in the other end will make it go backwards. Once the train is moving, a good engineer can also use the reverse lever to fine tune how much steam goes into the pistons, making the train use steam and fuel more efficiently.

Not quite.  Short story LONG...

Steam goes into both ends of each cylinder no matter which way the locomotive is going, but not simultaneously.  The valve gear changes the timing of the admission into the cylinder (either/both ends) to control which way the wheels are pushed/pulled by the main connecting rod.

If the piston is in the middle of the cylinder and steam is admitted to the front then the piston will be pushed back, but whether that moves the wheel clockwise or counterclockwise depends on whether the point where the connecting rod connects to the wheel (the main pin) is at the top of rotation or bottom.

Assume you are looking at the right side of the locomotive with the wheels to the left of your view and the cylinder to the right.  If the main pin on the wheel is at the top, then the piston will be centered in the cylinder.  If you put steam in the front of the cylinder the piston will be pushed back and that will push the wheel to rotate counterclockwise.  If you put steam in the back of the cylinder the piston will be pushed forward and the connecting rod will pull the wheel to rotate clockwise.

The wheel will rotate until the piston is all the way to one end of the cylinder.  Inertia (or power from the another cylinder, i.e.: the one on the other side of the locomotive, which will now be centered in its cylinder and pushing or pulling the wheels in the same rotational direction) will cause the wheel to continue its rotation.  It is at this point that the valve gear swaps the port where the steam is admitted to the cylinder so that it pushes the piston in the opposite direction.  And the wheel rotation continues in the same direction.

i.e.: if the main pin WAS at the top (12-o'clock) and the piston was being pushed forward because steam was being admitted to the rear of the cylinder, then the main rod will pull on the main pin to cause the wheel to rotate so that the main pin moves to the closest point to the cylinder (3-o'clock), and has rotated just past that point.  Steam is now admitted to the front of the cylinder to push it back toward the rear and the wheel continues to rotate because the main rod is now pushing on the main pin on the wheel.  This continues until the piston is at the back of the cylinder and the wheel has rotated such that the main pin goes past the bottom most position (6-o'clock) and moves to the farthest point from the cylinder (9-o'clock).  At this point the valve gear again swaps the port receiving steam to the rear to force the piston again forward, which causes the main rod to again pull on the main pin to continue the rotation of the wheel in the same direction (back to and past the 12-o'clock position).

This process of swapping which end of the cylinder receives steam is continued throughout the rotation of the wheel and produces continuous movement in the desired direction of the locomotive.

To reverse the locomotive, you just alter which end of the cylinder receives steam "first".

Oh and one more thing.  When the valve gear is such that steam is going in one end of the cylinder the other end is open to exhaust the contents of that end (so the piston can move).

 

 

Semper Vaporo

Pkgs.

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Posted by J. Edgar on Friday, September 28, 2007 8:35 PM

 

 this is a Walschaert type of valve motion.....going from forward motin to reverse motion....red being live steam and blue exhaust....the reverse lever in the cab thru levers or a steam\air operated piston would move the radius bar up and down in the link...in this diagram it happens when the motion stops.....where the radius bar is postioned in the link determines the duration of valve opening and the amount of steam allowed in...short little spurt like when moving at high speed or full stroke allowing lots for starting off

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Posted by wjstix on Monday, October 1, 2007 3:44 PM

Yup Semper, just like I said...if the engine is sitting still, admitting steam on one side of the piston will make the train go forward, the other side will make it go back. Now whether admitting steam to the front of the piston makes the engine go forward or backwards, that depends on positioning of the rods & valve gear. 

I know how it works, I just didn't want to spend a half hour explaining it in detail!! Big Smile [:D]

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Posted by dinwitty on Monday, October 1, 2007 7:17 PM

baker valve gear has this innotavative linkage device that controls the cutoff, all while its being moved around by all the attached linkages.  The engineer pushed the lever full forward there would be minimal cutoff, just about all maximum steam flies to the cylinders. Good for train starting and slipping drivers if the engineer isnt careful on the throttle. But at speed you don't need all that power so the engineer will back off the lever and cutoff the steam delivery.

 

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Posted by J. Edgar on Monday, October 1, 2007 8:26 PM
 dinwitty wrote:

baker valve gear has this innotavative linkage device that controls the cutoff, all while its being moved around by all the attached linkages.  The engineer pushed the lever full forward there would be minimal cutoff, just about all maximum steam flies to the cylinders. Good for train starting and slipping drivers if the engineer isnt careful on the throttle. But at speed you don't need all that power so the engineer will back off the lever and cutoff the steam delivery.

 

    ............Baker valve gear had all kinda small lil parts flyin around...to hard to follow....Joy valve gear looked like a grasshopper with the twitch......Southern valve gear looked like Walschearts on its side.....all of these had cut-off control...the closer the radius rod is to the center of the link the more steam is 'cut-off'....Baker was just slightly more precise and had less inheirant creep in valve postion
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Posted by dldance on Tuesday, October 2, 2007 11:33 AM
 dinwitty wrote:

baker valve gear has this innotavative linkage device that controls the cutoff, all while its being moved around by all the attached linkages.  The engineer pushed the lever full forward there would be minimal cutoff, just about all maximum steam flies to the cylinders. Good for train starting and slipping drivers if the engineer isnt careful on the throttle. But at speed you don't need all that power so the engineer will back off the lever and cutoff the steam delivery.

 

Minimum cutoff is rough on fuel consumption (and the fireman!)

dd

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Posted by switch7frg on Thursday, October 18, 2007 11:07 AM
J Edgar  ; A very fine exhibit  and description of the way things go round  and why . Thank you . Respectfully , Cannonball ( another Jim)

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Posted by J. Edgar on Friday, October 19, 2007 7:34 PM

 switch7frg wrote:
J Edgar  ; A very fine exhibit  and description of the way things go round  and why . Thank you . Respectfully , Cannonball ( another Jim)

 many thanks ....just here sharing whatever my lil mind has

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