# Simple valve gear



## Amber (Jul 29, 2011)

On my boiler thread, Ralph suggested that I look into the Hackworth valve gear, so I did an internet search, and among other things, I came up with this web page. This is the Marshall gear, a lot like the Hackworth gear,but without the slide block. This looks interesting, what do you think?
http://www.martynbane.co.uk/modernsteam/klr/badger.htm


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## ralphbrades (Jan 3, 2008)

Miss Amber , 

I like! The reason I suggested the Hackworth is that everybody makes the die block from a sawn length of rectangular steel box section tube. 
This simply returns everything to levers and should be easy to fabricate. 

regards 

ralph


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## Old Boy (Feb 9, 2009)

Someone also suggested downloading Charlie Dockstader's valve gear programs, which is a good suggestion, and I don't recall exactly if he referred to it as a valve gear "design" program, but if so this would be a bit of a misnomer. Many people (including myself) have been surprised to discover when first using it that it's not a valve gear design program per se. Dockstader is a proofing program, in that you design your valve gear by the usual means (on paper or Cad from books and formulae) and then plug the values (dimensions, etc) into Dockstader to find out what you've got and how well it performs. You then can make adjustments within the program to optimize your gear, and proof it, before it becomes metal and a part of the locomotive. It would perhaps be better to think of it as a very handy valve gear design TOOLS. However it's not all cake, IIRC a full Walschearts gear (and associated frame points) has around 57 variables!


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## Semper Vaporo (Jan 2, 2008)

I am the one that suggest it... and I agree it is not really a "Design" program. You cannot just arbitrarily pick odd components or invent new ones and build some heretofore unseen valve gear design.

You can, however, pick an existing design, such as "Hackworth with Outside Admission" and then substitute dimensions that your engine has (or is going to have) to see what other dimensions must change to so that all the parts fit. But that is a bit of a trial and error thing that way... Better to know how to do the math to pick the exact dimensions.

Once you have the dimensions inserted in the program for that particular design of gear then you can see if it produces the desired timing in both forward and reverse and you can make adjustments to test for what happens with variances in component mounting position or the lengths of rods and levers.

Like I said in the other thread, I have not attempted to design with it... I get much too distracted watching the parts move in the animation. It is a good way to study the parts and why they are connected in the way they are, and being able to advance and reverse the motion in small increments you can zoom in on parts (like the actual valve openings) to see what is happening and when it happens.

I spent a lot of time once with the Walshaerts Valve gear changing the dimensions of the Combination Lever to see how that affects the Lead and how to change the valve Lap to compensate for the changes.

It is noted in the design notes for the program that the values given in the examples are not necessarily the best design for that gear within the given overall dimensions of the engine as a whole.


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## xo18thfa (Jan 2, 2008)

Hackworth gears may look "simple", but there is still a lot of geometry in there that if is not done right, you will have a mess on your hands. Charlie Dockstader's program is not a design tool. It is a testing program. You have to do the math and design stuff and entry the results in the program.


Study simple eccentrics first. Understand lap and lead, port size, cavity size on the D valve and all that.


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## Pete Thornton (Jan 2, 2008)

The valve gear on the Cheddar "Philadelphia" looks really simple. I wonder if anyone knows how it works . .


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## spincaster (Mar 10, 2012)

One of the nice things about Hackworth is that it is easy to design and easy to build compared to walsharts and stevensons. Charlie's software is great to test your design. There are other similar gear like the previously mentioned marshal gear that are simpler yet.


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## Gary Armitstead (Jan 2, 2008)

BTW, just a side-note here. Charlie Dockstader passed away last year. He gave me lots of tips on my Stephenson valve gear, when I started my Gene Allen ten-wheeler. He built a 1.5" 4-10-0," El Gobernador". Great guy, beautiful locomotive!


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