Does anyone have any diagrams or explanation for how the indirect Walschaerts configuration operates? I have been trying to figure it in my head for a while and there are some aspects that don't add up to me.
Thanks, Casey

"Direct" motion is driven from the same end of the link which is hooked to the eccentric crank. "Indirect" is driven from the opposite end; so, we refer to a locomotive that has the radius rod at the bottom in forward gear as direct, and at the top as indirect. To reverse it, you make it the other way, but we refer to it based on forward setting only. Remember, the top of the link always swings in the opposite direction from the bottom since the link is pivoted from a fixed point in the center.

Stephenson gear is direct in both directions, since both ends of the link are each driven individually by seperate eccentrics. It's center support is not fixed, but free to move on a hinged hanger.

Slide valves admitted steam from the outside ends of the valve, and exhausted from the center. Piston valves were the opposite, admitting from the center and exhausting at both ends. When a slide valve was converted with a piston valve conversion kit, a special piston valve design for outside admission was used. By looking at the combination lever on Walschaerts, you can tell whether it is for an inside or outside admission valve depending on what is connected on top: the radius rod or the valve stem. That's because lead is derived from the bottom connection of the combination lever, and what's lead in one admission is antilead in the other. Maybe we should call it follow........but that would be confusing.

There are some very good books on valve gear used by the Live Steam modeling fraternity. To get in deeper you can probably find some through those web sites.

Thanks for asking an interesting technical question.

dave

Oh, I forgot: you (obviously) have to have the crank around on the other side of the center or it will try to move the valve the wrong way!

dave

Casey,

Are you asking about the valve train found on the US Army 610 at Tennessee Valley Railroad Museum and the 557, recently moved to Alaska? Both of these have what we would call reversed Walscherts valve gear. If this is what you are asking about. The explanation is fairly simple (depending on how much depth we go into.

In short the entire valve train is the same on both types of valve trains, in other words, all of the parts are the same, all of the parts are included and the general principle of both is the same. The single biggest change is the placement of the eccentric on the crank pin.

Take a look at say 844, 3751, 261, or any other Walscherts valve train. The eccentric, which the piece that is located on the main crank pin where the main rod meets with the drive train is positioned off center (thus the name eccentric) with the center of the axle. (modeling note, some model steam locomotives have centered eccentrics so that the valve train does no move....or has very little motion.)

If you can look at a direct side view of any of the locomotives noted above, when you look at the eccentric, you will see that the top of the eccentric, where the eccentric rod connects to the eccentric is slightly ahead of the center of the axle. This is normal for Walschaerts valve gear. However, on the 610 and the 557 (US Army S-160 class) the eccentric, when sitting in the same position as noted above will be slightly BEHIND the center of the axle on the main driver. The outcome is; to achieve forward motion, with eccentric trailing, the radius rod would be at the top of the expansion link, rather than at the bottom on a normal (leading eccentric) Walschaerts valve train.

A few basic steam locomotive drive train facts are as follows: Generally in the USA (and the world really) Right hand crank pins lead left hand in forward motion. Generally, eccentrics on outside motion lead, rather than follow. Generally, forward motion is found in the bottom of the expansion link, not the top.

I looked at a few books today looking for an actual diagram of reversed Walschearts, I can not find one. I found one minor mention of placement of eccentrics for reverse motion Walschaerts, but no pictures.

I looked at ITC Locomotive Valve settings, Valve Settings by Collins and Locomotive Vale Setting by Britton.

The only one of those three that mentions the word INDIRECT Walschaerst is Collins book, giving a much more abbreviated explanation than I have above. This is as close as I could come for you.

I hope this helps,

Kindly,

HI John

The information that I am going to post , came from a Book called Locomotive Valve Gear Setting , by Jack Britton published in 1926 . Pat .

An old video of mine of 610. Skip to about 5:20 for pacing shot with the valve gear motion.

http://www.youtube.com/watch?v=diq7tqY1 ... ature=plcp

Pat,

The book you mention is the same book I had mentioned in my post. The problem with this section of Britton's book is that the drawing you have included, as well as the text comes from the section entitled Shop Hints. This section is designed to help shop crews diagnose a valve setting problem, and fix said problem. As such, Britton was very good about laying out all possibilities. Indeed, these are all options.

I disagree with Britton some-what in a minor area. By 1921 (date of this, the second edition) it was well established practice that locomotives were generally right hand lead crank pins and that a radius rod was generally down for forward motion. I am unable to find what the first edition copy or date of the book was. It is possible that the first edition was written in the late 1800's, which would provide more validity to the comment as indeed, up to the late 1800, the practice was still somewhat undefined. However, it is not until the early 1900 shop manuals that we even see Walschaerts valve gear or an explanation there-of.

Thanks for posting the pages and the diagram.

Kindly,

Soo Line #1003, on which Diversified Rail Services is currently completing a 1472-Day Inspection, is equipped with INDIRECT Walschaerts valve gear as built by ALCO in 1911.
Yes, on the 1003 the radius rod is in the top of the link when in forward gear and the eccentric crank leads the center of the main driver. I can't see any advantage of this arrangement since the valve gear components are under much more stress with this INDIRECT layout. Also, early in her Soo Line career, a master mechanic at the Shoreham Shops IIRC, developed an attachment of the union link onto the front of the main rod, near the rear of the crosshead shoe which function I think was to add a little more lead. This did not last long as I think the pieces got flung off the main rod at mainline speeds. The better placement for the union link attachment is at the wrist pin as you see on TVRM 610 and NKP 765.

What would be the possible advantage of indirect Walschaerts, and how easy would it be to make it direct?

Here is an archive of Charles Dockstader's valve gear simulator programs. Each type is its own executable file; there is no main page. The simulations consist of line animation with slide controls that let you adjust throttle and reverser. Very intriguing and educational to play with. Plenty of types you've likely never heard of, too.

http://www.billp.org/Dockstader/ValveGear.html

In this case they are offered in .zip compressed files. Just unzip and toss them in a folder. When you download other .zips you can put the unzipped files in the same folder. Click on the .exe for whatever one you want to play with. I believe these are the same files I've had for years through multiple computers.

Steve

I have wondered about this for some time, i.e. the Walscheart gear where the eccentric crank leans away from the cylinder when the side rods are in the bottom quarter, and the radius rod is in the upper part of the link in forward motion. My father (a railfan, not a "tech" type at all) used to call this the "backward extension Walschaert gear." Now I see there is a proper term for it, the "indirect" or "reversed."

I realized recently that all of the Canadian National and Grand Trunk Western 4-8-2s from class U-1-a through U-1-c (6000-6041) appear to have had this type of gear. A good example is No. 6034, below, which my brother photographed in 1958.

From photos I can find, the U-1-d class appears to have had the standard type of Walschaert gear. as did the "bullet nose" U-1-f delivered in 1944. It looks like the U-1-e class had Baker gear.

Can anyone suggest what possible advantage this "reversed" arrangement conferred, and why 42 Mountain types erected in the 1920s would have been so equipped?

.

A question above was:

How easy would it be to make it direct? Kelly answered that in a way. It really has to do with space and what they had to work with and what the railroad wanted. In the case of the US Army Locomotives, I see no reason, in terms of space or limitations there-of why they were not direct in the first place. I go back to; Direct valve gear fails forward.....why would not want a failing forward situation?

In the case of the US Army locomotives, it is not all that easy to convert them. You would have to change and or adapt a number of items. Don't get me wrong, it can be done, but it would not be a simple 30 minute change out of items and down the road you go.

I posted on Trainorders that the records for these locomotives are kept in the US Army Locomotive silo located deep in the heart of area 51, NM. Having seen the silo and having had the chance to search the records I have not come up with a written reason why the US Army did this.....it is still a mystery to me. I know the records related to this exist. On another note, while at area 51, I did see the aliens, so that mystery is solved.....now we are left with the valve gear mystery as our only real question out of area 51. (joking.....but, what part?)

Kindly,

I think this clears it up - the idea of indirect Walschaert gear was sent from other planets if not universes.

Either derivative of the gear - direct or indirect - can provide good valve operation and events when well designed and maintained. I wouldn't sweat the idea of conversion, just doing the best i could with what I've got to work with.

dave

I drew out a force analysis on the Walschaerts valve gear link/link trunnion with the radius rod providing a resistant force and the eccentric rod providing a pushing force on the link. After summing up forces in the x-direction, it appears that the resultant thrust on the the link trunnion/bushing with an indirect motion configuration is twice as much as with the direct motion config. having the link block in the lower portion of the link for forward gear. The only possible advantage I can think of for the application of the indirect valve gear is for a locomotive that would need to run in reverse more than in forward. If this was the case, an indirect valve gear would have the link block in the lower portion of the link for reverse motion and the undesirable link block slip would be eliminated as well as the excessive thrust. I'm not claiming this to be the reason for the design of an indirect motion, but an interesting possibility I think. I am also speaking strictly regarding the Walschaerts valve gear.

Casey