How to start Walschaerts Design as a beginner?

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baggo
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Re: How to start Walschaerts Design as a beginner?

Post by baggo » Tue Dec 30, 2014 6:55 am

I wouldn't worry too much about the Reversearm parameters. They don't affect the valve events as such, just the max cut off that you get when the reverser is set to full gear.

As you suggest, the maximum achievable cut off is determined by the valve and port dimensions and not by the valve gear. Think there's a formula for calculating it in Martin Evan's book on valve gears.

For your interest, here's the diagram that the Wallace simulator produces. Each pair of lines represents the inlet, cut off, exhaust open and close at each end of the cylinder so you can easily see how matched they are. This is one I did for Fred's Milner Hunslet.

John
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Milner Hunslet Valve Gear Recalculated Results 1.jpg
Secretary of The National 2½" Gauge Association
Member of North West Liecestershire SME

http://www.modeng.johnbaguley.info

Dor_Crank
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Location: LA, CA

Re: How to start Walschaerts Design as a beginner?

Post by Dor_Crank » Tue Dec 30, 2014 6:48 pm

John,

Assuming the pairs of curves reflect forward and backward properties, they look very close to each
other. That I understand is hard to accomplish.

I've looked at Don Ashton's spread sheet and found many many variables not described there. I don't have
his manual with me at this moment but I can check later. How did you interpret them? Your layout drawing
must of been pretty perfect and the numerical values derived from the it were also perfect to use his
software!

Was the valve gear layout scaled directly from the Hunslet's prototype drawing? My model is of freelance
so I'll be in the dark more or less.

Dorian

Dor_Crank
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Re: How to start Walschaerts Design as a beginner?

Post by Dor_Crank » Wed Dec 31, 2014 5:45 pm

John,

I'm writing this as I'm trying to get familiar with Wallace's simulator. These step discoveries would
be elementary for anyone who had struggled thru his program but hope it'll be beneficial for others.

I've unziped the simulation software and was able to run the default based graphic from Wallace's
simulator. What's nice about Wallace's is that the graph doesn't keep disappearing as you zoom in.
It's easy to pan up/down/rt/left. And, the valve opening/closing motion is shown at the top of the
valve gear diagram being stationary and big.

Found how to input valve gear parameters: View --> Edit --> select tab of desire -->
type in numerical values --> hit X to exit edit session. Short cut to editing is to double clicking the
diagram screen. To execute: View --> Movie --> See diagram moving but the menu bar greys out.
Nice so far. But the Wvalve.txt doesn't tell you how to stop the motion. Well, just click anywhere
on the diagram screen and it well stop. This took me time.

But where is the parameter description? Tried: Double click anywhere on the diagram to stop motion -->
See menu at the bottom --> Click 'A' (Annotate) button --> See alphabet labeling on the diagram. I like
this annotation better than the Dock's bar displays. My model is of outside admission so I had to go
search for other input data file listed under the 'file' menu bar at the top. Found JW0.L4 and JW1.L4
file to be suitable. These file names appear as 'John Wakefield' under View-->Edit-->Other tab.
But the upper part of the combination lever is not connected!! I guess that's just a software bug.
Under this 'other' tab, there is a motion speed control bar. I've found JW files won't move fast enough
despite setting the bar tab all the way to the right. Later, I've found you can choose Walschaerts
inside or outside admission type by 1st enter: file --> ValveGear --> <Walsch1/Walsch2> for this.
This selection of Walsch1 or 2 would be useful for initial input of a new gear. For a specific input file
of any gear data (whether I or someone else had created), I can do file --> open --> <file name>.

Ok, I'm now ready to go into a nitty-gritty of individual valve gear parameters (interpretations).
For a start, I think the tiny x,y subscripts for e.g., DGx, DGy means horizontal and vertical offset.
I hope I won't encounter bogus or implicit parameters as that of Dock's simulator.

Dorian

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VGC
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Location: Europe / Earth - yet in freedom ;-)

Re: How to start Walschaerts Design as a beginner?

Post by VGC » Tue May 26, 2020 12:05 am

To avoid starting a new discussion treat, I use this one to publish a temporary access URL to my valve gear design program. It will be deactivated again after some time.
Here comes the temporary access info:
https://www.constructor.valvegear.de/ac ... gear.de&qs
Have fun testing it!
Online program for valve gear design:

ValveGear Constructor [EN]

Image

(New: Website also in English language, now much more user-friendly!)

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VGC
Posts: 65
Joined: Tue Sep 22, 2009 3:17 am
Location: Europe / Earth - yet in freedom ;-)

Re: How to start Walschaerts Design as a beginner?

Post by VGC » Sat Apr 10, 2021 4:28 pm

After several months of weekend work on the program, now there is a large update concerning English translatoon of the whole website, much easier access for website visitors and many other (rather hidden) little changes.
See the program weblink in the signature of the comment above and enjoy the temporary access option!

Old Bill
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Location: Leicester UK.

Re: How to start Walschaerts Design as a beginner?

Post by Old Bill » Wed Apr 21, 2021 3:54 pm

Hello friends!

Please may I stick my oar in and ask for some advice? I am in the process of laying out Baker gear for a 1 1/2" scale mountain loco and am using Mr Dockstader's software. As has been discussed earlier, it is not instantly obvious to use but I have persisted and am getting the hang of it such that I have a potential solution. The question now is what constitutes a good solution? What are good valve events so what am I trying to achieve? I want about 1/64" of lead so in mid-gear I get this:

Image

The lead is fine and, although the laps are different, I can make the valve to suit. Here is the Sine chart as well.

Image

I set up the steam chart for nine reverser positions from mid to full forward gear and get this.

Image

The chart doesn't tell me a lot but comparing the cut-offs between front of cylinder on the right and rear on the left, they are not identical but almost match my 75% cut-off target in full gear. (Don Ashton's recommendation). They do diverge in the mid-range so my question is, is this significant and will it matter?

As you can see below for the same set-up but in reverse, they differ more significantly and you can see the bias in the shape of the chart.

Image

I just don't have a feel for what are 'good' valve events so I would very much appreciate some views.

I would like to take this opportunity to thank the late Mr Dockstader for making this programme available and saving me so much time on the board!

Cheers!

Steve

Moron
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Re: How to start Walschaerts Design as a beginner?

Post by Moron » Tue Apr 27, 2021 8:46 am

Old Bill wrote:
Wed Apr 21, 2021 3:54 pm
Hello friends!

Please may I stick my oar in and ask for some advice? I am in the process of laying out Baker gear for a 1 1/2" scale mountain loco and am using Mr Dockstader's software. As has been discussed earlier, it is not instantly obvious to use but I have persisted and am getting the hang of it such that I have a potential solution. The question now is what constitutes a good solution? What are good valve events so what am I trying to achieve? I want about 1/64" of lead so in mid-gear I get this:

Image

The lead is fine and, although the laps are different, I can make the valve to suit. Here is the Sine chart as well.

Image

I set up the steam chart for nine reverser positions from mid to full forward gear and get this.

Image

The chart doesn't tell me a lot but comparing the cut-offs between front of cylinder on the right and rear on the left, they are not identical but almost match my 75% cut-off target in full gear. (Don Ashton's recommendation). They do diverge in the mid-range so my question is, is this significant and will it matter?

As you can see below for the same set-up but in reverse, they differ more significantly and you can see the bias in the shape of the chart.

Image

I just don't have a feel for what are 'good' valve events so I would very much appreciate some views.

I would like to take this opportunity to thank the late Mr Dockstader for making this programme available and saving me so much time on the board!

Cheers!

Steve

Here’s my 2 cents for what it’s worth, at least worth messing with on the program. First of all, I would try and get the laps and leads equal, the the rest of the valve events will behave much better if you do, especially when hooking up the reverser. Lap is a product of valve dimension, but lead can be altered by the combination lever. If you would like, I can include 2 simple formulas that will help you get the exact points you need. 1 from the greenly/Evans book, the other from the original ICS books. Once you enter these in, I just adjust the Union link with the gear rolling slowly in center a thousandth of an inch at a time until the leads/cut-offs are equal. I would also just choose a decimal point for your lead instead of an exact fraction just to make it easier. .015” or .016” will work well. 2nd, I would recommend making your full cut off closer to 85%. I don’t know the prototype you are modeling (except that it’s a mountain) but most American prototype locos had a cut off around 85%. Some higher some lower. Ashton’s book is interesting, but you have to remember the British were much bigger into economy than we are. And most of their live steamer tracks were flat compared to ours. Some American fast freight engines were around 77-80% cut off, but most stuck around 85. Mountain climber got as high as 88-90. The berks were 79-80 I believe. And 3rd of all concerning the cut-offs you are getting, your valve events actually look pretty good. Something to remember with Baker, it usually give unequal port opening front and back, and always give unequal cut-offs from forward to reverse, it’s just the nature of the beast with baker. The berks right out of Lima had pretty unequal valve events, yet they worked well and sounded fairly square. Although when flying hooked up super high, they sounded more like a gallop than a helicopter. But obviously, their overall performance was never affected as they were phenomenal fast freight locos. Hope this helps, let me know if I can help further and I will try my best.

Old Bill
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Location: Leicester UK.

Re: How to start Walschaerts Design as a beginner?

Post by Old Bill » Thu Apr 29, 2021 1:41 pm

Hello Moron!

Thank you so much for taking the trouble to reply. I really value your input. Not being able to get around and talk to people at the moment is a killer!

The prototype is the Frisco 1500 class but an early one with Baker gear. Baker gear is pretty rare this side of the pond and very few people have experience of it so I have been struggling. As you can see, I have managed to get the lead even within a thou but I was very surprised that the laps were different. I used a Bilgram diagram to identify the lap dimensions and this generated differing figures front and rear. I did it several times and came up with the same answers each time. I believe that it is due to the effects of crank angle. Should I just take a mean figure for the lap?

It is very nice to hear your comment that Baker gives unequal cut-offs forward to reverse. That is exactly the sort of gem I have been after because I don't know what to expect and whether it is just my incompetence or it actually does that!

I shall run it again and see if I can get 85% and also see what happens when I adjust the lap. I will let you know how I get on.

Very many thanks for your assistance.

Kind regards,

Steve

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Marty_Knox
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Re: How to start Walschaerts Design as a beginner?

Post by Marty_Knox » Thu Apr 29, 2021 2:30 pm

Baker Valve Gear does not travel the same distance either side of center between ports. Baldwin made the front and back bushings different lengths to compensate. They gave you a dimension to add to one end and subtract from the other end. Here is the diagram from Baldwin Standard Practices.
Baker VG bushings.jpg

Old Bill
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Re: How to start Walschaerts Design as a beginner?

Post by Old Bill » Thu Apr 29, 2021 4:43 pm

Another gem! Thank you Marty. These are exactly the details I am looking for!

Steve

Old Bill
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Location: Leicester UK.

Re: How to start Walschaerts Design as a beginner?

Post by Old Bill » Thu May 13, 2021 3:58 pm

Hello Friends!

I am still playing with this and looking at the lap at the moment. As I said before, I have used a Bilgram diagram to work out the laps and came up with different values front and rear. They gave me this chart which has the same settings as above:

Image

You can see that the exhaust ports open at the 50% piston stroke position.

I then took the mean lap, changed the valve dimensions to achieve this value at both ends and got this output, again for forward gear:

Image

Now, the exhaust ports open at the 45% stroke position in mid gear. All of the openings are biased with the piston closer to the front end although it seems to be less significant as we approach full gear. I suspect that there will be little effect so think I shall make the valves like this for simplicity sake. What do you think?

Full forward gear here is 75%. The next thing I shall try is to achieve a longer cut-off. Watch this space!

Steve :)

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VGC
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Re: How to start Walschaerts Design as a beginner?

Post by VGC » Sat May 15, 2021 10:34 pm

Hello Steve,
could you also post some diagram for bakward gear?
I would be glad to see in this diagram if (or how much) it is really true that Baker valve gear was rather weak on riding backward.
Best regards
VGC

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