Steam Control Question - Throttle versus reversing lever?

jblodgett

jblodgett

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Let's see if I can post this in the correct area this time! :)
I am new to live steam, having purchased a used Ruby to learn about it while lusting over the new Accucraft 13T Shay. The Ruby, as obtained, was setup so that the lever in reverse makes the loco move forward. It has an R/C setup to control the throttle, with the lever positioned to the rear (for forward). I was surprised to learn that the Ruby (as set from the factory) tends to run better in reverse than forward because of where the steam is admitted to the valve chambers. I have since seen a YouTube video that explained that when in forward as built, the steam enters and presses on the valve at the front, forcing it backwards and adding friction to the whole system. By reversing the cams underneath and thus using the lever in the "normal" reverse position to now be forward, the steam enters the valve chamber from the side (via the “normal” exhaust port) and eliminates that frictional issue. Having watched several YouTube videos on the Accucraft 13T Shay, I noticed that the ones I have seen have the r/c servo move the lever while the throttle is just left in one position. Besides giving control of steam this also allows control of direction all with just one servo. At the moment I can’t see the difference between controlling how much steam actually gets to the cylinders, whether controlled by the throttle (how much steams gets any farther) or the forward/reverse lever (which moved the centre valve on the Ruby, which says how much steam gets that last leg of its journey). But there may be subtle things I don’t understand. Of course it might be entirely different on the Ruby compared to their new Shay which prompted these thoughts. I would love to hear the thoughts and advice on this from those with long and hard won experience.
 
Be careful, not all locos speed can be controlled by using the reversing levers. There is a difference in the steam motors, I'll dig out my explanatory bumph if I can find it. My Accucraft locomotives are geared (sorry) up to be controlled by the reverser, but my Roundhouse isn't, it will actually damage the linkages if you do. If you can use the reverser, I find it easier to control, and it will bring the engine to a stop a lot quicker in emergencies
 
Paul has pretty much hit the nail on the head. For safety you should always close the regulator before changing direction. When loco is stationary regulator should be set so that no steam exits the boiler via the regulator and the forward/reverse set to central ie neither forwards nor backwards.

Some locomotives are likely to crepe forwards or reverse if the regulator is closed but the direction set one way or the other, I have a Roundhouse loco that is very guilty of this.

It should also be noted that most locomotives in our scale do not have a true Walschaerts gear thus ‘notching up’ is not possible, attempts to do so with the gear in part one way or the other will result in lumpy running and as Pauls says could damage the gear.

Exceptions to the rules do exist, Merlin locomotives for example had a regulator/reverse worked from a single RC servo.
 
I have a RH loco that as explained by both P Paul M and dunnyrail dunnyrail use the regulator to control speed, and forward/reverse to control direction, however I understand that some Accucraft locos use the Forward/Reverse for both direction and speed. As an engineer this to me is very much like opening the throttle on a car and using the clutch to control the speed (IMHO) :)
 
Paul M said:
Be careful, not all locos speed can be controlled by using the reversing levers. There is a difference in the steam motors, I'll dig out my explanatory bumph if I can find it. My Accucraft locomotives are geared (sorry) up to be controlled by the reverser, but my Roundhouse isn't, it will actually damage the linkages if you do. If you can use the reverser, I find it easier to control, and it will bring the engine to a stop a lot quicker in emergencies
Click to expand...
Thanks for your reply. I have so much to learn and so far have focussed on the Accucraft locos. I should probably delve into some Roundhouse locos also to see how they do things differently.
 
dunnyrail said:
Paul has pretty much hit the nail on the head. For safety you should always close the regulator before changing direction. When loco is stationary regulator should be set so that no steam exits the boiler via the regulator and the forward/reverse set to central ie neither forwards nor backwards.

Some locomotives are likely to crepe forwards or reverse if the regulator is closed but the direction set one way or the other, I have a Roundhouse loco that is very guilty of this.

It should also be noted that most locomotives in our scale do not have a true Walschaerts gear thus ‘notching up’ is not possible, attempts to do so with the gear in part one way or the other will result in lumpy running and as Pauls says could damage the gear.

Exceptions to the rules do exist, Merlin locomotives for example had a regulator/reverse worked from a single RC servo.
Click to expand...
Thank you also, for your thoughts and experience.
 
JimmyB said:
I have a RH loco that as explained by both P Paul M and dunnyrail dunnyrail use the regulator to control speed, and forward/reverse to control direction, however I understand that some Accucraft locos use the Forward/Reverse for both direction and speed. As an engineer this to me is very much like opening the throttle on a car and using the clutch to control the speed (IMHO) :)
Click to expand...
Oh, that last sentence paints a picture! :) Thanks.
 
jblodgett said:
Thanks for your reply. I have so much to learn and so far have focussed on the Accucraft locos. I should probably delve into some Roundhouse locos also to see how they do things differently.
Click to expand...
My Accucraft Caradoc & Lyn use the reverser for speed and direction, but not all Accucraft locos are the same. The obvious thing to do is check the instructions. I would also sy check out the 16mm Association ( 16mm.org.uk) there is a Canadian group, but Canada not being a small country, its probably a bit of a trek for you
 
I used to control speed by using the reverser but after talking to some live steam users with a lot of experience I now use the throttle to control speed as per the design.
This will help you change the Ruby from "outside admission" to "inside admission" so that it will run better forward that in reverse. Option 3

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On the 1:1 steamer I volunteer to fire on when I asked about using the reverser to control speed they said emphatically "No never do that!!!"
 
GAP said:
I used to control speed by using the reverser but after talking to some live steam users with a lot of experience I now use the throttle to control speed as per the design.
This will help you change the Ruby from "outside admission" to "inside admission" so that it will run better forward that in reverse. Option 3

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On the 1:1 steamer I volunteer to fire on when I asked about using the reverser to control speed they said emphatically "No never do that!!!"
Click to expand...
You probably asked the wrong question, next time ask about ‘Notching up with the reverser’ and get an explanation, it is all about efficiency of steam use, not speed.
 
GAP said:
This will help you change the Ruby from "outside admission" to "inside admission" so that it will run better forward that in reverse. Option 3

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Click to expand...
Thanks, yes this is a great article and I already had read it. My Ruby had already be changed to inside admission before I got it from the previous owner.
 
GAP said:
On the 1:1 steamer I volunteer to fire on when I asked about using the reverser to control speed they said emphatically "No never do that!!!"
Click to expand...
In my ignorance on all of this, I might ask if comparing a 1:1 steamer to a model (with simplified setup) is totally valid, but at least this discussion led me to this from Wikipedia:

"The Johnson Bar is effectively part of the entire valve gear, being connected to the various linkages and arms in order to serve its function in adjusting them. This means that the forces in the valve gear can be transmitted to the lever. This is especially the case if the engine has unbalanced slide valves, which have a high operating friction and are subject to steam forces on both sides of the valve. This friction meant that if the Johnson Bar is unlatched while the engine is operating under high steam pressure (wide regulator openings and high cut-off) or at high speeds, the forces that are supposed to act on the slide valves can instead be transmitted back through the linkage to the now-free reversing lever. This will suddenly and violently throw the lever into the full cut-off position, carrying with it the real danger of injury to the driver, damage to the valve gear and triggering wheel slip in the locomotive. The only way to prevent this is to close the regulator and allow the steam pressure in the valve chest to drop. The reversing lever can then be unlatched and set to a new cut-off position and then the regulator could be opened again. During this process the locomotive is not under power."

Not sure this would apply to my Ruby.
 
jblodgett said:
In my ignorance on all of this, I might ask if comparing a 1:1 steamer to a model (with simplified setup) is totally valid, but at least this discussion led me to this from Wikipedia:

"The Johnson Bar is effectively part of the entire valve gear, being connected to the various linkages and arms in order to serve its function in adjusting them. This means that the forces in the valve gear can be transmitted to the lever. This is especially the case if the engine has unbalanced slide valves, which have a high operating friction and are subject to steam forces on both sides of the valve. This friction meant that if the Johnson Bar is unlatched while the engine is operating under high steam pressure (wide regulator openings and high cut-off) or at high speeds, the forces that are supposed to act on the slide valves can instead be transmitted back through the linkage to the now-free reversing lever. This will suddenly and violently throw the lever into the full cut-off position, carrying with it the real danger of injury to the driver, damage to the valve gear and triggering wheel slip in the locomotive. The only way to prevent this is to close the regulator and allow the steam pressure in the valve chest to drop. The reversing lever can then be unlatched and set to a new cut-off position and then the regulator could be opened again. During this process the locomotive is not under power."

Not sure this would apply to my Ruby.
Click to expand...
I wouldn't try it just in case!
 
jblodgett said:
In my ignorance on all of this, I might ask if comparing a 1:1 steamer to a model (with simplified setup) is totally valid, but at least this discussion led me to this from Wikipedia:

"The Johnson Bar is effectively part of the entire valve gear, being connected to the various linkages and arms in order to serve its function in adjusting them. This means that the forces in the valve gear can be transmitted to the lever. This is especially the case if the engine has unbalanced slide valves, which have a high operating friction and are subject to steam forces on both sides of the valve. This friction meant that if the Johnson Bar is unlatched while the engine is operating under high steam pressure (wide regulator openings and high cut-off) or at high speeds, the forces that are supposed to act on the slide valves can instead be transmitted back through the linkage to the now-free reversing lever. This will suddenly and violently throw the lever into the full cut-off position, carrying with it the real danger of injury to the driver, damage to the valve gear and triggering wheel slip in the locomotive. The only way to prevent this is to close the regulator and allow the steam pressure in the valve chest to drop. The reversing lever can then be unlatched and set to a new cut-off position and then the regulator could be opened again. During this process the locomotive is not under power."

Not sure this would apply to my Ruby.
Click to expand...
That all sounds very scary, not sure that Johnson Bar found much favour in UK I can now see why.
 
dunnyrail said:
That all sounds very scary, not sure that Johnson Bar found much favour in UK I can now see why.
Click to expand...
Two Countries, separated by a common language...

Johnson bar and reverser are the same thing.

PhilP
 
jblodgett said:
In my ignorance on all of this, I might ask if comparing a 1:1 steamer to a model (with simplified setup) is totally valid, but at least this discussion led me to this from Wikipedia:

"The Johnson Bar is effectively part of the entire valve gear, being connected to the various linkages and arms in order to serve its function in adjusting them. This means that the forces in the valve gear can be transmitted to the lever. This is especially the case if the engine has unbalanced slide valves, which have a high operating friction and are subject to steam forces on both sides of the valve. This friction meant that if the Johnson Bar is unlatched while the engine is operating under high steam pressure (wide regulator openings and high cut-off) or at high speeds, the forces that are supposed to act on the slide valves can instead be transmitted back through the linkage to the now-free reversing lever. This will suddenly and violently throw the lever into the full cut-off position, carrying with it the real danger of injury to the driver, damage to the valve gear and triggering wheel slip in the locomotive. The only way to prevent this is to close the regulator and allow the steam pressure in the valve chest to drop. The reversing lever can then be unlatched and set to a new cut-off position and then the regulator could be opened again. During this process the locomotive is not under power."

Not sure this would apply to my Ruby.
Click to expand...
In a nut shell, No.
I'm a mainline steam driver/inspector, on our locomotives, I see our reversers as just that, forward/mid-gear/ reverse. I don not believe you can finely control the steam admission to the cylinders by using the reverser.
On a 1 to 1 scale loco you have an indication on the reverser to read off to see what percentage of "cut off" you are using, Cut off is the amount of time that the admission valve is open to steam, ie when starting off in full forward that is 75% cut off and as you gather momentum, you slowly "shorten" the cut off, until (depending on the load and gradient) your running at line/train speed, and the cut off is around 20%. during this the regulator will by opened gradually at first and as most loco regulators have 2 openings (or valves) not going to "full regulator (or "second valve") until the cut off is below 40% cut off, where it will stay unless you need to reduce speed/stop. so as you can see the fine control is done on the reverser.
Now,
If I am moving a loco around on it's own or shunting in a yard/station area, then the loco would be placed in full forward or reverse and controlled by the regulator as you would be just cracking the regulator open for a small amount of steam that is needed, if you where to use the reverser to control the loco, basically, you'd run out of hands!! (imagine trying to put the reverser back to mid gear, braking and shutting the regulator all at the same time!!) .

So, as our model trains are quite light weight in comparison and need to be simple to operate, full forward or full reverse is your simplest choice that the builders give you and the water/gas consumption/ running time is based around that. if you wish to fine tune how you operate your loco, this can be done by how much the gas valve is open, depending on your train weight or gradients.
I hope this helps
 
I had always assumed, as our models valve gear is quite crude, compared to the full-size offering, that the precision of the components, and very fine adjustments to the reverser would preclude 'notching-up' on a model?

PhilP
 
PhilP said:
I had always assumed, as our models valve gear is quite crude, compared to the full-size offering, that the precision of the components, and very fine adjustments to the reverser would preclude 'notching-up' on a model?

PhilP
Click to expand...
Some if the finer builds do have proper working Walschaerts gear, but whether there is any real benefit to notching up in say G1 or G3 would be very debatable.
 
GAP said:
I used to control speed by using the reverser but after talking to some live steam users with a lot of experience I now use the throttle to control speed as per the design.
Click to expand...
The live steam guys have often debated r/c of the throttle and reverser, or just the throttle. Usually, closing the throttle will slow and stop the locomotive gradually. Putting the reverser in neutral will stop it immediately.

My pal with one of the new 13T shays uses the reverser, as it is a geared loco and stopping 'instantly' from low speed is no big deal. On my C-19 2-8-0, it would lock the driving wheels and slide if it had any sort of load when I put it in reverse. But it sure did stop quickly.
My K4 pacific, on the other hand, just has a servo controlling the throttle, and I find that perfectly adequate, as I have no plans for shunting/switching with this engine and its coaches. Shutting the throttle will gradually bring the loco to a smooth stop.
 
I think you need to forget any relationship to a full size loco, the valve gear and regulator are completely different in their use on small scale models. On the Ruby and other Accucraft locos which use the same valve assembly it is usual to set the regulator to provide the maximum speed you require and then the ‘reversing’ valve can be used under radio control to run the loco, the reversing valve acts as both a direction and steam cut off valve.
Full scale loco’s have a completely different method of working as mentioned above, adjustable cut off and regulator are used to balance the power required against the load being pulled and speed obtained, it is a completely different way of working which does not match the loco model you have. You can read all the books you like on the subject but practical experience is the only way to become proficient in the art !
 
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