I am not concerned here with how the machinery works, but simply with how the driver adjusts the controls in the cab.
So far as I know there are only three different ways to adjust the controls in a Simple Locomotive.
( 1 ) Lever Reverse
Lever Reverse(also known in USA as Johnson bar reverse) is used for:
(a) Manual lever reverse.
(B) Power assisted reverse (steam or air) with miniature Johnson bar control (USA)
Operation:
Reverser has discrete notches.
Driver moves lever forward or backward one notch at time.
The position of the lever corresponds to the cut off.
Represented in OR as for example
Cutoff ( -0.75 0.75 0.0075 0 NumNotches( 15 Notch ( -0.75 0 Dummy ) Notch ( -0.65 0 Dummy ) Notch ( -0.55 0 Dummy ) Notch ( -0.45 0 Dummy ) Notch ( -0.35 0 Dummy ) Notch ( -0.25 0 Dummy ) Notch ( -0.15 0 Dummy ) Notch ( 0.00 0 Dummy ) Notch ( 0.15 0 Dummy ) Notch ( 0.25 0 Dummy ) Notch ( 0.35 0 Dummy ) Notch ( 0.45 0 Dummy ) Notch ( 0.55 0 Dummy ) Notch ( 0.65 0 Dummy ) Notch ( 0.75 0 Dummy ) ) )
This currently works correctly in Open Rails cab views using:
Lever ( Type ( CUTOFF LEVER )
( 2 ) Screw Reverse
Screw reverse is used for:
(a) Manual screw reverse
(B) Power assisted reverse (steam or air) including examples such as "Precision Power Reverser".
Operation:
Reverser is continuously variable.
Driver rotates wheel left or right to adjust cut off.
The actual cut off is shown on a separate indicator scale.
Type ( REVERSER_PLATE GAUGE )
Represented in OR as for example
Cutoff ( -0.55 0.75 0.01 0 NumNotches( 0 ))
This currently works correctly in Open Rails cab views using:
Lever ( Type ( CUTOFF LEVER )
( 3 ) Miniature Lever Reverse
Miniature Lever Reverse is used for steam reverse.
Operation:
Lever has three positions
When lever is in forward position cut off increases slowly.
When lever is in centre position cut off remains constant.
When lever is in backward position cut off reduces slowly.
The actual cut off is shown on a separate indicator scale.
Type ( REVERSER_PLATE GAUGE )
Operation of the lever is not currently possible in OR cab views.
A control called a "Norris Lever" is also mentioned but not explained clearly, this is possibly the same as the miniature Johnson bar mentioned above. Does anyone know more?
Reverser controls on Compounds may be more complex. Possibilities are:
( 4 ) Combined reverser control that gives identical cut off for both HP and LP cylinders.
Operation is the same as ( 1 ) or ( 2 ) above and can be represented in OR in the same way.
Used on Vauclain Compounds.
( 5 ) Separate or Partly separate control for HP and LP valve gear.
On many compounds including those built or modified by André Chapelon then separate controls were provided to operate the HP and LP valve gear.
In some locos both could be moved together to a particular relationship between HP and LP but then one could be adjusted to give some variation to the cut off.
More information and possibly cab views showing how this operated on real locomotives.
This is not currently possible in Open Rails either by cab view or keyboard.
Used on De Glehn / du Bosquet / Chapelon type compounds and also on the original Smith / Wordsell / Johnson compounds.
This arrangement of two seperate reverser controls can not currently be modelled in OR.
( 6 ) Fixed control that gives a pre-determined cut off ratio for HP and LP valve gear.
For example the Deeley rebuilds of the Johnson compounds, Deeley compounds, LMS compounds and GNRI compounds have a screw reverser.
This might be represented as
Cutoff ( (-0.854HP -0.78LP) (0.8875HP 0.83LP) 0.01 0
NumNotches( 0 ))
"Notch" is shown on a separate indicator scale.
Type ( REVERSER_PLATE GAUGE )
The indicator scale has 12 forward and 12 reverse notches shown.
Some actual cut offs corresponding to these are:
Fore 12 HP 88.75% LP 83%
Fore 9 HP 82.1% LP 75%
Fore 6 HP 67% LP 55.5%
Fore 3 HP ? LP 35.5%
Mid F HP 10.6%
Mid LP 15.5%
Mid B HP 13.6%
Back 3 HP 35.4% LP 32%
Back 6 HP 62.7% LP 54.5%
Back 9 HP 77.6% LP 69.5%
Back 12 HP 85.4% LP 78%
This arrangement of different cut offs for HP and LP cylinders controlled by a single control is not currently possible in OR.