Monday, 16 April 2012

General Motors EMD Locomotive Controls

General Motors EMD Locomotive Controls

General Motors EMD Locomotive Controls of Sri Lankan Locomotives
Class M2 loco logo

Gyan Fernando

Of the locomotives of the Sri Lankan Railway, two types of locomotives have a General Motors EMD pedigree.
The Class M General Motors EMD G12 locomotives of Sri Lanka and the Henschel built Class M6 locomotives have General Motors EMD type controls.

The Class M2 locomotives are pure GM EMD and are designated as G12 by EMD.
The Class M6, although built by Thyssen Henschel of West Germany, have EMD prime movers and EMD controls. This of course makes these two classes similar in some ways.
(use link to read more)

Controls on GM EMD G12 loco No 626 Montreal
Control levers on Class M2c No 626 Montreal
The main three controls are the Reverser, the Throttle and the Dynamic Brake lever or Selector

Locomotive reverser
The Reverser
The Reverser
This is the lowermost of the three controls. Although traditionally referred to as the “Reverser”, this lever has three positions: Forward, Reverse and Neutral, with Neutral being the middle position.

The Reverser handle is removable and the driver (engineer) is expected to remove it whenever he leaves the cab. 

The Throttle
locomotive throttle
The Throttle
The Throttle lever is placed above the Reverser and has nine positions if the “Idle” position is included or eight driving positions otherwise.
Each position is known as a “notch” and the lever is advanced through the notches in a stepped fashion (i.e. not in a smooth fashion.)
The engineer has to advance the throttle one notch at a time to prevent strain on the engine and possible ensuing damage. For example, he cannot move the handle from notch one to four without going through notches two and three.

Putting the throttle into Notch 1 engages a set of contactors (massive electrical relays). These contactors link the main generator to the traction motors. Each notch engages a different combination of contactors, producing different amperages. 

The traction motors produce more tractive power at higher amperages.

Some combinations of contactors put certain parts of the generator winding into a series configuration that results in a higher amperage. Others put certain parts in parallel, resulting in a lower output.

The Diesel engine also needs to “rev up” with each notch and this is achieved by means of further relays that adjust the fuel injectors.

The Selector
This is the topmost handle and movement of this selects either the throttle or the dynamic brake, with the position being indicated in the selector window. When the selector is in the “Throttle Position”, advancing the throttle causes power to be applied and the locomotive moves off.

When the selector is in the “Dynamic Brake” position, advancing the Throttle lever increases dynamic braking effort.

This type of selector arrangement is seen in Class M2 (GM EMD G12) locomotives, whereas in the Class M6 Henschel locomotives the arrangement is slightly different. 

Locomotive controls on Henschel Class M6 Sri Lankan
Control levers on a Class M6 Henschel locomotive

Differences in the Class M6 Controls
The Class M6 controls consist of the Reverser and the Throttle as above, but instead of a Selector, the topmost lever is the Dynamic Brake handle.
Advancing this handle, results in the dynamic brake effort increasing. It cannot however be advanced unless the Throttle is in the “idle” position.

The various levers are interconnected by an interlocking mechanism which prevents inappropriate use of controls.

For example, the Reverser cannot be moved when the locomotive is moving under power. To move the Reverser the Throttle has to be moved to "Idle" first.
 With dynamic braking, the throttle has to be brought to the idle position before the Dynamic Brake lever can be moved.
As mentioned above, in the case of the dynamic brake, the lever cannot be advanced when the locomotive is under power. In addition there is also a need to wait 10 seconds in idle throttle setting before applying the dynamic brake. This latter warning is clearly displayed on the control panel.

Other controls
Other significant controls on the control panel itself are the Alerter and the Sander control. The brakes are separately located.

Control Panel on GM EMD G12 Class M2c Montreal
Control Panel on GM EMD G12 Class M2c Montreal
The Author at the controls of Class M6 No 797

A note about the photographs: For obvious reasons none of the photos above show the Reverser handle in situ. The Engineers, quite prudently, removed it before I entered the cab!

Picture credits: The photographs all belong to the author. The two line drawings are from the EMD Engine Manuals and are copyright free.

2 EMD GP-9 operation: Although this deals with the GP-9, the controls are similar.  The Unofficial CQPA Web Site // EMD GP-9 Operators Manual


  1. great work. gave me lot of knowledge. thank you

  2. This is great Gayan. Very informative indeed. What about the Brush built M7s, with their EMD engines, do they have similar controls?