Notch terminology

I was talking with a locomotive mechanic recently. I was curious about train operation and the conversation came around to "Engine Notch". He said notch 1 was slow, just off "idle-skip fire". Several times he mensioned the terms "idle skip fire" and "DB skip fire". At the time I didn't think to ask what they actually mean. Can someone shed some light?

eurobill wrote:I was talking with a locomotive mechanic recently. I was curious about train operation and the conversation came around to "Engine Notch". He said notch 1 was slow, just off "idle-skip fire". Several times he mensioned the terms "idle skip fire" and "DB skip fire". At the time I didn't think to ask what they actually mean. Can someone shed some light?

I am not sure about GE or what "Idle skip fire" means but on EMD units the throttle is incremented from Idle to position (notch) 8. Position 1 (Notch 1) is the lowest powered setting where current is delivered to the traction motors. Position 8 (Notch 8) is maximum engine speed and the position where maximum horse power is available.

The word "notch" is from the early Diesels where the throttle was spring loaded and fit into a slot called a notch. I don't know about Steam Engines but I believe a valve controlled steam flow. This may have been notched but I don't know. The only steam engine I crawled on had a valve for the throttle and it was not notched.

I hope this is helps.

I will take a stab that "DB skip-fire" is for Dynamic Brake.

Most large steam locomotives had notches and a spring loaded mechanism to ensure the throttle stayed in one place -- although there were very many notches. Particularly the case with grapevine throttles.

Early diesels did have (in large part) ratcheting escapements in their throttles, designed to prevent rapid opening. You would pull the throttle lever open a notch, and it would not move any farther. When you let go of it, or released your pull, the escapement would trip or release and you could open it another notch. Operation in the other direction, ie to reduce power, was uninhibited. That's where the term "notch" comes from.

The term "skip fire" is curious; he makes it sound as if perhaps modern units with electronic fuel injection aren't injecting fuel to every cylinder on every power stroke when idling.

-Will Davis

Thanks for the input guys. Some other info- the "Skip Fire" is some sort of fuel conservation mode. The mechanic was working on a GE AC4400. The GE "notch" pattern seems to be the same as the EMD you describe- I bet there are some interchange rules that govern this.

eurobill wrote:Thanks for the input guys. Some other info- the "Skip Fire" is some sort of fuel conservation mode. The mechanic was working on a GE AC4400. The GE "notch" pattern seems to be the same as the EMD you describe- I bet there are some interchange rules that govern this.

EMD had a low idle setting that was driven by the oil crisis of the early seventies. It was a combination of Governor "A" valve & "D" valve creating an engine speed lower than the normal idle speed of "No Valve". I do not remember the engine speed of low idle or normal idle..... Sorry...

Typewriters wrote:The term "skip fire" is curious; he makes it sound as if perhaps modern units with electronic fuel injection aren't injecting fuel to every cylinder on every power stroke when idling.

You basically got it right, it is in fact a fuel conversation feature when the engine is idling. If you figure that under normal conditions, every cylinder is firing for every two rotations of the crankshaft, the skip fire feature is firing the minimum number of cylinders necessary to keep the crankshaft turning. This feature when enabled will also draw the engine idle speed way down. Skip fire is only possible on engines with EFI, not on mechanical governor engines. I seem to remember skip fire only on HDL engines (AC6000's), but apparently that feature was cut in on FDL as well. Skip fire was only enabled when the engine was at idle speed and up to optimum operating temperature. In other words, if an engine was too cold, the engine would run at normal idle speed until it warmed up, and then cut over to skip fire. This was basically so that an engine would be "ready for the road" at all times when idling. As soon as you would move the throttle out of idle to notch 1, the engine would come out of the skip fire sequence and fire on all cylinders.