When is a multi-engine pull necessary?

Every railroad has tonnage ratings for its locomotives.  It's all computerized now, but, when they used to publish them in the employee timetable or Superintendent's Bulletins, there would be a vertical column for each class of locomotive, and a horizontal column for each Subdivision (or part of a Subdivision sometimes).  The tonnage rating for that class of locomotive on that territory was listed where the two columns intersected.

That's the maximum tonnage that a locomotive can pull on that territory without exceeding the traction motor continuous rating on DC units.  AC units don't have short time ratings and measure things differently.  So, . . .

. . . nowadays they use horsepower per ton.  On level or undulating territory, 1.5 hp/ton can lug a string of empties along if speed is not important.  2.5 hp/t can move a non-priority train.  A medium priority train requires 3.0 hp/t or more, and a hot train needs 4.5 hp/t.  On mountain grade territory, the numbers are higher.  These calculations are not only for protection of the traction motors, but also for the horsepower needed to make the kind of speed required by the various priority classes.  And the reason above all others is fuel consumption.  The different services have to be priced with fuel as a factor.  It takes more fuel to run the same tonnage fast instead of dragging it along.

Often when you see too much power at the head end it's for the same reason you see empty cars in trains: deadheading of equipment is inevitable. Coal trains out of the Powder River Basin need all that power but those same trains heading West empty are ridiculously overpowered.

Helpers/pushers is a classic method of minimizing imbalances of power. The B&O mainline East from Pittsburgh to Sand Patch is gentle and long whereas the grade West from Cumberland to Sand Patch is short and steep. Much more power is required on Westbound trains than on Eastbounds. In order to avoid more power than needed in Eastbounds Pushers are employed out of Cumberland to the summit.

Lew

geysergazer posted:

Often when you see too much power at the head end it's for the same reason you see empty cars in trains: deadheading of equipment is inevitable. Coal trains out of the Powder River Basin need all that power but those same trains heading West empty are ridiculously overpowered.

Helpers/pushers is a classic method of minimizing imbalances of power. The B&O mainline East from Pittsburgh to Sand Patch is gentle and long whereas the grade West from Cumberland to Sand Patch is short and steep. Much more power is required on Westbound trains than on Eastbounds. In order to avoid more power than needed in Eastbounds Pushers are employed out of Cumberland to the summit.

Lew

In the case of coal empties heading back to the mine, the same locomotive consists which hauled them when loaded, often are left in place to return them empty to the mines.  Horsepower per ton is managed by isolating* some locomotives in each consist.  Remember, it's the fuel that drives this.  Coal empties are scheduled to arrive at the mine so that they do not need all the horsepower that the loads did, and engine crews are required to isolate some units in each consist, to adjust hp/t to the specified ratio before departing the utility plant with the empty train.  So, remember that horsepower per ton is calculated by dividing the combined horsepower of all operating locomotives (including helpers, pushers, or Distributed Power units) by the weight of the train in tons (including the weight of isolated locomotives in the engine consist[s]).  Therefore, don't be fooled by the appearance of a certain number of locomotive units.  It's only the operating ones that count toward the horsepower.

*  On each diesel-electric locomotive, there is a switch on the engine control panel on the rear cab wall, which typically has two positions, RUN and ISOLATE.  When the switch is in the RUN position, the locomotive responds to throttle commands, regardless of its position in the consist.  When in ISOLATE, the locomotive will simply idle continuously, or, if equipped with fuel saving equipment, will automatically shut down its engine for periods, re-starting it periodically, to maintain the water and oil temperatures, and keep the batteries charged, as required.

Tom, thanks for that info. I have assumed that in the age of 13,000HP head ends unneeded power is left on idle but it's nice to get the actual dope.

Lew

Some SP units at one time had something where the engineer could put as many units in the lead as needed to load  I think the equipment was called "select a power".  Can this be done today?

Dominic, your memory has served you well.  Yes, there was equipment called Select-A-Power.  SP, Santa Fe and KCS all had some locomotives equipped with it.  It relied on the Engineer to select 1,2,3, or 4 units on-line.  Locomotive diesel engines of the EMD Dash-2 and GE Dash-7 era were most fuel-efficient at, or near their maximum RPM.  Therefore, where the terrain allowed, a train could be pulled by three units in Run 7 and Run 8, just as fast as by four units in Run 4 to Run 6, using less fuel.

Select-A=Power did not last, because

1. The engine consist had to use the specially-equipped units.  Non-equipped units could be m-ued in the consist, but would not respond to the selector buttons.  Additionally, Mechanical forces had to set up individual units as Number 1, 2, 3, or 4, so they would be isolated in reverse order when the Engineer requested fewer units.  All this cherry picking took time and extra hostling.
2. Instructing Engineers to do things they don't want to do is like herding cats.  Engineers did not like the idea of isolating trailing units instead of reducing throttle, because, when they wanted full horsepower again, they could get it quickly by just increasing the throttle position when running conventionally, but it took time for Select-A-Power to place an engine on-line, and for the engine to gradually build up engine RPM and traction motor amperage.  Therefore, Select-A=Power was used reluctantly, and very sparingly.

Select-A-Power quietly faded away.  Today's locomotive consists do the same thing, automatically, and it's done with upgraded software instead of lots of wiring and control buttons.

I'm so glad I brought this up because I am learning a great deal about railroad operations, especially from a multi engine point of view.  Thanks for all the great information.  I had no idea, I mean, no clue that it took all of this to run two or more locomotives. 

Number 90 posted:

Dominic, your memory has served you well.  Yes, there was equipment called Select-A-Power.  SP, Santa Fe and KCS all had some locomotives equipped with it.  It relied on the Engineer to select 1,2,3, or 4 units on-line.  Locomotive diesel engines of the EMD Dash-2 and GE Dash-7 era were most fuel-efficient at, or near their maximum RPM.  Therefore, where the terrain allowed, a train could be pulled by three units in Run 7 and Run 8, just as fast as by four units in Run 4 to Run 6, using less fuel.

Select-A=Power did not last, because

1. The engine consist had to use the specially-equipped units.  Non-equipped units could be m-ued in the consist, but would not respond to the selector buttons.  Additionally, Mechanical forces had to set up individual units as Number 1, 2, 3, or 4, so they would be isolated in reverse order when the Engineer requested fewer units.  All this cherry picking took time and extra hostling.
2. Instructing Engineers to do things they don't want to do is like herding cats.  Engineers did not like the idea of isolating trailing units instead of reducing throttle, because, when they wanted full horsepower again, they could get it quickly by just increasing the throttle position when running conventionally, but it took time for Select-A-Power to place an engine on-line, and for the engine to gradually build up engine RPM and traction motor amperage.  Therefore, Select-A=Power was used reluctantly, and very sparingly.

Select-A-Power quietly faded away.  Today's locomotive consists do the same thing, automatically, and it's done with upgraded software instead of lots of wiring and control buttons.

Conrail was big with Select-a-Power.

Where I live we have a three times weekly coal delivery to the local power plant. Around 100 cars per trip. That delivery is complicated by a couple factors. First, there is a pretty stiff grade going down into the river valley where the plant is located. Then when they get to the bottom, they have to throw the switch, and go in a mile off the main.

They always have three units on the front, and a couple on the back. I think they even use two crews for this, so the train is never backing up. The back end power gets cut off when they arrive at the plant, and they switch out the empties and leave the loads. Then they put the rear units back on and reverse the process. Once back out on the main, the rear units lead the way home to the yard.

Number 90 posted:

Dominic, your memory has served you well.  Yes, there was equipment called Select-A-Power.  SP, Santa Fe and KCS all had some locomotives equipped with it.  It relied on the Engineer to select 1,2,3, or 4 units on-line.  Locomotive diesel engines of the EMD Dash-2 and GE Dash-7 era were most fuel-efficient at, or near their maximum RPM.  Therefore, where the terrain allowed, a train could be pulled by three units in Run 7 and Run 8, just as fast as by four units in Run 4 to Run 6, using less fuel.

Select-A=Power did not last, because

1. The engine consist had to use the specially-equipped units.  Non-equipped units could be m-ued in the consist, but would not respond to the selector buttons.  Additionally, Mechanical forces had to set up individual units as Number 1, 2, 3, or 4, so they would be isolated in reverse order when the Engineer requested fewer units.  All this cherry picking took time and extra hostling.
2. Instructing Engineers to do things they don't want to do is like herding cats.  Engineers did not like the idea of isolating trailing units instead of reducing throttle, because, when they wanted full horsepower again, they could get it quickly by just increasing the throttle position when running conventionally, but it took time for Select-A-Power to place an engine on-line, and for the engine to gradually build up engine RPM and traction motor amperage.  Therefore, Select-A=Power was used reluctantly, and very sparingly.

Select-A-Power quietly faded away.  Today's locomotive consists do the same thing, automatically, and it's done with upgraded software instead of lots of wiring and control buttons.

Tom 

With item two on your list. could the Select-A-Power train stall if the units didn't ramp up fast enough? Or if the engineer didn't anticipate the upcoming grade? Or was there an override to jump the power up?

Very informative thread. Explains a lot. I'm guessing that UP's extensive use of Gensets on their locals further optimizes horsepower utilization and fuel economy.

CSX FAN posted:

Number 90 posted:

. . . Select-A=Power did not last, because

1. The engine consist had to use the specially-equipped units.  Non-equipped units could be m-ued in the consist, but would not respond to the selector buttons.  Additionally, Mechanical forces had to set up individual units as Number 1, 2, 3, or 4, so they would be isolated in reverse order when the Engineer requested fewer units.  All this cherry picking took time and extra hostling.
2. Instructing Engineers to do things they don't want to do is like herding cats.  Engineers did not like the idea of isolating trailing units instead of reducing throttle, because, when they wanted full horsepower again, they could get it quickly by just increasing the throttle position when running conventionally, but it took time for Select-A-Power to place an engine on-line, and for the engine to gradually build up engine RPM and traction motor amperage.  Therefore, Select-A=Power was used reluctantly, and very sparingly.

Select-A-Power quietly faded away.  Today's locomotive consists do the same thing, automatically, and it's done with upgraded software instead of lots of wiring and control buttons.

Tom 

With item two on your list. could the Select-A-Power train stall if the units didn't ramp up fast enough? Or if the engineer didn't anticipate the upcoming grade? Or was there an override to jump the power up?

There was no danger of stalling.  There should not have been enough units isolated at any time to cause the train to stall, and the Engineer would have used Select-A-Power to put any isolated engines on-line before beginning to ascend a grade where he knew the train would want to slow down.  Anticipation (by knowing the physical characteristics of the territory and the type of locomotives in the consist, and the length and weight of the train is an important factor in being a good Locomotive Engineer.