Different Locomotives Working Together

3639 views
38 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    July 2008
  • 1,599 posts
Posted by rdamon on Thursday, November 19, 2020 6:23 AM

Nice video of a MU separation.

https://youtu.be/6aF3LkCa2V0

  • Member since
    May 2003
  • From: US
  • 19,569 posts
Posted by BaltACD on Thursday, November 19, 2020 7:26 AM

rdamon
Nice video of a MU separation.

https://youtu.be/6aF3LkCa2V0

There are shut off valves for each of the pneumatic hoses that are separating on each engine.  Part of the routine in separating locomotives in addition to disconnecting the 27 pin MU cable that distributes electrical controls among all engines in the consist is to turn all the valves for each of the pneumatic control hoses to the closed position on each of the locomotives at the separation point.

  • Member since
    December 2018
  • 676 posts
Posted by JPS1 on Friday, November 20, 2020 10:17 AM

Here is a somewhat related question:  Yesterday I saw a coal train from my favorite train watching spot.  It appear to have about 120 to 160 cars.  I lost count. 

The train was led by two Dash-9 locomotives; two SD70 locomotives brought up the rear.  Which locomotives provide the air pressure for the train?  

  • Member since
    July 2004
  • 2,442 posts
Posted by Paul Milenkovic on Friday, November 20, 2020 12:57 PM

According to a snarky remark in the last of the Kalmbach Diesel Spotter's Guides that I had seen, all of the running locomotives supply brake line air pressure.

Or at least the GE's do, until they shut themselves down.

If GM "killed the electric car", what am I doing standing next to an EV-1, a half a block from the WSOR tracks?
  • Member since
    December 2017
  • From: I've been everywhere, man
  • 2,882 posts
Posted by SD70Dude on Friday, November 20, 2020 1:13 PM

The lead locomotive and the controlling unit in the remote consist will have their automatic brakes valves cut in, and are the only units directly supplying air to the train.  

Trailing units in each consist provide additional air to the lead unit through the main reservoir equalizing pipe (one of the three MU air hoses found on modern units).  This helps maintain the lead unit's MR air supply if it's compressor cannot keep up. 

Greetings from Alberta

-an Articulate Malcontent

  • Member since
    September 2003
  • 13,894 posts
Posted by Overmod on Friday, November 20, 2020 6:03 PM

Paul Milenkovic
, all of the running locomotives supply brake line air pressure.

You'll get a better picture if you think of each locomotive's air compressor charging that locomotive's main reservoir.  As SD70dude notes, all the main reservoirs in an MUed consist are piped together to act as one with higher volume, and you can  run multiple compressors to get larger volume into the reservoir system.

This assists in charging the trainline in some respects, but not others; as noted, the trainline is charged only through the operating brake valve on each consist, NOT by all the compressor outputs delivering separately.  So the added effect is through less pressure drop from the main reservoir(s), not larger mass flow in parallel to charge the pipe through larger delivery area.

  • Member since
    May 2003
  • From: US
  • 19,569 posts
Posted by BaltACD on Friday, November 20, 2020 7:31 PM

Overmod
 
Paul Milenkovic
, all of the running locomotives supply brake line air pressure. 

You'll get a better picture if you think of each locomotive's air compressor charging that locomotive's main reservoir.  As SD70dude notes, all the main reservoirs in an MUed consist are piped together to act as one with higher volume, and you can  run multiple compressors to get larger volume into the reservoir system. 

This assists in charging the trainline in some respects, but not others; as noted, the trainline is charged only through the operating brake valve on each consist, NOT by all the compressor outputs delivering separately.  So the added effect is through less pressure drop from the main reservoir(s), not larger mass flow in parallel to charge the pipe through larger delivery area.

Despite the combined air pumping and reservoir capacity of the combined locomotive consist - the limiting factor in charging up the air brake system on a train is the amount of air that can be handled through the trainline, which has a internal diameter of apporximately 2 inches - 2 inches to charge all the reservoirs, both service and emergency on all the cars in the train.  The more cars, the more air must be pumped through that 2 inch diameter 'air highway'.

The difference between Main Reservoir Pressure (nominally 130-140 PSI) and train line Feed Valve setting (normally in the 90-110 PSI range) as well as the size of the Main Reservoirs when compared to car reservoirs is intended to keep a steady supply of air moving through the trainline when necessary.

  • Member since
    May 2019
  • 1,366 posts
Posted by Lithonia Operator on Saturday, November 21, 2020 3:55 AM

Let's say that you had two units up front, a mid train engine, and a tail end unit. 2 x 1 x 1

The lead unit suffers a failure, requiring the prime mover to be shut down.

Can you still control the power from the lead unit?

If the lead unit is totally shot, so much so that it can't be used as a "cab car," is the enginee allowed to run from the second unit? If so, would it be required that the conductor ride the dead lead unit, as a lookout?

And if the second unit must be the controller, will this mean someone must walk to the the DP units, to reset something telling them to heed a different master?

  • Member since
    December 2017
  • From: I've been everywhere, man
  • 2,882 posts
Posted by SD70Dude on Saturday, November 21, 2020 8:11 AM

Lithonia Operator

Let's say that you had two units up front, a mid train engine, and a tail end unit. 2 x 1 x 1

The lead unit suffers a failure, requiring the prime mover to be shut down.

Can you still control the power from the lead unit?

Yes.  Until the batteries die.  

Lithonia Operator

If the lead unit is totally shot, so much so that it can't be used as a "cab car," is the enginee allowed to run from the second unit? If so, would it be required that the conductor ride the dead lead unit, as a lookout?

The rules may vary from railroad to railroad.  In my area a member of the crew must be positioned on the leading end to view signals when approaching them, or in non-main track when visibility is restricted from the controlling unit.  

Lithonia Operator

And if the second unit must be the controller, will this mean someone must walk to the the DP units, to reset something telling them to heed a different master?

Yes.  And if your new "leader" is facing backwards, you will have to re-qualify the remotes again after you wye the lead unit later in the trip.

It's a bit simpler on a conventional train, and some EOT's can be armed and tested from the lead unit, others require an employee to go back there and push the button a few times.  

Greetings from Alberta

-an Articulate Malcontent

Join our Community!

Our community is FREE to join. To participate you must either login or register for an account.

Search the Community

Newsletter Sign-Up

By signing up you may also receive occasional reader surveys and special offers from Trains magazine.Please view our privacy policy