The DPU Update column in last month's issue of CROSSROADS caused interest in more ways than one with its information contents; it produced questions from two different angles, some were my on as follow-up material for this month's feature, along with from you, the readers who have been closely involved with DPU train operations.
This correspondent would like to thank you for your continued support, in whatever form it might take shape, with providing a better understanding in this expanding area of train operations.
As always, should you have anything (a question, a personal experience, etc.) that may be of benefit to the readers, contact the CROSSROADS office at (817) 878-4528, or by the E-Mail addresses of Eduardo M. Derrick or Jay C. Martin.
Light Axle Coal Trains: More Background -- The topic which garnered the largest interest was regarding the format called the light axle DPU coal trains; these are the jobs which use as their power format a pair of AC Traction units for the lead consist, and a C40-8 DC unit as the lone remote.
The main question was why isn't the DC unit used in the lead portion and the AC model in the remote position. As part of this determination, there were three test trains which came into Texas which assisted in making this decision. One item they discovered was that having a DC unit as the point leader of the lead consist would not have been of that great an aid.
But the most significant advantages came when they operated a train with the current format; an all AC unit lead consist could provide greater flexibility with train handling, particularly with their low speed adhesion capabilities, than what could be done with an AC-DC mixed consist.
Although they have this higher continuous tractive effort ability at low speeds, the two AC units should not produce coupler stresses which would exceed 370,000 lbs., which is the rating for the high tensile couplers which are used on coal cars.
System Screen IBA Loop Error Message -- Along with my experiencing this during a training trip for another engineer, there have also been questions asked to me about a message display in the SYSTEM screen called IBA LOOP ERROR.
The IBA stands for independent brake application. As other information, you might also find another message in that log called ER LOOP ERROR: ER stands for equalizing reservoir.
Both of these are messages describing the LOCOTROL III system's way of measuring reactions to those pressures. The measurements are made with the LOCOTROL equipment; on an E-Brake equipped locomotive, it is based on data that is sent over to LOCOTROL that indicates these air pressures.
These are necessary on locomotives equipped with the 26L air brake, where LOCOTROL actually controls the equalizing reservoir and brake cylinder pressures in response to brake applications.
On an E-Brake equipped unit, it actually is redundant to the E-Brake, which also has its own fault code sensing for independent, equalizing reservoir, and any other kind of brake pressures. So unless you receive a fault code along with this message, it does not reflect the presence of anything serious with the air brake system.
C40-8 Unit No. 9313: The Pushbuttons Application -- I have been known to find interesting pieces of equipment aboard locomotives; one them I reported on last month was on a DPU equipped C40-8 DC unit No. 9313, which had above the rear headlight switch a small pushbutton panel for provision of independent braking control separate from the regular handle on the E-Brake control unit.
My own question about this was whether this was some type of a test application. The answer is: Not really. This, however, was done to the last 12 or 13 standard cab C40-8 units which went thru the E-Brake and DPU retrofit program done at the facilities in Elko, Nevada.
It was done in order to make an E-Brake equipped unit have the flexibility of lead consist only independent braking control during DPU operations as is what the pneumatic brake units can provide.
There may not be many opportunities to try this as the C40-8s will be used mostly as the remote consist leaders, but who knows; the possibility for you to try this out by chance in the future if one is a leader could occur.
IDP Update -- There has been more developmental work going on with the IDP system, with the more recent activity taking place at the AAR-TTC in Pueblo, Colorado.
The locomotives involved with this latest episode were UP C44AC unit No. 6804 and EMD pre-production SD80MAC unit No. 8000.. A key item to note in the meantime: The SD90MAC locomotives at this time are not equipped with the Distributed Power system.
Although it is possible to draw up this particular selection on the EM2000 LSI display, the feature is not available. This is not to say that they cannot be used as the trailing locomotive to a DPU equipped unit, as recently thru Fort Worth, SD90MAC No. 8006 was the second out unit in the lead consist on DPU coal train CROHS-16.
This month's edition of UPDATE is another in a series on the latest information I have received since the last issue of CROSSROADS.
Marcel is a Fort Worth based locomotive engineer