SD70ACes have 2 inverter grills right behind the cab on the conductors side. Behind those grills, they used to have a vertical grill on a panel. Some units however, were built with a solid panel, but were relaced with a grilled one a few years later. Around the early 2010s, SD70ACes had their vertical grills replaced with a box grill, and any newly produced versions came with this change. What does this grill (and the part its attached to) do, why was it a seemingly required change on every unit, and how did some units work without them?
Max Karl, MRL and BNSF
These were different arrangements for the alternator cooling air. The first two did not have the air go thru inertial filters, the last one you linked has inertial filters with the blower located below in the box. Starting with the GP30, all EMD NA locos had inertially filtered air for traction motors and generators/alternators. To save cost, the SD70ACe was released without filtering that air, eventually it was decided it was needed for the alternator. Compare the size of the inertial filters on SD60's for example to the high mounted one behind the electrical locker on the SD70ACe, the latter are much smaller and only handle the engine air. The lead truck traction motors are ventilated with unfiltered air drawn thru the inverters, IIRC.
Dave
With my tongue firmly in my cheek, I decided there must be a position within the mechanical department of each railroad known as the "Manager of Carbody Filtration". His responsibility was to keep making minor modifications to the external appearance of the fleet to confound the model railroaders. Between new openings, blanking others and moving louvres, he had a broad scope. Additional responsibilities often included relocation of horns and bells.
The best could ensure that after time and evolution very few members of a fleet were 100% identical!
But of course Dave has the real explanation.
John
cx500 With my tongue firmly in my cheek, I decided there must be a position within the mechanical department of each railroad known as the "Manager of Carbody Filtration". His responsibility was to keep making minor modifications to the external appearance of the fleet to confound the model railroaders. Between new openings, blanking others and moving louvres, he had a broad scope. Additional responsibilities often included relocation of horns and bells. The best could ensure that after time and evolution very few members of a fleet were 100% identical! But of course Dave has the real explanation. John
Since the RR's don't have much in the way of mechanical departments doing design work, that position really does reside at the manufacturers. There is nothing the manufacturers would rather do than to freeze the design and keep making the same model over and over again but pesky field problems and customer-driven changes keep making things different, not to mention cost saving ideas, FRA/EPA regs, and technological changes. EMD base budgeted 10,000 engineering hours for any new order, even supposed identical follow-on orders.
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