A great picture of a big Pabst sign and the Chicago skyline, but what’s going on in the lower right corner? A couple of rail cars connected by a cable or hose. Why?
Aren’t those the pneumatic brake lines? Maybe a test or maintenance?
Yes, they are air brake lines. The way railroad brakes is by air in the lines holding the brakes off. When in operation the brakes are held off (indirectly, it’s rather complicated) by line air pressure of about 100psi. The brakes are applied by reducing that line pressure (a valve in the locomotive cab) and the brakes in each car respond by applying in proportion to the reduction in line pressure. If there is no air in the lines the brakes apply and the train doesn’t move. When a locomotive is hooked onto a train, before moving, the air is pumped up by a compressor on the engine. When it reaches a certain point the brakes release and off you go. That does take some time, however. In this case, there are many rows of cars and there is likely a schedule to meet with not enough time to pump up the brakes. Since it’s during the war years (WWII) the locomotives to move the train aren’t there yet to pump the pressure up, so they hook into plant air, which is supplied by large stationary compressors just for that purpose. That way they can set up the train so that when the engine does show up it can hook up and take off.