The brakes on a train operate by air pressure. But the air pressure is not used in the way it was originally intended. It's used exactly the opposite way. You see, the first air brakes on trains were designed to operate as follows: Someone who wanted to stop the train would pull a certain lever, air pressure would trigger the brakes, and the train would stop. Problem was, the hoses that were used to channel this pressurized air were made of rubber, which erodes, wears out, and can be delectable to certain rodents. As holes developed in the rubber hoses, when the air brakes were triggered . . . well, you can probably figure out the unsatisfactory result.
The solution to this alarming problem was to reverse the thinking that produced air brakes in the first place. The improved method of stopping trains still used air pressure, but the air pressure was used to keep the brakes off. To stop the train, instead of using pressurized air to close the brakes, air was released to close the brakes. A 180° solution, if ever I saw one.
Oh, by the way, they still used the same type of rubber hoses to channel the air, but now if the rubber is compromised in any way, the brakes simply activate and stop the train. Yes, this could be a problem to deal with. But nowhere near as serious a problem as having no brakes when you need them.
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