Train exiting the Tehachapi Loop - GIF

[Drew1966]

I’m pretty sure the freight trains here in Australia use safety brakes where the brakes are applied by reducing the pressure, just like maxi brakes on a semi-trailer.

[Miloslav]

I’m pretty sure the freight trains here in Australia use safety brakes where the brakes are applied by reducing the pressure, just like maxi brakes on a semi-trailer.

Pretty sure you're right. Air pressure keeps the brakes off. If a line breaks the brakes are applied. Westinghouse air brakes

[cjsdad]

I took a few dates to watch trains go through the loop. It's called the Tehachapi Loop but it's actually in Keen. Pretty cool. The trains are not as long now days as they were back when I was a kid. They were miles long back then. They would block traffic at Edison Hwy in Bakersfield for half an hour it seemed like.

[Crusty]

The air brakes on trains (and trucks) are operated by pressure pots which are spring loaded with very strong springs to always apply the brakes. In the pots are two diaphragms that communicate with the air systems - one system in which pressure is applied to compress the spring for normal operation and variably bled off to apply variable braking, and the other functions as part of the emergency system so that if primary air pressure is lost the spring applies full braking. Those springs are bad enough that it's a somewhat tense operation in a shop to disassemble one to change the diaphragms.

[Frank S]

The air brakes on trains (and trucks) are operated by pressure pots which are spring loaded with very strong springs to always apply the brakes. In the pots are two diaphragms that communicate with the air systems - one system in which pressure is applied to compress the spring for normal operation and variably bled off to apply variable braking, and the other functions as part of the emergency system so that if primary air pressure is lost the spring applies full braking. Those springs are bad enough that it's a somewhat tense operation in a shop to disassemble one to change the diaphragms.

I don't know about trains but in the trucking industry those brake chambers on the emergency side for about the past 2 decades are no longer rebuild able due to the safety issues that is why new ones were at one time federally subsidized to keep replacement costs down. Used to the 2 chambers were held together with the same type of clamp. When a diaphragm went bad in the service side you just removed the clamp and installed a new one. Too many drivers tried to replace them on their own without knowing which side to remove and were badly injured or killed causing a regulation to mandate the change in the way the chambers were made. You can still replace the diaphragm on the service side by doing what is called caging the spring using a toggle bolt that comes on every new assembly but few ever do this any more since it is cheaper to just replace the whole thing.

[Crusty]

You can tell it's been a while since I've done one and I guess it's another sign that I've become outdated. My newest truck was a 1980 model. Most drivers these days don't even know how to adjust their trailer brakes.

[Frank S]

You can tell it's been a while since I've done one and I guess it's another sign that I've become outdated. My newest truck was a 1980 model. Most drivers these days don't even know how to adjust their trailer brakes.

Yep and since the DOT requirement of automatic slack adjusters was mandated you never know what size wrench you need to adjust them any more used to be every driver had a 9/16" combination wrench handy Now days it can be anything from a 5/16" 3/8 9/16" or even a square head on the adjustment.
And I think it was 98 when the antilock systems was re mandated But to be fair it has been a slight improvement over the old 721 antilock system. But still a PITA to keep functioning properly and don't get caught without the blue antilock indicator light burning on the left rear corner of your trailer. Some states take it real seriously.

[Crusty]

That's all news to me.

I always liked to pull someone else's trailer because they were responsible for brake maintenance on their equipment and I saved my tractor brakes by often using the trailer brakes, so consequently they needed periodic adjustment.