On trains, there is only one black brake line, so I'm sure they work differently. Keith?
Well, I finally got a few minutes to reply.....
On a long train, say 130+ cars it can take up to an hour or more to fully charge the "train line", the black hose that runs from car to car.
The train's brakes are the invention of Mr. Westinghouse and haven't changed drastically in a hundred years.
Each car has two air tanks, a service and an emergency reservoir.
All cars' brake reservoirs are connected to the train line via a three way valve. Let's say you put together a train in the yard and it has no air on it at all.
It has no brakes at all either except the hand brakes that must be applied individually by a person turning a wheel.
All the cars' hoses are connected and the train line hooked to the locomotive.
The compressor on the loco begins to "charge the line", it has to fill all those reservoirs to 90 psi. There are usually quite a few leaks to overcome as well. The cars are in many various states of repair, being leased by god knows who. Once the entire train is charged to 90psi, the brakes are still released, but ready for use. Now the train line acts as not only the supply, but as the application device as well. The brake lever in the cab actualy lets air out of the line via a valve and reduces the train line pressure. The three way valve on each car recognizes the reduction, and releases some of the air in it's service reservoir into a actuating cylinder which, through a series of mechanical levers applies pressure to the brake arm attached to the shoes and the shoes to the tread of the wheel. The more you lower the pressure on the train line, the harder the brakes are applied. To release the brakes, close the brake valve in the cab and the train line pressure begins to build again. The three way valve senses the rising pressure and dumps the pressure out of the actuating cylinder and starts to re-charge the reservoirs as well. The application of the brakes is progressive from the front to the rear of the train as the pressure lowers, and releases the same as the pressure rises. There are a couple of manufacturers that have started using Electronic Control Pneumatic (ECP) brakes. These have a shall electrical connection between the cars that triggers all the car's brakes to come on and release simultaneously. The effect on an empty train's stopping dostance can be as much as 40% shorter. Like magnetos on a plane, they have to work in the event of an electrical fault just like the normal brakes do. The loco has an independent brake, a hand brake to park the loco and dynamic brakes which turn the traction motors into big generators across which huge resistor grids are shorted in varying degrees to make electric brakes out of them.
When a train is parked and the engine shut off, the train line will leak down in a few hours, leaving the thing capable of rolling away. There are rules rtegarding how many hand brakes need to be set for any gven train on any given grade. It's a real PITA to let a train leak down and recharge it also because there are federally mandates pre-trip tests that have to be performed if the train line go to 0 psi.
This is a pretty simplified version, but you get the idea.
For all you ever wanted to know, see the attached Word document.
It's the best document Iv'e seen on the subject.