06-29-2010, 05:44 PM
Gary S Wrote:If we are switching out industries, what is the process used when cars are coupled onto the train?
Gary, my understanding is
a. Would we connect the air hoses and pump up the system for every move no matter how short?
No, during shunting the hoses are not connected if the break force of the engine only is sufficient for the weight, speed and may be downward hill/gravity and possible wind/storm
b. Is it correct that the brakes are released only when air is in the system?
No, the breaks release also when all air is out of the system
c. Would we ever keep the air in a car's brake system to keep the brakes released even though not connected to a loco?
No, you keep the air in the system to hold the car/cut. Additionally the manual break must be applied (refer to b). But you have to connect the hose and pump more air into the system to release the breaks again to get the car/cut going.
This http://www.railroad.net/articles/railfan.../index.php is a nice introduction.
The basic idea is a clever valve in each car that presses the break shoes against the wheels if the pressure is below a certain limit. If that threshold is reached the breaks are released.
The engineer pumps air (to be above the threshold) into the system to release the breaks and reduces the pressure (below the threshold) to apply the breaks. That ensures the breaks will be applied when the train is separated. Of course the break is also released when ALL air is out of the system (refer to b).
In electric terms:
Each car has a rechargeable battery of 12Volt. That battery operates the brakes. There is a single cable coming from the engine to all cars. Then the cable has a voltage higher than 12 Volt the breaks are released and the battery is recharged. To apply the breaks softly you reduce the voltage to 11 Volt. To break harder you reduce it to 8 Volt. In case of emergency you ground the line and send 0 Volt. The breaks will be fully applied from the battery. That hold true until the battery is empty. You have than a car without an operational break. It is therefor essential to have some periods of recharge to keep the system operational.
Reinhard