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(last edited July 20, 2005) Front Page | Recent Changes | Title Index | User Preferences | Random Page | HelpThe main disadvantage of a train braking system using an air pipe to control the brakes is the propagation time - the time taken for a change in pressure to reach all the vehicles. The longer the train, the greater is this time. Some long US freight trains may take as long as 15 minutes to recharge a completely airless brake system. Even on a short train, with a fully charged brake system, it may take several seconds for the rear vehicle to respond to changes in brake pipe pressure.
One way of reducing the recharge time and getting a quicker release of brakes is to use a second pipe. The second pipe is the main reservoir pipe, which is recharged directly from the compressor. It is constantly kept at full pressure, regardless of the status of the brake pipe pressure. When brake release is selected, the distributors on each vehicle use this main reservoir air to recharge the auxiliary reservoirs instead of using brake pipe air as on the one pipe system. During an application, some systems add main reservoir air to the brake cylinders to speed up operation.
The two-pipe systems is also a feature of some electro-pneumatic brake systems.
