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(last edited July 20, 2005) Front Page | Recent Changes | Title Index | User Preferences | Random Page | HelpA manually operated valve mounted on many US freight cars to provide a constant minimum application even though the brake has been released from the driver's brake valve in the cab. Normally, when brakes are released, all of the air in the brake cylinders is discharged to the atmosphere. By setting retainer valves, when the brakes are released, some of the air pressure is "retained", hence the name. If set for say 10 psi, the brake cylinder pressure will not drop below 10 psi until the retainer is reset (or until the air eventually seeps out). Typically, a certain number of cars on the rear of the train would have their retainers set by the conductor. Rulebooks indicate how many retainers to set before descending.
There are 2 types of retainer valves, a 3 position type and a 4 position type.
The operating positions are:
EX- Exhaust, normal will not retain air
HP-High Pressure, will retain 20psi
SD-Slow Direct Exhaust, will not retain air but will exhaust the air more slowly then normal
LP-Low Pressure, will retain 10psi, only available on the 4 position retainer valve.
If you make a stop on a grade and have to release the air brakes to recharge the system, then before you release the air brakes you must apply a sufficient number of hand brakes to secure the train if you are not sure the locomotive brakes will hold the train. Depending on conditions, that may mean every hand brake on the train. (I know I would not want to be the conductor who had to set 100 hand brakes.) After that job is completed then the air brakes can be released and the system may be recharged. If you do attempt to use the locomotive brakes to hold the train and it turns out that they are not sufficient to hold the train you may not have enough air left to stop the train again.
Written with newsgroup contributions from David Gianna and Donald Reventlow.
