Rick , to answer your question : Generally you do not have to "bail" the independent air if you have the brake handle in the "release" position(The "holding" position will retain the locomotive airbrakes), but engineers bail off the independent compulsively as this is a good habit to get into. Though the No.6 stand(what K-class engines have)is designed to automatically set engine brakes when an application is made ,it supposed to release them only in the "release" position , so bailing off the tender brake or retaining it is the engineers discretion , depending on how much braking power he needs .
No.6 brake stands have a maze of tiny passages cast in them and some dirt could cause the engine brakes to set even in the "release" position . In the 1940s the larger mainline engines (K-28s ,K-36s ,K-37s)had the "e-t" feature added , which eliminated the need for a triple valve and retainer on the engine A different triple valve (distributing valve) was mounted under the cab ..Part of the new feature was the "mountain cock" which allowed the engineer to cut in or cut out the driver brakes . Driver brakes were used mainly in switching ,running light ,and to assist in controlling short ,heavy trains .The engine brakes are not supposed to be used in downhill running with a train ,and are supposed to be cut out . It is believed that using the driver brake rigidizes the drivers ,and some believe this may have caused some derailments .I have used the engine brake with hard-to-control trains , but only in straightaways ,cutting them out with the mountain cock on curves , that naturally slow a train down anyway . Experienced engineers cut the driver brakes in when spotting a train at a water tank or platform . Hope that is an intelligible answer .
