What operational advantage did the vacuum brake system possess over the standard Westinghouse compressed air system regarding brake release?

Answer

Graduable release.

The vacuum brake offered the advantage of graduable release, meaning the driver could restore some vacuum to partially release the brakes. This contrasted with the emerging compressed air system's ability to be 'lapped' for constant application.

What operational advantage did the vacuum brake system possess over the standard Westinghouse compressed air system regarding brake release?
inventioninventorvacuum