From - Diesel Traction *Manual For Enginemen*; British Transport Commission, 1963
With the exception of a small number of carriages for use in steam charter sets, vacuum brakes aren't used on the UK national rail network any more. The quick-release system seen above was used in diesel multiple units of a certain vintage and was easy and quick to operate, if not explain. If you can remember sitting at the front of a train with the driver seperated from you by a glass partition, then these are the sort of things I'm talking about. Do you remember the big silver handle that made a whooshing noise when the driver moved it? That was the brake handle for the QUICK-RELEASE VACUUM BRAKE FOR DIESEL-MECHANICAL RAILCARS ('C' in Figure 168A).