"high Vacuum " pipe and associated reservoirs and valves were used as a means to increase the speed of the release of the brake. The vacuum exhausters on these units were mechanically driven by the engine; as the engine would normally only be idling when a brake release was required, release would have been extremely slow if the conventional single-pipe system had been employed. This problem did not occur on BR's diesel locomotives, as their exhausters were electrically driven, and so could be run at high speed to release the brake irrespective of engine speed. Present-day use of vacuum brakes Today's largest operators of trains equipped with vacuum brakes are the Indian Railways and Spoornet (South Africa), however there are also trains with air brakes and dual brakes in use. South African Railways (Spoornet) operates more than 1 000 electric multiple unit cars, which are fitted with air compressed brakes. The electro-vacuum system uses a train pipe and basic automatic vacuum brake system, with the addition of electrically controlled application and release valves in each vehicle. The application and release valves greatly increase the rate of train pipe vacuum destruction and creation. This, in turn, greatly increases the speed of brake application and release. The performance of electro-vacuum brakes on SAR EMUs is equivalent to electro-pneumatic braked EMUs of a similar age. Other African railways are believed to continue to use the vacuum brake. Other operators of vacuum brakes are narrow-gauge railways in Europe, the largest of which is the Rhaetian Railway. Vacuum brakes have been entirely superseded on the National Rail system in the UK (with the British Rail Class 121 "bubble cars" being the last mainline trains to have vacuum brakes-they finished service in 2017), although they are still in use on most standard gauge heritage railways. They are also to be found on a diminishing number of main line vintage special trains. Iarnród Éireann (the national rail operator in the Republic of Ireland) ran vacuum-braked British Railways Mark 2 stock on passenger trains until the end of March 2008 and still operates vacuum-braked revenue freight (at least in the case of Tara Mines ore traffic). All mainline heritage trains are run with vacuum brakes – the whole of Iarnród Éireann's current locomotive fleet has both air and vacuum train brakes fitted. The Isle of Man Railway uses vacuum brakes fitted to all its coaching and wagon stock,