20th century, many British railways employed vacuum brakes rather than the railway air brakes used in much of the rest of the world. The main advantage of vacuum was that the vacuum can be created by a steam ejector with no moving parts (and which could be powered by the steam of a steam locomotive), whereas an air brake system requires a noisy and complicated compressor. However, air brakes can be made much more effective than vacuum brakes for a given size of brake cylinder. An air brake compressor is usually capable of generating a pressure of vs only for vacuum. With a vacuum system, the maximum pressure differential is atmospheric pressure ( at sea level, less at altitude). Therefore, an air brake system can use a much smaller brake cylinder than a vacuum system to generate the same braking force. This advantage of air brakes increases at high altitude, e.g. Peru and Switzerland where today vacuum brakes are used by secondary railways. The much higher effectiveness of air brakes and the demise of the steam locomotive have seen the air brake become ubiquitous; however, vacuum braking is still in use in India, Argentina and South Africa, but this will be declining in near future. See Jane's World Railways. Visual differences between the two systems are shown by air brakes working off high pressure, with the air hoses at the ends of rolling stock having a small diameter; vacuum brakes work off low pressure, and the hoses at the ends of rolling stock are of a larger diameter. Air brakes at the outermost vehicles of a train are turned off using a tap. Vacuum brakes at the outermost vehicles of a train are sealed by fixed plugs ("dummies") onto which the open end of the vacuum pipe is placed. It is sealed against a rubber washer by the vacuum, with a pin to hold the pipe in place when the vacuum drops during braking. Air brake enhancements One enhancement of the automatic air brake is to have a second air hose (the main reservoir or main line) along the train to recharge the air reservoirs on each wagon. This air pressure can also be used to operate loading and unloading doors on wheat wagons and coal and ballast wagons. On passenger coaches, the main reservoir pipe is also used to supply air to operate doors and air suspension. Electropneumatic brakes