American and continental European practice had long favoured compressed air brake systems, the leading pattern being a proprietary Westinghouse system. This has a number of advantages, including smaller brake cylinders (because higher air pressure could be used) and a somewhat more responsive braking effort. However, the system requires an air pump. On steam engines this was usually a reciprocating steam-driven compressor, which was quite bulky and much more complicated and maintenance-intensive than the vacuum ejector, which was compact and had no moving parts. The compressor's distinctive shape and the characteristic puffing sound when the brake is released (as the train pipe has to be recharged with air) make steam locomotives fitted with the Westinghouse brake unmistakable. Another disadvantage of the earlier air brake systems (although later overcome) was that it was impossible to make a partial release. The vacuum brake can very simply be partially released by restoring some (but not all) of the vacuum, without having to fully release the brakes. The original air brake systems, on the other hand, did not allow this, the only way of partially releasing the brake being to fully release it, then re-apply it to the desired setting.