 At this time some trains were still worked by locomotives, but from 23 February 1848 all scheduled trains were powered by the atmospheric system.The leather valve along the top of the pipe tended to dry out and air could then leak in, but this was mitigated slightly by the passing trains spraying water on the leather.The harsh environment of the line, which runs adjacent to the sea for much of its length and is often soaked with salt spray, presented difficulties in maintaining the leather flaps provided to seal the vacuum pipes, which had to be kept supple by being greased with tallow; even so, air leaked in, reducing the pressure difference.