(1) The amount, expressed as a fraction of an inch, by which the valve in mid position overlaps the cylinder steam ports. Valves provided with long lap required greater travel to operate effectively but this allowed a freer exhaust and more sharply defined stages in the cycle of valve events. Long lap valves were introduced on the Great Western Railway in 1908 following importation of the idea from the US but it was not until the 1930s that their value was properly understood by other UK railways. (2) Name given to the position on the driver's brake valve which closes all air ports between the brake pipe and the brake valve itself. Used to hold the brake pipe pressure after a partial application has been made.