gas holder in 1890. Instead of external columns or guide frames, his design operated with spiral rails. The first commercial design was built in Northwich, Cheshire, in the same year. By the end of the 19th century most towns in Britain had their own gas works and gas holders. The years between the two world wars were marked by improvements in storage, especially the waterless gas holder, and in distribution, with the advent of steel pipes to convey gas at up to as feeder mains to the traditional cast-iron pipes. Municipal gas works became superfluous in the later 20th century, but gas holders and production plant were still in use in steel works in 2016. Function A gas holder provided storage for purified, metered gas. It acted as a buffer, removing the need for continuous gas production. The weight of the gas holder lift (cap) controlled the pressure of the gas in the mains and provided back pressure for the gas-making plant. They are the only storage method that keeps gas at district pressure (the pressure required in local gas mains). Types There are two basic types of gas holder: the water-sealed and the rigid waterless. The water-sealed gas holder consists of a tank of water that rises and falls to take the gas. A watered gas holder consisted of two parts: a deep tank of water used to provide a seal, and a closed vessel (the lift) that rises above the water as the gas volume increased. Rigid waterless gas holders were a very early design that neither expanded or contracted. There are modern versions of the waterless gas holder, e.g. oil-sealed, grease-sealed and "dry seal" (membrane) types. They consist of a fixed cylinder capped by a moving piston. Water-sealed gas holders The earliest Boulton and Watt gas holders had a single lift. The tank was above ground and was lined with wood; the lift was guided by tripods and cables. Pulleys and weights were supplied to regulate the gas pressure. Brick tanks were introduced in 1818, when a gas holder would have a capacity of . The engineer John Malam devised a tank with a central rod-and-tube guide system. Telescoping holders fall into two subcategories. The earlier of the telescoping variety were column-guided variations and were built from 1824. To guide the telescoping walls, or "lifts", they have an external fixed frame, visible at a fixed height at