A valve is a device that regulates the flow of materials (gases, fluidized solids, slurries, or liquids) by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but usually considered separately. Valves are used in a variety of applications including industrial, military, commercial, residential, and transportation. Oil and gas, power generation, mining, water reticulation, sewerage and chemical manufacturing would constitute the majority of valves used by industry.