Industrial valves and fittings. A valve is a mechanical or natural device that controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing numerous channels. Industrial valves are designed to withstand tremendous pressure, whether from fluid or gas, and to last for years in difficult situations. Valves are mechanical devices that regulate the flow and pressure of a system or process. They are critical components of a piping system that transports liquids, gases, vapors, slurries, and other substances.