A valve is a device that controls the flow of a fluid or gas. A valve is a product rarely noticed by the average person, yet it plays an important role. Each time you turn on a faucet, use your dishwasher, turn on a gas stove, or step on the accelerator of your car, you operate a valve. Without modern valve systems, there would be no fresh pure water or automatic heat in your home. One of the mostly widely observed but least recognized type of valve is the fire hydrant. They are specialized underground valves that can be opened and closed from ground level when needed in emergency situations. Today’s valves can control not only the flow, but the rate, the volume, the pressure or the direction of liquids, gases, slurries or dry materials through a pipeline or similar passageway. They can turn on and turn off, regulate, modulate or isolate. They can range in size from a fraction of an inch to as large as 30 feet in diameter and can vary in complexity from a simple brass valve to a precision-designed control valve made of an exotic metal alloy. Valves can control flow of all types, from the thinnest gas to highly corrosive chemicals, steam, abrasive slurries, toxic gases and radioactive materials. They can handle temperatures from cryogenic to molten metal, and pressures from high vacuum to thousands of pounds per square inch.