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Normally butterfly valves are used as on-off valves and are usually installed in a valve chamber on the water side of bottom outlet lines in dams or in gravity lines leading to water treatment plants or hydro-power plants. In the best case the butterfly valves are assembled with brake and lift cylinders, working as pipe brake devices for emergency quick closing by lever and weight in case of pipe bursts. In dam applications, control valves such as plunger valves (or needle valves) or hollow-jet valves (or Howell Bunger valves or Fixed Cone valves) are installed after the butterfly valves on the air side. These valves always work as flow regulating or control valves. Plunger valves or hollow-jet valves are designed to perform regulating or control functions in water supply systems. Unlike butterfly valves or gate valves assuming only shut-off functions in pipeline systems, plunger valves and hollow-jet valves can meet the requirements of regulating operations.