US Patent 7174911 Fire hydrant with second valve

Fire hydrants which feature additional structure for reducing the potential that those with ill intent can foul municipal water supplies by introducing toxins or other materials into fire hydrants. Various embodiments include valves which close off portions of the hydrant otherwise available for receipt of toxic or other materials when the fire hydrant nozzle cap is unscrewed and open. Such valves preferably open, manually or automatically, when water is flowing from the water supply through the nozzle, a condition which renders it difficult at best to introduce toxins through the hydrant into a water supply, but close off portions of the barrel when the nozzle is open and water is not flowing through the nozzle.