Shut-off valves are used to regulate the flow of liquids or air. Drain cocks allow water to drain down whereas air cocks control the flow of air into a plumbing system or gas line. The water supply to a faucet, toilet, or an appliance such as a washing machine is turned off. The mixing of water, chemicals, and inert gases is controlled by water valve kits. Clean water is protected by check valves, which prevent backflow. Water, oil, and natural gas systems can all benefit from ball valve assemblies.