Backflow prevention devices are designed to protect the public water supply from cross-connections. A modern community water supply system is designed to ensure that water flows to properties and buildings under pressure. This community water network contains many users where there is a risk to public health if there is a cross-connection between the water supply and a contaminated source. A cross-connection can occur where there is a pressure drop in the water main. This pressure drop causes a vacuum and siphons of entrainment water from end-users into the public water supply.