The new Conbraco spill-resistant vacuum breaker (SVB) prevents cross-connections without allowing a water spill. Designated the 4W-500 Series, the new valve is designed to prevent contamination of the potable water supply due to back-siphonage. The SVB is suited for continuous pressure, indoor applications where water spillage is undesirable. During normal flow conditions, the SVB's check valve remains open and the atmospheric vent seals in the bonnet assembly. As the line pressure falls to 1 psi, the spring loaded atmospheric vent opens and the check valve closes, breaking the vacuum and preventing the back-siphonage. Available in 1/4", 3/8" and 1/2" sizes.Conbraco Industries.