The Schneider Electric (Erie) VT2323G23A020 is a 24V usually open zone valve used to control fluid flow in HVAC systems. This 3/4-inch valve has a two-position spring-return mechanism. In its usual state, the valve is open, enabling fluid to flow. When activated with a 24V AC signal, the valve closes, halting the flow. https://www.partshnc.com/vt2323g23a020-schneider-electric-erie-24v-no-34-npt-2w-valve