Venturi Funnel creates smoother air outlet flow and gives sharp and appearing sound. Recirculation flange also available as an optional at choice of Dia. 22mm / 28mm / 34mm. Dual drive has two individual ports allows to adjust releasing volume of air to match a requirement. Piston controls amount of air release accord by pressure. Body - Lightweight aluminum alloy die cast body with radiation fins provides ultimate hemolytic action. Valve - Dia. 36mm big valve made by lightweight aluminum alloy. Super Sound Blow Off Valve VD can be use for either open atmosphere or recirculated. Recirculation flange sold separately as optional to convert open atmosphere to recirculated. Flange diameter available at choice of 22mm / 28mm / 34mm.