Honeywell DU145 Automatic By-Pass Valve 22mm - Angled The Honeywell DU145 Automatic Bypass Valve controls flow of water through a bypass circuit which is installed between flow and return pipework, typically at or near the boiler. Building Regulation advice states that if a bypass is installed, an Automatic Bypass Valve must be fitted. Key Features and Benefits: Angled 22mm Automatic By-Pass Value Unique and Simple Adjustment Mechanism Wide Differential Pressure Range 0.1 to 0.6 Bar 22mm Compression Fittings for Ease of Installation Ensures Constant Flow Through Boiler Reduces System Noise and Maintains an Even System Pressure Height: 48mm Width: 72mm Depth: 118mm Manufacturers 1 Year Guarantee