Hattersley automatic air vents (Fig. 775/776) are brass-bodied, WRAS-approved devices designed for closed-circuit heating and cooling systems to automatically remove trapped air, preventing corrosion, pump cavitation, and circulation issues. They operate up to 10 bar, with temperature limits of 110–120 °C, and include polypropylene floats with EPDM seals. Available in ⅜″–1″ BSP sizes, some models incorporate hygroscopic safety caps to limit leakage, while the Fig. 776 includes a shut-off valve option for easy removal without draining the system. Installed vertically, they ensure efficient system performance and reliability.