Dual-plate check valves prevent return flow in horizontal and vertical pipelines. They are wafer-type valves of double swing design. For installation in horizontal pipelines, they are fitted with closing springs. For installation in vertical pipes with upward flow, closing springs may be included if required. For installation in vertical pipes with downward flow, they require 5VO closing springs. Dual-plate check valves can be used for liquids, gases and vapours in accordance with the Pressure Equipment Directive.