Dual-butterfly non-return valves
The word ’butterfly’ in the name of dual-butterfly non-return valves describes the structure of the valve rather well. In the middle, there is a closing axle, and there are hemisphere-shaped closing flaps symmetrically on both sides of the axle.
Unlike its competitors, GESTRA uses two separate axles, and each closing flap is secured with two separate closing springs (in conventional solutions, there are usually no closing springs). The robust structure aims at to protecting the valve against damages caused by minor water hammer. In the case of extensive water hammer in the system, the BB dual-butterfly non-return valves can be fitted with special hydraulic dampers.
Non-existing flow resistance
An unquestionable advantage of dual-butterfly non-return valves is their low flow resistance (at only a few mbar, depending on the flow rate). In other models, it can be a hundred times higher. The flow resistance of a valve can additionally be adjusted through the choice of springs. The flow resistance depends on the valve installation position and springs used. For example, in a vertical pipe with an upward flow, the force required for valve opening is larger as compared to a horizontal pipe, for example. If required, our vendors will provide you with more specific information on the opening of each valve and offer assistance in dimensioning.
BB dual-butterfly non-return valves are available in different materials, as well as coated for seawater use.