In double offset butterfly valves, the stem axis is offset behind the centreline of the seat and the body (first offset), then the stem axis is further offset from the vertical centreline of the valve (second offset). When the disc is opened, the seat is lifted from the seal; this reduces the friction during the first and last 10 degrees of the valve opening and closing, respectively. This results in a smoother valve operation, better sealing capability, and longer service life than the zero offset butterfly valve.
Similar to zero offset butterfly valves, double offset butterfly valves also utilize a soft seat. However, they are designed to handle moderate pressure and temperature conditions better than their zero offset counterparts, making them suitable for higher pressures and temperatures in liquid and gas pipelines.
Double offset butterfly valves are commonly employed in applications such as water purification, wastewater treatment, HVAC systems, and fire protection systems like fire sprinklers. To enhance temperature resistance, these valves often feature a metal backing that reduces the amount of soft seat material