The double offset butterfly valve is a further improvement on the single offset butterfly valve. Its structural characteristic is that the valve stem axis deviates from both the center of the disc and the center of the body. The effect of the double offsetity is that the disc can quickly leave the seat after the valve is opened, greatly reducing the excessive compression and friction between the disc and the seat, reducing the opening resistance and wear, and increasing the seat life. With significantly reduced friction, the double offset butterfly valve can also use a metal seat, improving the application of high-performance butterfly valves in high-temperature areas.
Replacing the seal is more convenient. To replace the seal of the double offset butterfly valve, you only need to remove the four screws, take down the disc, install the gasket inside, and tighten the four screws. The process is relatively complex for the triple offset butterfly valve. The high-performance butterfly valve adopts a double offset structure, which has better sealing performance than the centerline butterfly valve.
A lighter torque means a longer life for pneumatic or electric actuators. Generally, the centerline butterfly valve only lasts 30,000 to 50,000 cycles, with the maximum diameter being around 80,000 cycles. At the same diameter, the high-performance butterfly valve can last up to 1 million cycles. The high-performance butterfly valve is suitable for high-frequency switching.
The sealing structure of the high-performance butterfly valve is different from that of the centerline butterfly valve. The centerline butterfly valve is lined with rubber, while the high-performance butterfly valve's sealing is inside, pressed by a plate. The sealing contact surface is smaller. The disc of the high-performance butterfly valve is thicker than that of the centerline butterfly valve, and when the thickness of the disc and the thickness of the contact surface are proportional, the sealing performance is also very good.
The fire-resistant structure of the valve is useful for firefighting. If a pipeline catches fire and a centerline butterfly valve is used, it may melt. The sealing material of the high-performance butterfly valve is PTFE, which can withstand temperatures of up to 200°C, and the sealing is inside. Even if the temperature is too high, the sealing is not easily burnt. Even if the centerline butterfly valve's sealing is also PTFE, it will still melt because the sealing is on the outside with a larger contact surface.
When the disc of the double offset butterfly valve is pressed, it just covers the entire sealing interface. When there is a fire, the inside is not affected because the pressure plate covers the sealing interface. The sealing surface is not easily damaged, and for a short period, it can resist high temperatures. Generally, the sealing surface of the high-temperature structures can last for about an hour. However, this is not the case for the centerline butterfly valve. Generally, it would deform after an hour of high temperature, and when the sealing deforms, the valve cannot be used anymore.