What is API 609 Standard?

API 609 is the American design standard for butterfly valves, which is divided into Category A and B.

What is an API 609 Butterfly Valve?

A butterfly valve is used to shut off or modulate the flow of a fluid (isolation and regulation). API 609 Centric butterfly valves (soft seated) are preferred to gate and ball valves for low-pressure and non-critical applications as they are cheaper, lighter, and easier to install. Eccentric butterfly valves (double offset and triple offset valves) with metal seats have surged in popularity and compete with globe and ball valves for some applications.

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Types of API 609 Butterfly Valve

API 609 Category A Butterfly Valve

The Centric or concentric butterfly valve is the primary type of butterfly valve design. In this design of the valve, the stem crosses from the centerline of the disc. Between the pipe bore and the seat, there is the inside diameter boundary. This zero-offset valve is also called resilient-seated because it relies on the adaptability of the seat rubber to seal the flow after closing it efficiently. At around 85° during a 90° rotation, the disc first comes into connection with the seat in this kind of valve. Concentric butterfly valves are generally used for low-pressure applications.

API 609 Category B Butterfly Valve

In the eccentric butterfly valve, the stem passes behind the centerline of the disc instead of passing through it. As the stem is positioned behind the centerline, the valve is called a single offset. This design helps to minimize the disc contact with the seal, which increases the service life of the valve. In double-offset butterfly valves or doubly eccentric butterfly valves, the stem is positioned at the backside of the disc with an extra offset. This stem design allows the rotating disc to cover the seat only for one to three degrees. A triple offset butterfly valve is frequently used in more complex applications that have the same design as a double offset butterfly valve. A triple offset butterfly valve is efficient and reduces wear. This valve has metal seats that create a bubble-tight shut-off and make it able to use in higher temperature applications.