Butterfly Valves — API 609 Category A & B

What is a Butterfly Valve?

A butterfly valve has a disc mounted on a shaft in the centre of the flow path. A quarter turn moves it from closed to fully open. The valve is short and light compared with gate or ball valves of the same size, which makes it economical in large lines. Concentric, rubber-lined valves suit water and low-pressure service. Double offset (high-performance) and triple offset designs move the disc clear of the seat as it opens, allowing metal or PTFE seats, higher classes and tight shutoff in hydrocarbon and steam service.

Key features

• API 609 Category A: concentric, resilient-seated, CWP rated
• API 609 Category B: double offset and triple offset, ASME class rated
• Wafer, lug, double-flanged (short/long pattern) and butt-weld bodies
• Resilient, PTFE/RPTFE or laminated metal seats
• Lever, gear or actuator; fire-safe design to API 607 on request

Specification

Applications

• Cooling water and seawater intake
• Firewater and utility water
• HVAC and district cooling
• Hydrocarbon and steam isolation (triple offset)
• Large-diameter process lines

Concentric vs triple offset butterfly valve

A concentric valve has the shaft through the disc centre and seals on a rubber liner; it is economical for water and low-pressure service but limited by elastomer temperature. A triple offset valve offsets the shaft twice and the seat cone once, so the disc lifts clear without rubbing and seals metal-to-metal. It handles higher temperatures and classes and gives tight shutoff in hydrocarbon and steam lines.