The development of butterfly valve
2008-07-30

        A 200-inch butterfly valve was successfully manufactured by German companies ROPO. It is not only the largest butterfly valve in Germany, maybe also the largest butterfly valve in the world.        

         In fact as early as the 1930s, the first butterfly valve had been invented. But until the 1950s, the predominant valve types used in industrial service were long-stroke linear gate valves for on/off applications and globe valves for control. To counteract the problems inherent with linear valve designs, which included relative large size and weight, high operating force and tendency to leak, the rotary ball and butterfly valve designs were introduced. The 1960s marked the introduction of the high-performance butterfly valve.         Instead of a long stroke, the rotary valve requires just a quarter turn (90º) to cycle from the full open to full closed position. The compact design results in a smaller and lighter valve. The short travel distance and reduced surface friction means that the rotary valve can operate with a much smaller and less expensive actuator, and the complete valve package can be significantly smaller and lighter for ease of installation. Reduced moving surface contact area within the rotary valve body has made it possible to develop high-performance sealing technology that can eliminate internal leakage. 

                                                 A butterfly valve is a type of flow control device, typically used to regulate a fluid flowing through a section of pipe. The valve is similar in operation to a ball valve. A flat circular plate is positioned in the center of the pipe. The plate has a rod through it connected to an actuator on the outside of the valve. Rotating the actuator turns the plate either parallel or perpendicular to the flow. Unlike a ball valve, the plate is always present within the flow, therefore a pressure drop is always induced in the flow regardless of valve position.          A butterfly valve is from a family of valves called quarter-turn valves. The "butterfly" is a metal disc mounted on a rod. When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the process fluid. The valve may also be opened incrementally to regulate flow.          There are different kinds of butterfly valves, each adapted for different pressures and different usage. The resilient butterfly valve, which uses the flexibility of rubber, has the lowest pressure rating. The high performance butterfly valve, used in slightly higher-pressure systems, features a slight offset in the way the disc is positioned, which increases the valve's sealing ability and decreases its tendency to wear. The valve best suited for high-pressure systems is the tricentric butterfly valve, which makes use of a metal seat, and is therefore able to withstand a greater amount of pressure.          The concept of a high-performance butterfly valve was first advanced by the US space program in the 1950s. There was a need for a compact, lightweight, tight shut-off valve for the Atlas rocket fuel system. The valve used for this purpose was a single seat, unidirectional shut-off valve with a single offset disc that operated against a polymeric seat. Since the space race launched the high-performance butterfly valve, there have been many design enhancements that improve butterfly valve's performance and range of applicability.          Today, butterfly valves have proven their endurance and dependability in a wide range of industries and applications. They are available in line sizes from 2 1/2" to over 72", temperature ratings from cryogenic to 1500º F, and pressures to 1440 psi. Butterfly valves are used in isolation and control services, and with media such as slurries, steam, gases and liquids. Some of the notable applications include pulp stock, corn processing slurries, tertiary petroleum recovery, high pressure water, high cycle air separation services (both at ambient and cryogenic temperatures), LNG and commercial HVAC to name only a few.           Butterfly valves are the fastest growing segment of the total valve market today because of their numerous advantages, which include: Tight Shutoff. Offset shaft and eccentric disc arrangements combined with modern single piece, flexible-lip, polymeric seats provide bubble-tight shutoff over a wide range of operating conditions. Lightweight/Compact. Because the butterfly valve has a significantly narrower face-to-face dimension and a shorter centerline to the top of the valve profile, it uses less metal than a gate valve. The result is significant weight and size reduction for the same or higher rating. These factors also have a positive impact on piping and plant design. Extended Cycle Life. The double eccentric disc and shaft, in combination with polymeric seats, reduces seat wear and dramatically increases leak-free life cycles. Ease of Maintenance. Compared to many valve types, butterfly valves are easy to maintain. In one design, the insert can be removed with a screw driver and the self-aligning seat replaced. All this can be done on site and the valve can be put back into the line immediately. No machining is required as with gate valves. Ease of Automation. Butterfly valves are easily automated. Every valve is drilled and tapped to accept linkage for a broad range of actuators. Unlike the gate valve, there is no need to purchase a special yoke or other device to modify the gate valve body to accept actuation. And because butterfly valves are quarter-turn, the actuated valve profile is much smaller than linear valves. Wide Temperature Range. High-performance, flexible-lip seals extend the operating temperature range of butterfly valves. Lower Costs. Butterfly valves are less expensive than most other valve types. With actuation, the total cost ratio of the valve package is reduced even further, especially in larger sizes. Ease of maintenance, actuation and installation can also dramatically reduce total life cycle costs. Disadvantages The primary drawback of a butterfly valve is that the disc and shaft are situated in the waterway. Therefore, butterfly valves are inappropriate designs when full flow is required, or when a device (i.e., a pig) will be periodically used to clean the lines.         With few exceptions, high-performance butterfly valves provide tight shutoff, a long life cycle, and life cycle costs that are lower than any other alternative. Large numbers of butterfly valves are being used today to replace both globe and gate valves, which were first specified decades before the development of the high-performance butterfly valve. Butterfly valves also may be a more cost-effective replacement for ball valves. The total presence of butterfly valves will continue to grow in comparison to other valve types as they make their way into more industrial shut-off and control applications.