Nov.07.2024
Butterfly valves come in two main types: flanged butterfly valves and wafer butterfly valves. Flanged butterfly valves come with their own flanges, eliminating the need for additional consideration. However, for wafer butterfly valves, flanges must be separately chosen and fitted after purchase for installation onto the pipeline. So, what kind of flanges should be selected if one chooses not to use the manufacturer's supplied flanges and instead opts to choose flanges according to standard specifications?
In general, pipeline pressure ratings for wafer butterfly valves are not very high, so flanges should be selected based on the pressure rating of the pipeline. Flange pressure ratings should match the pressure ratings of the butterfly valves. To avoid installation complications, it's best to specify bolt-hole spacing, which also facilitates supply from manufacturers. It's advisable to leave some extra room, adding the thickness of the butterfly valve plus the thickness of two flanges and the nut thickness. Additionally, pay attention to the bolt-hole diameter of the butterfly valve!
There are many types of flanges available, such as flat welding, neck welding, and socket welding flanges. How should one choose? Typically, one should choose flanges according to the corresponding pressure rating of the pipeline, which will be listed in a pressure rating table. As for flat welding, socket welding, neck, or non-neck flanges, if there are no specific requirements, use two flat face flanges for clamping and secure them with longer bolts.
Wafer butterfly valves must use dedicated flanges, which can be easily matched to the given valve size. The selected flanges must be compatible with the purchased butterfly valves, including the flange sealing surface and standard. This depends on the requirements set during the technical agreement with the valve manufacturer. As for the connection types of flanges: flat welding, socket welding, butt welding, threading, clamp, or flange, it mainly depends on process requirements and design specifications.
Flanges used for wafer butterfly valves are not standard flat welding flanges but are custom-made wafer butterfly valve-specific flanges. This is because wafer butterfly valves have a slightly larger sealing surface diameter. If standard flat welding flanges are used to connect to wafer butterfly valves, the contact area between the flange and the valve will be small, affecting the sealing effect and causing leakage. Therefore, wafer butterfly valve flanges have two different inner diameters, similar in appearance to socket welding flanges without necks, with a smaller inner diameter similar to the valve diameter to ensure sealing effectiveness. Wafer butterfly valve-specific flanges do not have standard numbers; they are made according to industry conventions.
Other dimensions of dedicated flanges for wafer butterfly valves are the same as those of standard flat welding flanges, following flange standards (such as JB81-94, GB9112, ASME B16.5, HG20592, etc.). When the bolts pass through the flanges, they ensure the valve body is not interfered with. Simultaneously, the inner diameter size of the flange should not be too small to ensure that the corresponding valve plate can fully open. The large inner diameter of the flange is the same as that of a standard flat welding flange, 110mm, used for welding with 108mm pipes. For fully lined butterfly valves, choose wafer-style flanges, which are flat welding flanges for socket welding. For metal-sealed wafer butterfly valves, choose flat welding flanges.
In conclusion, the key consideration when selecting flanges for wafer butterfly valves lies in whether the flanges match the valves and meet the requirements of valve processes and designs. The method of connection with the pipeline is secondary.
