Butterfly valve's clamp and flange are two connection methods. In terms of price, the wafer type is relatively cheaper, the price is roughly 2/3 of the flange. If you want to choose imported valves, try to use the wafer type as they are cheap and light in weight.
The bolts of wafer-type valves are longer and require higher construction accuracy. If the flanges on both sides are misaligned, the bolts will be subject to greater shear force and the valve will easily leak.
Wafer-type valve bolts are generally relatively long. Under high-temperature conditions, the expansion of the bolts may cause leakage, so they are not suitable for large-diameter pipes under high-temperature conditions. Moreover, the wafer-type butterfly valve generally cannot be used at the end of the pipeline and in situations where disassembly is required downstream, because when the downstream flange is disassembled, the wafer-type butterfly valve will fall off. In this case, a separate nipple must be made. To facilitate disassembly, the flange butterfly valve does not have the above problems, but the cost will be higher.
There are no flanges at both ends of the wafer butterfly valve body, only a few guide bolt holes. The valve is connected to the flanges at both ends with a set of bolts/nuts. In comparison, disassembly is easier and the valve cost is lower. However, the disadvantage is that if there is a problem with one sealing surface, both sealing surfaces must be disassembled.
The flange butterfly valve body has flanges at both ends and is connected to the pipe flange. The sealing is relatively more reliable, but the valve cost is relatively high.