Butterfly valves are not only widely used in petroleum, gas, chemical and water treatment, but also in the circulating water system of power plants.Wafer and flange are two types of connecting.Flange butterfly valve body has flange on both ends, connected to pipe flange.
There are no flanges on both ends of the butterfly valve body, only guide bolt holes, and the valve is connected to the flange of the pipe end with a set of bolts/nuts.
 
It's cheap and light for wafer butterfly valve.
The bolt length of wafer butterfly valve is longer, and the installation precision is higher than flange butterfly. If the flange of pipe is not correct on both sides, the bolt will be subjected to greater shear load, and the valve will leak easily.
In contrast, the disassembly of the wafer butterfly valve is convenient, the valve cost is low, but the disadvantage is that one sealing surface problem, two sealing surface must be opened.
The sealing of Flange butterfly valve is relatively more reliable, but the valve cost is relatively higher.And the wafer butterfly valve usually cannot be used in the end of the line , because when the end flange is removed, the wafer valves will drop down,  In this case, the valve must be installed pipe joint on the other end before it can be removed, and flange butterfly valve is not the above problems, but the cost will be high.Generally, the valve bolts are longer for wafer butterfly valve. Under high temperature conditions, The valve could be caused external sealing leakage after expansion of bolts, so it is not suitable for large pipe diameter under high temperature conditions.