Connecting type of generally API butterfly valve include flange type, wafer type, lugged type . Due to limitation of construct, some of body-flange hole need to be drilled and tapped , some need to be through hole.
Taking the API butterfly valve 150LB as an example, for the flange type valve, the NPS 20 or larger valve, four holes in position of upper and lower stem is required to be drilled and tapped; for wafer type valve, valve size NPS16 and larger, the four holes in same position is requested to be drilled and tapped; for lug-type butterfly valve, all body-flange holes need to be drilled and tapped.
How to choose the srcew of body-flange hole ？
According to API609 standard, threaded body-flange holes for 1inch or less in diameter shall be drilled and tapped in accordance with ASME B1.1, coarse-threaded series, class 2B, for bolts 1 1/8inch or more in diameter, such holes shall be drilled and tapped in accordance with ASME B1.1, eight-thread series, class 2B.
For the threaded bolt boles shall allow full threaded engage-ment to a depth at least equal to the nominal bolt diameter, however, ehen the bolt hole is adjacent to the shaft, engage-ment to depth of 67% of the nominal bolt diameter is acceptable .
Zhejiang Zhengfeng Valve .