Lug-style butterfly valve
Lug-style valves have threaded holes on both sides of the valve body. This allows them to be installed using two sets of bolts without nuts. The valve is installed between two flanges using a separate set of bolts for each flange. This method has the advantage of having either side of the piping system be removed without affecting the other side during maintenance or replacements.
A lug-style butterfly valve used in dead end service generally has a reduced pressure rating. For example, a lug-style butterfly valve mounted between two flanges has a 1,000 kPa (150 psi) pressure rating. The same valve mounted with one flange, in dead end service, has a 520 kPa (75 psi) rating. Lugged valves are very resistant to chemicals and solvents, they can also handle temperatures up to 200 °C, which makes it a versatile solution.
Lug styled butterfly valves function in much the same way as wafer butterfly valves which you can read about here. In that article we discuss that butterfly valves come in many different forms and sizes made to address the various situations where they may be needed as a solution.