Thermoplastic Butterfly Valves are available in two types/styles: wafer or lug. A different installation procedure is used for each one.
Wafer Style Butterfly Valves Wafer style is the more common of the two and is less expensive than the lug style. The wafer style butterfly valve is just about the standard. It ís so common that no one even bothers to use the word "wafer" when ordering a butterfly valve. It is taken for granted that if a butterfly valve is ordered, a wafer style will be received.
Installation of the Wafer Style Butterfly Valve Butterfly valves are installed by inserting the valve between two flanges using bolts or studs and nuts to hold it all together. This type of installation, of course, makes it impossible to disconnect just one side of the piping system from the valve. That benefit is received using the lug style valve.
Installation of the Lug Style Butterfly Valve Lug style valves have threaded metal inserts (usually stainless steel) installed in the valve's bolt holes. The inserts are threaded on both ends. This allows the lug style valve to be installed into a system using two sets of bolts and NO nuts for each hole. The valve is installed between two flanges using a separate set of bolts for each side of the flange. This setup permits either side of the piping system to be disconnected without disturbing the other side.
Lug Style Butterfly Valves Lug style butterfly valves used in dead end service generally have a reduced pressure rating. For example most sizes of Hayward butterfly valves mounted between two flanges have a 150 PSI pressure rating. The same valve mounted with one flange, in dead end service, has a 75 PSI rating.