What is a rubber lined / concentric butterfly valve?

What is a rubber lined / concentric butterfly valve?

Concentric butterfly valves also known as ‘resilient seated’ butterfly valves are suitable for a wide range of applications such as cooling water, chemicals, brine,oil mud, hydrocarbons, wastewater, firewater, seawater, natural gas and flare gas amongst many others. The stem is centred in the middle of the disc and the disc centred in the valve body. The disc is constantly in contact with valve seat. Seats can include EPDM, NBR, Viton, Silicon, Teflon, Hypalon and neoprene.