Lined butterfly valve and method for manufacturing lined butterfly valve

A lined butterfly valve comprising:

• a body;
• a stem rotatably mounted in the body;
• and
• a valve disk provided rotatably inside the body via the stem, the valve disk including a core metal covered with a lining layer,
• wherein the lining layer comprises a front/back-side lining part provided on each of a front side and a back side of the core metal, and an outer circumferential lining part provided on an outer circumferential side of the core metal,
• wherein the front/back-side lining part has at least a first predetermined lining thickness on each of the front and back sides of the core metal and has, at least at an outer circumferential end position of the core metal, in total on the front and back sides, a thickness obtained by doubling a thickness obtained by adding a thickness equal to a maximum warp width on a valve blade side of the core metal to the first predetermined lining thickness,
• wherein the outer circumferential lining part has a thickness from an outer circumferential end of the core metal to a tip seal surface of an outer circumferential end of the valve disk obtained by adding a second predetermined lining thickness and a predetermined crush thickness,
• wherein each predetermined lining thickness is a minimum thickness required so as to prevent a fluid from permeating through the core metal,
• wherein the maximum warp width is a deviation amount due to a maximum warpage of the core metal that occurs during casting of the core metal or during a lining process, and
• wherein the predetermined crush thickness is an amount of irreversible crush of a convex part on an outer circumference of the valve disk that occurs when the valve disk is opened and closed.