Double eccentric design of valve plate and valve stem The double eccentric design reduces the wear of the valve seat and ensures the two-way air-tight closing function in the entire pressure range. At the starting point of the valve seat, the eccentric valve plate has a cam-like effect, and the valve plate can be pulled away from the valve seat without excessive pressure. The function of the valve plate in the starting position is similar to the cam member, which reduces the wear of the valve seat and minimizes the deformation of the valve seat. When the valve is opened, since the valve plate does not touch the valve seat, the life of the valve seat is prolonged and the operating torque is small. When the valve is closed, the rotary motion of the valve similar to the cam action is a linear motion, which effectively pushes the valve plate to the valve seat. The action of the valve plate on the valve seat prevents the accumulation of foreign matter such as mud and suspended solids.