Self-limiting device of valve

The utility model provides a self-limiting device of a valve. The self-limiting device of the valve is composed of a valve body, a ball body, a valve rod, limiting keys, a lengthened rod, a valve cover and a lengthened support, wherein the ball body is arranged in the valve body, the valve rod is arranged at the upper end of the ball body, the lengthened rod is connected with the top end of the valve rod, the lengthened support is connected with the top end of the lengthened rod, the valve cover is spherical and arranged outside the valve rod, the limiting keys are arranged at two ends outside the valve rod and upper portion of the valve cover and fixed in limiting key grooves at two ends outside the valve rod, and the valve cover is in a limiting arc shape. When the valve cover rotates at an open angle from 0 degree to 90 degrees, namely the valve seat of the valve is fully opened, the limiting keys are matched with the limiting arc shape in a clamped mode to achieve a limiting function. When the valve cover