The sealing ring is deformed. Generally speaking, the design thickness of the sealing ring is just tight when tightening the cup. But if the sealing ring expands, or the sealing ring falls out, it is installed backwards. It will lead to the situation that the sealing ring is pressed but the cup cover is not pressed. At this time, because the cup can still be tightened, the rubber ring will slide with the cup mouth. So ... . . Take out the sealing ring and replace it, install it carefully and try again. Of course, remember to drain the water in the water tank with a paper towel before installing the leather pad.