control member 3 includes a circular plate with a center thereof perforated with an axial perforation 33 similar to the axial perforations 201 and 211 the axial pole 16 penetrates through the second control member 3 at the axial perforation 33 in this embodiment the contour of the space 10 of the body member 1 is conformal to the periphery of the second control member 3 such that the second control member 3 can freely rotate relative to the first control member 2 within the space 10 the control switch 4 is mounted at the other side of the body member 1 and linked with the second control member 3 by controlling the control switch 4 the relative rotation between the first and second control members 2 and 3 is generated in this embodiment the control switch includes a control handle 40 a lid 41 covering the other side of the body member 1 and a shaft 42 connecting the lid 41 and the control handle 40 to the second control member 3 by moving the control handle 40 the second control member 3 is rotated relative to the first control member to ensure the body member 1 and the lid 41 being closely engaged to avoid water leaking into the body member 1 a sealing ring 410 is installed between the lid 41 and the body and a sealing ring 420 can be installed between the shaft 42 and the lid 41 while moving the control hand 41 of the control switch 4 a positioning effect is also obtained by forming a positioning recess 34 on the second control member 3 a positioning column 411 extending from the lid 41 and an elastic positioning bead 43 in the positioning.