Valve closure system and valve closure assembly

An assembly for turning an external handle of a tank dome valve about a vertical axis, the assembly comprising:

• a mounting for removably mounting the assembly on a tank dome,
• an adapter operated by a motor for engaging the valve handle and turning the handle when the motor operates, and
• a positioning mechanism for selectively positioning the adapter relative to the mounting to establish a spatial relationship of each to the other for enabling the mounting to be placed at a desired location on the dome and the adapter to engage the valve handle, wherein the positioning mechanism comprises two degrees of freedom of motion in a horizontal plane for establishing the spatial relationship of the adapter to the mounting in the horizontal plane,
• in which the mounting comprises a clamping mechanism for fitting and clamping onto a rim of an upright wall of the dome bounding a zone of the dome containing the valve,
• in which the positioning mechanism comprises a first part supported on the clamping mechanism and a second part that comprises an association with the first part for providing the positioning mechanism with a first of the two degrees of freedom of motion that extends along a circular arc centered on the first part,
• in which the first part comprises an upright post on the clamping mechanism and the association of the second part with the first part comprises a joint that allows the second part to turn on the post about a vertical axis of the post for causing the first degree of freedom of motion to extend along a horizontal circular arc centered on the vertical axis, and in which the joint comprises a linear bearing between the post and the second part to allow the second part not only to turn on the post about the vertical axis of the post but also to be positioned vertically along the post.