The present invention features installation system (10) for facilitating the installation and removal of a closure onto and from pressure vessel (22), respectively. Installation system (10) comprisesfixed support structure (40) constructed proximate pressure vessel (22); valve carriage (60) dynamically and continuously supported by fixed support structure (40), wherein valve carriage (60) also dynamically and adjustably supports a closure, such as a header or deheader valve (14), in a continuous manner; elevation adjustment assembly (90) allowing valve carriage (60) and the closure to move ina vertical manner relative to fixed support structure (40) and pressure vessel (22); and horizontal transfer assembly (110) that dynamically couples the closure to valve carriage (60) to enable horizontal, bi-directional transitioning of the closure relative to valve carriage (60). Elevation adjustment assembly (90) and horizontal transfer assembly (110) work in harmony together to provide both approximate and precision vector positioning of the closure to enable parallel and concentric alignment with pressure vessel (22). In this manner, the closure may be installed and removed from pressurevessel (22) in a much safer and more efficient manner.