Section 9. Pursuant to the provisions of this section, an appointing authority may make a promotional appointment within a departmental unit on the basis of a departmental promotional examination. Such departmental promotional examination shall be open, until there are at least two employees in lower titles eligible to apply, only to persons who have been employed in the departmental unit as civil service employees for at least one year immediately preceding the date of the examination, who have no permanent status in such unit in a title higher than the examination title, and who have been employed in such unit as civil service employees in a title equal to that of the position for which the examination is to be held or in the next lower titles, as determined by the administrator, for at least one year at any time preceding the date of the examination.