It is critical (pun intended) that you have a criticality ranking for your equipment. This will help you properly direct maintenance and reliability efforts. It is difficult to have granularity on the actual role equipment plays if the criticality scale is small (1-10). It is best to use a higher scale with categories that comprise the overall ranking. For example use a 100-scale with 10 categories and each one being 0-10.
Watch our Reliability Matters video tutorials