Dear CSAaras.ali,
Control.com has a very powerful 'Search' feature located at the top of every Control.com webpage. Just click on the magnifying glass icon.
Using the search term "secondary" (without the double quotes) yielded this result (not at the top of the results; sometimes the most relevant search results aren't always in the tip three or five results...!):
Fuel purge | Automation & Control Engineering Forum
Hope this helps!