I have a chat system in my site.
When i press ctrl+f5 buttons the chat will be refeshed with online and offline members and it will logout the page and display the login page.
Can I clear session values by pressing ctrl+f5 buttons?
What you're referring to is a hard-refresh, which clears your cache and forces resources to be downloaded again. Doing a hard refresh doesn't destroy session variables. Destroying a session destroys session variables.