Case Entity how to use with Approval level?

Hi All,

 I am using case entity for service request processing in my solution. The case will be created by different departments users inside the CRM.

For some cases i need to get approval from the Department managers before it goes to the Request Manager. 

The request manager only assigns the request to Technicians for resolving.

Any one can suggest how to do it? or any exaple for executing this process flow.