Renival of CPCB Approvals for Generators

Dear Team , is it mandatory for renival of CPCB (Central Polution COntrol Board) once the Manufacture is issued CPCB Cirtificaion ,  or do we have to go once again after specific run hour of Equipment of Diesel Generator for re verificlain , Do we need revival of CPCB certificate in case Equipment is Older and in use for specifice years

Please Clear the Matter

thanks

Shivakumar