Hi Liecdre. Welcome to the board.
It sounds like you're trying to protect a pressure vessel, in which case you will need a valve that conforms to the laws in your country. In the US for example, ASME code vessels must have ASME code pressure relief valves on them to protect them. If in the US, I'd start with the Anderson Greenwood pilot operated valves shown on page 7 of this brochure. Contact your local representative for details. http://valves.pentair.com/valves/Images/PVCMC-0334-US_tcm106-13900.pdf
You will of course have to determine the capacity of the valve by performing an analysis on the process. If the potential for over pressure is from heating or boiling for example, the analysis has to examine how the heat can potentially over pressure the vessel/system. A fire case might also need to be examined. I'd suggest locating someone to help you at your place of employment to assist you in determining what the requirements are for the various cases the valve has to be capable of handling.