The indicator valve, code P50508-07, is a crucial diagnostic component mounted on the MAN L21/31 cylinder head, enabling engineers to measure internal cylinder pressure during engine operation. By allowing temporary access to the combustion chamber, it facilitates performance analysis through indicator diagrams and helps detect abnormalities such as misfiring, loss of compression, or injector malfunction. Its robust construction ensures safe operation under high-pressure conditions, making it an indispensable tool for preventive maintenance and engine tuning in marine and industrial applications.