In oil system what is the function the bypass valve?

to release oil pressure if the oil filter stuked 

We are using bypass valve when we have work of maintenance in the flow line, (valve of flow line) cleaning or replacing oil filtter during equipment normal running .  

If we want to keep the equipment running and we must repair,replace or maintain the main valve or clean the fillters we use the bypass valve.

We  use bypass valve  when  we have work of maintenance in the flow line (valve of flow line)

Bypass valve is bypassing a clogged filter for example , avoiding the catastrofic fail, or to avoid overpressure over a component

it allows oil to bypass a clogged filter or in case of any malfunction 

During normail operation ,when the filter becoming clogged in the oil system,  the bypass valve opens to allow oil flows directly to the system to assure lubrication of engine moving parts. 

MAINLY BYPASS USE FOR SCHEDULED OR NON SCHEDULE MAINTENANCE REQUIRED FOR THE MACHINERY EQUIPMENTS.

Reduce the pressure on the live line

To buypass when you you have to work on component for example filters.

in my opinion is to bring a secure reliefe of over pressures in te systems