In a steady flow process a fluid flow steadily through a control volume. At any point, fluid properties remain constant during the process. There are many engineering equipments which function as steady flow system.
In a cyclic system, energy cannot be stored in the system. If all the heat cannot be converted to work and no energy can be stored, some of the energy received must be rejected.
In a reciprocating IC engine, the combustion of the fuel occurs within the engine cylinder. The engine partially converts the heat of combustion to work.
Safety valve is a Boiler mounting for safety against high pressure. Fusible plug on the other hand is another Boiler mounting for safety. But Fusible plug is a safety mounting against elevated temperature due to low water level inside the Boiler.
Safety Valve is one of the Boiler Mountings for safety. It protects the Boiler against steam pressure higher than the working presure.