What is the purpose of duplex strainers in a fuel oil system?

Duplex strainers are designed to ensure the continuous operation of a fuel oil system while allowing for maintenance tasks, such as cleaning or replacing strainers, to be carried out without interrupting fuel flow. This dual design—where one strainer can be taken offline while the other remains in service—ensures that the system does not experience a shutdown or loss of efficiency during maintenance.

The other options focus on attributes that duplex strainers do not primarily address. Improving fuel efficiency relates to optimizing combustion and engine operation rather than the filtration process itself. Regulating fuel flow involves control mechanisms, which are separate from the straining function. Monitoring pressure levels typically refers to pressure gauges or sensors, not to strainers, which serve a different purpose in filtering out particulates from the fuel. Therefore, the function of duplex strainers is specifically to maintain operational continuity during maintenance, perfectly aligning with the correct answer.