Which service valve should be installed to isolate dual pressure relief valves while keeping the system in service?

A three-way valve is the appropriate choice for isolating dual pressure relief valves while keeping the system in service. This type of valve allows for multiple flow paths, enabling part of the system to be isolated without shutting down the entire system. When installed in a configuration with two pressure relief valves, the three-way valve can direct flow away from one of the valves while maintaining operation through the other.

This functionality is crucial in various industrial and safety applications, where it is important to maintain system pressure and safety features while performing maintenance or testing on one of the relief valves. The design of the three-way valve allows one outlet to be open while the others can be closed, thus providing the necessary isolation without disrupting the overall function of the system.

In contrast, other types of valves like two-way valves do not offer the required functionality for this particular situation, since they only provide a simple on-off control without allowing for multiple flow paths. Four-way and single valves would also not meet the needs of isolating two relief valves while keeping the system operational as effectively as the three-way valve does.