How can you determine if a water pressure reducing valve has a bypass feature?

Question

Some states require an expansion tank installed with a pressure reducing valve with or without a bypass feature. California State code is not specific on wether this creates a closed system. I would like to know if the Uniform Plumbing code is more specific on this matter?

Answer 1

Are you talking about a pressure RELIEF valve or a pressure reducing valve?
If the former, it is generally located on the top of the tank and has a pipe coming out of it. The pipe does not connect to anything on the other end, but is either allowed to drop down to near the floor level, as on a hot water heater, or may be piped vertically through the roof or out through a side wall if the material in the tank is under higher pressure.
Perhaps you have a line entering the expansion tank from a city water supply and you are referring to a pressure reducing valve which lowers the "high" city water pressure of 50-75 PSIG down to a lower 15 PSIG in a low pressure heating system. If this is the type you have, a bypass feature would allow you to manually open/close a hand valve to add to the expansion tank level ONLY when needed and the automatic valve is not functioning.
Your questions need to be more specific and give full information or a photo or diagram of the installation to fully identify the intent.