I was recently surprised to see some tank designs that included dual vent devices (dual PVRVs and ERVs). The client claimed they needed installed spares in order to be able to pull one for inspection/maintenance (similar to the practice with PSVs). When I mentioned that it's not standard industry practice to install dual tank vent devices, the client asked how can you safely perform inspection/maintenance without having an on-line spare.
i couldn't answer that question, other than to say that there are obviously safe ways to do this without having an installed spare - I just don't know how it's done. If that weren't true, then installed spares would be common.
How is tank vent device maintenance done in your company?
Thanks