Originally Posted by 1idejim
How's that work?
Posted via Mobile Device
They're set up in parallel to each other, and the smallest one alone delivers low flows, and has the highest outlet pressure. The outlet pressures of the additional PRVs are lower, by steps, so they open one at a time as flow demand increases.
What you get for the extra work, is avoiding the seat wear that happens sometimes when a small flow takes place over one portion of the seat of a larger PRV that isn't even beginning to open fully. Over a small enough seat area, the small flow can be at a velocity that can erode the seat material.