Does the order, relative to the direction of the water flow, of reducing and relief valves matter in a pressure reduced subsystem (hydronic boiler in this case)? In other words, does it matter if the water comes in from the reducing (picture left) or from the relief valve side (picture right)?
That is a combination PRV and relief valve made by Bell & Gossett that was common many years ago. Today, the boiler code people prefer that the relief valve be mounted on the boiler proper. In fact, with a commercial or industrial boiler or pressure vessel that is mandatory in most states. That said, for your control, the one with the adjustment screw goes first so it can control the boiler pressure and the relief valve, the one with the handle on top, goes toward the boiler as the safety device. When using this type control you must make sure that there is no isolation valve between the relief valve and the pressure vessel. Hope this helps.
