I too just built a 2 tier hermes system, hard piped. All 1/2 in copper. zero problems with priming. my pump (1 of 2 LG 3-hc-md ) is at the lowest point in the system. The first output in my outlet manifold goes to a 1/2 id hose via hose barb. It drops to below the pump and to the front of the stand. DO NOT restrict on your inlet side of your pumps. For my inside sculpture i switched to 5/8 ID hose on the inlet side. If the smallest diameter is on the inlet side of your pump, you will ALWAYS have priming issues. There should be little reason for one of these valves IMO.