We just had our existing well sprinkler pump replaced with a Red Lion 97101501 RL-SPRK150 44 PSI Cast Iron Self-Priming Lawn Sprinkler Pump. The vendor also replaced the check valve (not sure the brand but it is metal verses plastic), the zone valve with a K-RAIN 4404 4000 Series Indexing Valve with 4 Outlets and 4 Zones, and all the PVC from the check valve to below the ground under the zone valve. The issue is that sometime between 12 and 24 hours of the pump being off, the pump loses prime. The check valve was tested before installation. I believe the issue is related to how the plumbing between the pump and zone valve was done. It appears an alignment mistake was made and instead of the PVC coming straight out the pump and across to the zone valve as was previously done and is the way every other sprinkler system I have every seen is plumbed, the vendor plumbed the pipe up out of the pump to down under the ground, across about 12” then back up about 3’ and turned left going into the zone valve, essentially creating a big “U trap” between the pump and the zone valve. I believe this is creating an air lock and the reason the pump loses prime after 12 hours. Also the height of the pipe above the pump where it bends to head underground is higher than the zone valve. I attached a pic for reference. Assuming the check valve, or debris in the well or the pump or zone valve, and plumbing connections are not leaking or defective, can anyone please explain why the pump loses prime and if this weird “U trap” plumbing is the issue?