Question
I prime my pump.Run my sprinkler sys.1.5 hrs.It will hold 40psi overnight.And the first time I use it in the mourning .It loses prime.I use to use pvc check valves recently went to brass.FRANK

Answer
Hi Frank

If the pump loses prime you have a leak between the pump and the water source. If you recently replace the check valve check for leaks at the male adapters. If you don't use teflon tape this will cause a leak an get air inside the pipe. If you have a hose bib at the pump make sure is completely closed. If there are no leaks probably the screen canal is broken and allows dirt get in and keeps the check valve open in this case replace the screen canal.

Regards
Guillermo