I recently replaced a 1/2hp with a 1hp shallow well pump to increase my output. I had a Brady 1-1/4" check valve in the horizonal position just in front of the pump. I changed the check valve to one that had a larger hole to help with less restriction to the pump . Now I keep loosing prime in less than an hour after shuting down the pump. When I took the check valve loose, I had a vaccum behind the valve which indicates that the check valve was working. Any ideas as to why I am loosing prime?