I use Zoeller check valves with the rubber boot/SS banded clamps. Has the flap inside of it. I've never needed a gate valve or union. I have seen them installed on some applications, does make it easier to switch out a pump easier but most times the valves are jammed open, the unions will break down only if someone used grease or sealant to allow the union to unscrew. Most times those unions will "glue" themselves together because the O-ring inserts will flatten, allowing the connection to leak. I just replaced a O-ring on a water softener for the same exact reason; rubber was flattened from the years of being compressed.