Let's see...in my car wash that I owned for six years, I had hundreds of check valves, everything from tiny plastic ones on ¼" poly lines, to large stainless steel ones on high pressure lines (2400 psi).
My guess is you don't want any kind of spring valve in there, since they require a certain "cracking pressure" in order to open and function. In your application here, you need to be able to deal with low flow and low pressure and full flow, and a swing is the one to use. At the car wash BTW, all the checks had a relatively short life and I had a shelf full of spares, and was constantly rebuilding the high pressure ones. It was just what you did at a car wash.
That doesn't solve your issue. Try replacing with a different brand of swing. Maybe a different one will last longer. Maybe stainless steel. I cannot tell what size piping you have there, but assuming its ¾", a ¾" stainless swing check valve on Amazon is less than $15.
What the hammer solution is telling me is that the swing isn't opening until you hit it. Something's holding it up.
If this is a constantly recurring thing, I'd replace those SharkBites with unions to allow for easy replacement. There's only so many times you can open a Sharkbite before it will fail; they are not made for repeated use.
