I have a stenner pump for adding acid to my pool. The check valve just recently seized on me. I confirmed it was pumping fine until I hooked up the check valve - with the check valve on, nothing was getting through. So, I got replacement - exact same valve, verified it worked on the stenner pump. Now the acid can get through. But - when I screwed that to the PVC pipe and turned on the pool pump, it started to leak. The water was coming out of the actual valve - so through the check valve. (I don't even have it connected to the Stenner. I put my finger over the end and I could feel the pressure slowly build. I assume that should not happen at all. Did I get a bad valve? Is there any tweaking on these? It seems pretty simple.