Help with gas lines

I am having trouble with my gas lines! Wondering if anyone can tell me why I am getting three different pressures out of my 3 way manifold... I took everything apart and let air through it was fine but then I put the check valves back on and one lets almost no air through another lets just a little more through and the third seems to be fine letting it blast through...and yes I made sure they were open while checking...Did the check valves get ruined? What did I do? I didnt see anything wrong with them visually