Are they all made the same? Or are some more constricting than others? I just got a brand new Fusion 700 Air Pump rated to run 12 things off of it. And all of the instructions show with a check valve figured in to that equation. I put the check valves on just to run one small sponge filter and one small air stone (all in close range to the pump itself) and the air pressure is ridiculously low. I've checked the check valves under water and they aren't leaking. These are just cheap ones I got at Walmart so are there other brands that don't restrict the air flow as much? Without the check valves attached, yes this is a very powerful air pump that could definitely run a lot more on it. I got it to run 3 small sponge filters but there's no way in hell it will be able to do that with these check valves on.