You are right... that might or might not be an issue over time. Here
they sell check valves with a different design, might be worth to check out.
Those check valves sound like they work the same way, but they are not see thru so you can see how they work. I would imagine though that an residue buildup on the diaphram or walls will also cause that design to fail.
I got sick of using check valves on brine shrimp hatchers cause the salt water would cause them to fail after just a month or two and went to just puting the pump up higher than the hatcher water level to prevent a back syphon.