Aquarium Air Pump Check Valves Plastic One Way Non-Return, Black

It wasn't clear to me from the pictures here how these work. I thought the rubber thing inside moved around but that isn't the case. The rubber thing is hollow and has a slit on the end that closes with suction and opens with pressure. They do block suction well but the entire thing can leak because the threads don't seal. And the back pressure is rather high, much higher than for a free ball type seal. Lots of mold flash doesn't help sealing. And mine weren't assembled well, I had to unscrew the top and push the rubber thing all the way down onto the hollow post. For aquarium use consider doing this and then sealing the threads with silicone caulk or rubber gasket, or similar. I wish they'd put more effort into making a couple work well than in providing a ton that barely do so and need work.

I got these as they are barbed to keep the airlines from falling off. That part works great. But the manufacturing process is lacking, lots of quality control issues, check that each one passes air before using. I find about 1 in 4 doesn’t work at all, the rest are fine.

These worked better than the other ones I have used this is my preference I'd say give them a try

I like these check valves much better than many others i have tried as they flow freely, seem to work really well.

These are way better because you can service them. Just twist them apart squeeze the silicone tip to clean. Put back together and run them.

Was happy to see these in black instead of the usual red ones. Have used just one so far without any problem. Just make sure you blow into it to test it out & install it in the correct direction. Didn’t actually need 20 of these things so now I probably have a 5 year supply. Hopefully my fish will live that long!