Check Valve not working?

[foxngn]

I don't know why does this happened, this is my 2nd check valve already, been tested with the check valve confirming that its only 1 way out & another way blockage. But when i plug in together on my co2 unit, the water from the bubble counter still able to backflow pass through the check valve.

Also i had placed the check valve above water level.

[Shadow]

It is normal if you are using those cheap plastic check valve. Get those metal check valve much better.

[foxngn]

aiya...cause the first one i'm using is Ista brand, it still passed, then use this normal plastic also passed.

Metal type, is there any brand to recommend?