Today I got a new refrigerator carbon water filter (this). Before installing, out of curiosity, I dripped a bit tap water into the filter’s outlet to see if water could flow in and out. Obviously it did… Then, distracted by something else, I put the cap back on the filter and walked away. Several minutes later I heard a fairly loud pop sound. The cap popped out. So the filter must have been building up air pressure inside. I wonder how. Does it have anything to do how activated carbon interact with water? Any ideas?
The filter may have come from a cooler environment, so the higher ambient temperature caused the air to expand that was inside the filter as the temperature equalised..
As you had sealed the inlet & outlet with a cap then the pressure increased until it overcame the friction holding one of the caps.