I've attached a video of two of the check valves not working. You will see a bag full of a green liquid and a bag of the clear water both connected to a Y-connector and then through a peristaltic pump and then into a separate container. The clear water is connected using a check-valve placed in the correct direction (so it should allow water to flow freely to the container on the other side of the pump), the green fluid is placed such that the check valve should block all flow through the pump and into the chamber. The pump was run for about 20 seconds, and, as can be seen in the video, the clear water flows much more freely through the pump than does the green fluid; however, enough of the green fluid is getting through to give the water in container a greenish hue You can also see that even to the left of the check valve the clear part of the tubing contains some of the green fluid. In addition, after leaving the setup alone for about 3 minutes, the green fluid had leaked through significantly and back into the clear water bag, going against the direction of both of the check valves.
