Spidey wrote:Anybody that understands fluid dynamics can understand how gasses can flow “up” a downstream water flow induced by gravity. You can easily demonstrate this with a strobe light directed at an open faucet…notice that water doesn’t flow as a contiguous stream, it’s broken into droplets, and there are gaps between those droplets, those gaps can allow gas to travel against the stream. You also must understand that a gas trap is only fully effective when the water is standing still, very hard to calculate the effect when there is as much turbulence as there is in a toilet flush.
Like you said, anyone with an understanding of fluid dynamics would know that if any fluid is going one way, especially if fed via pump or gravity, would know that gasses would
not flow up the pipe. It's physically impossible. What happens is the ambient gasses (the air you breathe) gets sucked in through the bowl due to the fact the water level drops pretty fast. But what you say about the gas trap only being effective when the water is still (providing a positive seal) is absolutely true.
If gas were to go up the stream, that means the other end is capped.
As for the water breaking up into droplets, that's our friend surface tension at work.
Here's a (rather extreme) example: A hydroelectric dam. When they let the water through, either to generate electricity or to drop the level in the reservoir, do you see any bubbles on the inlet side? Nope. That's because gas, being lighter than liquid, is forced out from the outflow. Try it sometime. All you need is a syringe, and a tube. It doesn't even need the plunger.
Physics is fun, and there really is a fair bit of science behind the lowly loo.
