how do self-filling/gravity fed pet water bowls not overflow and spill everywhere?
In: 276
Pretend they’re being sucked up at the same rate as they’re flowing out, so there’s an equilibrium. The negative pressure inside is sort of like sucking it back in.
Same reason when you put your finger over the top of your straw and pull it out of your drink, the liquid doesn’t pour out of the bottom of the straw. When you block the flow of air, air can no longer replace the space that’s occupied by liquid. This creates a negative pressure zone that essentially holds the liquid in place.
With a gravity water bowl, when the bowl fills up it also blocks airs path up into the tank. This is essentially the same as putting your finger over the end of the drinking straw.
The water in the bowl blocks any air from getting up underneath the feed and prevents any air from getting up into the container, so the water is held up be that negative pressure. Kind of like when you suck water you a straw and then can hold it there in the straw.
When the let drinks water, the water level lowers, allowing air up into the water container, letting you that pressure, letting some water out until the bowl is refilled.
One side (the jug) is sealed air-tight. The other is open to the atmosphere.
As long as no air gets into the jug, air pressure is only pressing on the bowl surface, not the jug. Any air-space in the jug is at lower pressure than the atmospheric pressure of the surface of the bowl, and cannot not push the water down.
Now, poke a hole in the jug. Atmospheric pressure will push in, equalizing the pressure in the jug with the outside of the jug…the water will settle to one level (ie. go everywhere).
The atmosphere is actually quite heavy. We just don’t notice because we’re used to it and are also pressurized from the inside. If you lie on your back, there’s around a ton of air sitting on your chest at sea level.
Those self filling pet bowls usually are just a bottle of water attached to a dish. The water runs out and air bubbles up inside of the container until the level of the water covers the bottom of the nozzle. At that point the atmosphere is pushing down on that puddle of water keeping it from rising and there’s no path for air to get inside the bottle. The weight of the water in the bottle is nowhere near enough to overcome that pressure so it stops flowing.
I forget the exact numbers but in order for the water to flow out of a 2-liter sized bottle, the bottle would have to be something like hundreds of feet tall or something (don’t quote me on that number) for the weight of the water to be enough to force its way out. Or, if you just poke a hole in the top of the bottle, the atmosphere can flow in from that side and then the water will in fact drain out to an even level.
The atmosphere is just that heavy. It’s shoving down on the surface of the water bowl at 14 pounds per square inch. The upside down bottle lets water flow out until enough water is in the bowl to block the bottle opening. At that point, air can no longer flow in and replace the lost water.
You now have a situation where 14 psi of pressure is pushing down on the surface of the water in the bowl and a vacuum being formed inside the bottle.
If you were to punch a hole in the bottle, air would be able to enter and fill the void and all of the water would spill out because there would be 14 psi inside the bottle as well as outside.
Latest Answers