Wednesday, October 01, 2014
Why Can't a Water Pump pump more than about 9 meters?
Q: Even with larger and larger pumps the engineers were confused as to why they couldn't pump deeper than about 9 meters deep, why?
Hint: The pump they used was at the surface and brought up water via suction. Why is that important?
Hint: I they placed the pump at the bottom and pushed the water up, it worked at greater depths.
A vacuum is just the removal of the air that exists everywhere, so now there's a pressure difference between the bottom of the well (the air pressing down on the water) and the top of the tube where the vacuum is.
The pressure (at sea level) is about 76 cm of mercury. This is how much it could push. The weight of mercury vs water is about 13. So 13.5 * 76 cm is a little more than 10 meters. But you can never get a perfect vacuum and the water at the surface would start to boil, so the best you could do is about 9 meters.
Hint: The pump they used was at the surface and brought up water via suction. Why is that important?
Hint: I they placed the pump at the bottom and pushed the water up, it worked at greater depths.
A vacuum is just the removal of the air that exists everywhere, so now there's a pressure difference between the bottom of the well (the air pressing down on the water) and the top of the tube where the vacuum is.
The pressure (at sea level) is about 76 cm of mercury. This is how much it could push. The weight of mercury vs water is about 13. So 13.5 * 76 cm is a little more than 10 meters. But you can never get a perfect vacuum and the water at the surface would start to boil, so the best you could do is about 9 meters.
# posted by Scott Kirkwood @ 8:30 AM 
