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More ways to get Braingle...

Water Pump

Science brain teasers require understanding of the physical or biological world and the laws that govern it.

 

Puzzle ID:#3553
Fun:*** (2.61)
Difficulty:** (1.96)
Category:Science
Submitted By:Bobbrt*****

 

 

 



You have a 100 ft deep well, and your water pump is damaged and in need of repair. You hire two plumbers to quote you a new pump. One says that he will replace the existing submersible pump with a similar model for $200. The other says that he will sell you a high efficiency vacuum pump, which will cost you $50 less and will have the added benefit that you can keep it in your basement for easy maintenance instead of having to put it back down the well. Which pump should you buy?


Answer

You should buy the $200 submersible pump. A vacuum pump can only draw water from a height of about 30 feet, no matter how powerful the pump is. With a 100 foot deep well, the pump would not provide any water to the house. The second plumber obviously has no idea what he's talking about.
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Comments

(user deleted)
Jun 11, 2002

It just stands to sense---it is the correce answer
megan
Dec 20, 2002

Its a good one, but i thought it was not more than 10 m, [but i think its for another liquid, mercury?]
mcfarfar
Jan 21, 2003

why can a vacum pump only beused at a height no greater then 30 ft, no matter what?
Bobbrt**
Jan 21, 2003

When you use a suction pump, the maximum amount of vacuum you could pull is of course full vacuum. Since the bottom of the well is at atmospheric pressure (14.7 psi), 14.7 psi is the maximum pressure difference you could have between the bottom of the well and the top. I won't go through the math, but 14.7 psi is only enough pressure to push water up about 33 feet. To get water to go higher, you need more of a pressure difference. You can't get more pressure with a vacuum pump. You need to put a positive-pressure pump that can generate more than 15 psi at the bottom of the well. With a strong enough pump, you can push the water up as high as you want. I'm not sure I explained this very well, but I hope it helped. Oh, and megan, 10 meters is equal to about 33 feet, so you were right.
mcfarfar
Jan 22, 2003

it helped, thank you!
electronjohn*us*
Feb 13, 2003

Good teaser and answer Bobbrt! This one got me all pumped up!
Bobbrt**
Feb 14, 2003

To ElectronJohn: GROAN.... ;)
bluegrasssAus**
May 03, 2006

A shallow well vacuum pump can only pull maximum 30ft to 35 ft, but a deep well vacuum pump can pull well over 200ft. This is because it has 2 pipes going down the well. 1 sends water down to a Jet in the well creating a suction so the other 1 pulls water up to furnish well water. Since I have done plumbing and well work, your answer is only partially correct. I have help pull deep well vacuum pump pipes as deep as 375ft. So A deep well vacuum pump could also work, since there was no clarification on what type of vacuum pump was to be used.
cyberstar5150*us*
Aug 04, 2006

Very nice one!



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