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Q & A: Float type water cut-off valve.

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Most recent answer: 07/25/2011
I have a pipe with 65psi of water flowing into a tank with a ball float on the end of the pipe that is essentially a 1.5 inch ball at the end of the pipe that floats up to close the water coming out of the pipe. How deep in the water does the ball have to be to have enough pressure forcing it upward to hold back the water coming down the pipe?
- John Williams (age 71)
United States
Hello John,
The answer depends mainly on the diameter of the 65 psi inlet pipe.   The amount of force needed to stop the flow is 65psi times the area of the pipe  F = πd2/4.   If the inlet pipe is 1.5 inches in diameter that gives F = 36.5 pounds.  That's a bunch.  If so you would probably have to go with a levered system, much like that in a flush toilet.     For smaller diameter inlet pipes diameters the force would be much lower. 
For the record, the buoyant force is the displaced amount of water, in cubic inches, time the density of water,  a cubic foot of water weights 64 pounds.
Let us know some more details.


It doesn't sound like it works with that 1.5" ball float, unless the hole is much smaller. / mw

(published on 07/25/2011)

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