Posted 05-31-2004 at 08:43:09
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In response to "Technical Question" posted by Joe.....
Concerning the pressure a pump would have to produce at the bottom of a 500 foot deep well to produce 50 psi in his storage tank.
Joe, there are numerous places on the `net and in books where you can find the weight of a cubic foot of water, it is generally accepted to be right at 62.427 pounds per cubic foot.
Since that is equal to a container 12 inches square and 12 inches tall, you can divide the weight of that cubic foot of water by 144 to get the weight of a column of water one inch square and 12 inches tall.
So, a water column one inch square by 12 inches tall would weigh .4335208 pounds.
That means a water column one foot tall, of any diameter, produces a pressure at the bottom equal to .4335208 pounds per square inch.
Multiplying by 500 gives a pressure at the pump of (.4335208 X 500) = 216.7604 pounds per square inch.
Adding another 50 psi because you mentioned 50 psi in your tank, that means the pump would have to produce 266.7604 PSI.
That is at static pressure. As soon as you speak of the water moving, then you have to add more pressure (at the pump) to overcome the friction of the inside of the wall of the pipe that would tend to inhibit the flow of water.
Someone also mentioned the water level in the well above the pump. You would have to take that into consideration too. Effectively, the height of the water in the well above the pump would need to be subtracted from the effective water column height inside the pressure pipe above the pump.
What that means, is if the well was 500 feet deep, and the water in the well was only 100 feet below the surface of the ground, the height of water column above the pump would effectively only be 100 feet.
In a static (non moving) water column (pipe) the diameter of the pipe has no affect on the pressure per square inch
Total pressure, yes, but, pounds per square inch, no.