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Old 04-13-2013, 12:18 PM   #1
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ground water sump pit water flow


Why wouldn't this work? If the ground water that flows into my basement sump "pit" from a pipe in the foundation around the house was one connected pipe, from where the ground water enters now, before it gets to the sump "pit", to where it exits now, (up and out vertically, via the sump-pump motor), just as well be directed up, and out and away from the house without using an AC pump motor or battery back-up system? Why wouldn't the "water" in the continious piece of drain pipe continue to rise inside the pipe vertically until gravity takes over and is directed out and away from the house and foundation above grade? I tried it with a piece of hose, with a 90 degree bend in it, and the water kept flowing from the top of the vertical run as long as the entire length of hose was filled with water. (otherwise, it would have been air-locked right?)
What am I not understanding? Not enough water pressure to force the water vertically? Blow-out eventually from the entry point? Didn't the Roman's aquaducts raise water over long distances this way by flowing and rising water reaching it's own level and then gravity drops it? During storms, AC sump-pumps and battery back-ups fail, thought I'd ask an expert about this! It just struck me that if the sump "pit", just continued up the wall and above grade, then the water inside would spill out, but outside through a pipe and not flood my basement anymore.
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Old 04-13-2013, 02:46 PM   #2
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ground water sump pit water flow


You are not understanding the fundamental physics of water flow. Water always flows from higher total energy to lower total energy. The energy of a cubic foot of water is derived from a combination of elevation, pressure, and flow rate. For groundwater, flow rate is very low, and the pressure at the surface of the water is atmospheric, which is typically taken to be zero.

Therefore the total energy of a cubic foot of groundwater is equal to the elevation of the groundwater. You want to pump that groundwater up and away from your house, so you need to add energy to it, which is why the pump is there. If the groundwater was pressurized sufficiently to flow up and to the street, your entire house would be under water. So generally you need to add sufficient energy to the water to raise it from basement floor level to street level, plus some energy to handle friction losses in the pipe and in the pump.

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Old 04-13-2013, 10:59 PM   #3
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ground water sump pit water flow


A siphon is an upside down U shaped tube through which water will flow up and over so long as the tube is filled with water. The direction of flow is always from the side whose water surface is higher.

If the destination side simply disposes of the water (is not a pool) then sooner or later all the water on the source side is used up and air goes up into the siphon and the flow stops. Should more water accumulate on the source side the siphon will not resume flow until it is refilled, either manually or using a pump.
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Old 04-13-2013, 11:25 PM   #4
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ground water sump pit water flow


In two words - hydrostatic pressure.

Unfortunately no house is water-tight from its basement floor up to where it's foundation clears ground level. If it was then your thought process might have more merit to it; then again if it was you wouldn't need french drains or a sump pump. :-)

It would take an incredible amount of pressure to build up in order to force the water through your drain tile and up 10' or so. Long before this the hydrostatic pressure would defeat your basement and force its way in via cracks and other imperfections. Water is lazy yet very powerful.
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