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This question was originally posted on physics.stackexchange.com and then moved here since it was off-topic there


We rely on submersible water pump for household water supply and there's too much silt that keeps blocking faucets, collecting in tubs & buckets etc. Based on someones's suggestion I recently got a local plumber to create this simple setup involving two PVC tanks to leverage sedimentation for cleaning water.

overflow water supply setup with PVC tanks

Here's the brief explaination

  • Submersible water enters the left tank from top, then moves to right tank from bottom connector (placed about 3 inches above the base of tanks) and eventually exits from it's overflow outlet into the main tank below.
  • As you would imagine, when the pump is switched on for the first time, both PVC tanks would get filled upto the level of overflow outlet from 2nd tank, and then will forever remain filled until manually drained.
  • Capacity of both PVC tanks is 300 litres, but since overflow outlet is placed about a third way from top, I expect both to hold roughly 220 litres of water in steady state.
  • There are no specialized filters, gauzes, membranes etc. placed inside the tanks, they are completely hollow but sealed shut from top.

My expectation is that

  • Left tank would primarily serve the purpose of arresting turbulence in water flow besides collecting heavier sediments
  • And right tank would then further settle lighter particulates (lighter than those collected in left tank) at the bottom due to simple gravity separation as cleaner water would calmy rise and exit from overflow outlet.

Please understand that

  • While there are special industrial grade meshes and filters, scrubbers, domestic-use softeners etc. that can do a far better job, but in my area and home those are infeasible and I specifically needed a very low maintainence solution.
  • Based on my daily water consumption and amount of sediments, anecdotally I estimate that these PVC tanks would require cleaning once every 12-15 months only.

My questions are

  1. Would this setup be effective in removing particulates as I expect? Is there any obvious flaw in the setup that I overlooked?
  2. Could a different configuration of connecting or placing the tanks etc. have given a more effective solution? (assume we can use upto 3 PVC tanks of any capacity as long as total weight of water remains under 500 kg)
    • by different way of connecting I mean for example say connect bottom of left tank to mid of right tank
    • by different placement of tanks I mean say one putting one tank at a higher level than other
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  • We had 4 tanks which were sand filters and inlet at the top with outlet at the bottom. Not sure yours are well designed, if your outlet is low then it can draw in sediment as it settles...
    – Solar Mike
    Feb 17 at 16:25

3 Answers 3

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I wouldn't draw from the bottom of the first tank; that defeats the purpose by drawing the most sediment laden water. Seems to me you want both flowing upward. Ideally with some centrifugal separation as well.

Remember to have a drain tap at the bottom to periodically flush accumulated sediment.

Frankly, a real filter (with backwash setting to clear it) feels like a better bet, though you might need a booster pump if flow is already low.

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  • Note; one down and one up might make sense if some of the crud is expected to float and some to sink. But if the water's that messy I don't think settling tanks would be adequate.
    – keshlam
    Feb 18 at 6:17
  • My assumption was that keeping left to right tank connector on top would result in higher percentage of sediments moving over to right tank (unless the left tank was several feet wide) since when pump is turned on the incoming turbulent water stream would shake up things. That bottom connector b/w tanks is placed 2 inches above the tank-floor, so I thought heavier sediments should still settle. Moreover even sediments that manage to move to right tank would likely not 'rise' up to the level of overflow outlet since they are heavy and by that time water's turbulence is arrested Feb 18 at 19:12
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Inflow to both tanks should be tangential and at the top. Outflow from both tanks should be central and at the top. That's employing vortex filtration by spinning the water in the tank, so the sediment flows outward and falls down, while cleaner water collects in the middle.

I find it dubious that (even if you had to import it) one of these filters (which combines centrifugal flow filtering with a screen and an area to trap collected sediment that can be flushed) would cost more than multiple large tanks, but if you want the most benefit of multiple large tanks, replicating what these do as closely as possible will do that.

enter image description here Image Source no endorsement implied. I do use a similar filter myself, for which I paid full price and have no other relationship with the producer. It gets the solids out of my incoming water in a very compact manner.

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This seems like it would work, assuming your water flow speeds could remain low enough. Some alternate options that are commonly used in industry are a horizontal flow sediment tank, and a tank with inclined plates. In both of these systems, the output will take the form of a weir rather than a fitting.

If you plan to do this system, I would set it up to use a weir from the first tank to fill the second tank, then a weir from the second tank for outputs. You will have to put a pump between the two tanks and for the output of the second tank in order for a system like that to work, but it should be more effective at removing sediment.

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