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Head pressure with pool pump

  1. Oct 22, 2016 #1

    DaveC426913

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    I have an above-ground pool which, tis the season for draining and winterizing. I have a 15 foot section of ribbed pool hose (designed for pumping) that I hook up to the pump and flush the pool with.

    Pool is 4 feet deep both inside and outside, with a 1foot lip.
    Hose needs to rise one foot from water surface over edge to get to intake.

    I only need about 5 feet to reach from the pool bottom to the intake, and the hose only needs to rise about a foot out of the water. (So my head is 1 foot right?) The other 10 feet of hose I tend to drop into the pool - with the rationale that I'll get better pressure than if it were lying outside on the ground.

    Is this true?

    If, instead I left the excess 10 feet of hose outside the pool - i.e. I ran the hose from the bottom of the pool (4 feet up), over the edge (another foot up), then down to the ground (5 feet down) in a heap, then back up to the intake port (5 feet), would that make any difference in efficiency?

    Head is still one foot (because the only thing that matters is the absolute distance from the surface of the pool to the intake.)

    Amirite?
     
  2. jcsd
  3. Oct 23, 2016 #2

    CWatters

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    Would a syphon work?
     
  4. Oct 23, 2016 #3

    JBA

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    The way I see it, if I understand the configuration from your description that he pump is located on the top edge of the pool, you are correct about the 1 ft suction head (but it is a negative head) and that is only only at the start because as the pool empties you will eventually reach a 5 ft negative suction head for the pump and it really doesn't make any difference whether the excess is inside or outside the pool, ie no advantage to placing it inside. On the other hand, as stated above, why not simply use the hose alone as a siphon without the pump. Alternatively, if there is a hose running to the ground connected to the pump discharge then this also acts as siphon and eliminates the negative head entirely throughout the draining process.
     
  5. Oct 23, 2016 #4

    DaveC426913

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    My goal is to maximize efficiency. A syphon - while it would drain the pool eventually - would take forever.

    No. At the bottom.

    Yes, the efficiency will drop as the water level drops. Still, looking for best efficiency overall.

    Because I'm mortal. :wink:

    Here are the two arrangments:

    pool2.png
     
  6. Oct 23, 2016 #5

    BillTre

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    The extra length of hose will add resistance to the flow.
    As the water level drops the head to the top of the pool edge will increase (as noted), however, your drawings indicate that, once full of water, the hose/pump system will act as a siphon, so no head.

    If you can extend the end of the tube outside the pool to a lower point it will act as a stronger siphon.. The increased pressure difference driving the siphon will add to the force of the pump.
    Otherwise, you could make the hose shorter to reduce resistance (probably a small change).
     
  7. Oct 23, 2016 #6

    DaveC426913

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    The only way to do that would be to lower the pump itself. Otherwise, any drop in the hose wil have to rise back up to the pump, negating any siphon-effect.

    (Besides, it's a 1/2hp pool pump. Any siphoning effect is figuratively and literally a drop in the bucket compared to its throughput).

    Yes, ideally, I would use a hose no longer than necessary. But the hose is dual purpose; it is also the cleaning hose, which means it needs to be long enough to reach the farthest edge of the pool
     
  8. Oct 23, 2016 #7

    JBA

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    If the pump is located at the bottom as you show then the inlet hose will act as its own siphon to feed the pump and since the only losses from the hose will be flowing friction related only to its length it makes no difference whether the extra hose is inside or outside of the pool.
     
  9. Oct 24, 2016 #8

    BillTre

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    The only other loss I can think of would be at the turns. They cause more resistance. Sharper turns make more resistance than more gentle sweeps.

    You could also consider labor expenses (what's easiest). In or out, probably a wash unless one means you have to make a lot of sharp turns. Just put the hose where its easiest to set up and will remain stable.

    Another issue might be what happens when the water gets toward the bottom.
    Pump will fail when too much air is drawn into the hose. How can that depth be minimized?
    The hose might also flail around when it is full of fast moving alternating blobs of low density air and higher density water.
     
  10. Oct 24, 2016 #9

    DaveC426913

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    True, though that's not a factor in the experiment. (I can adjust the radius of the loops regardless of which configuration I use)


    True in theory, non issue in practice. A pool should never be drained all the way when winterizing; it will collapse. I stop when there's 18 inches of water remaining.
     
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