Skimmers - Pump head height Theory?

Discussion in 'Anything DIY Related' started by lIghty, 6 Apr 2010.

  1. lIghty

    lIghty

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    Ok, just want to though a bit of "theory" out there and see what the scientists have to say, it all about water levels, head height and "vacuum" pressures.....

    He's my thoughts........ but first an illustration to show what I'm talking about.


    [​IMG]
    Hope this makes sense?????:whistling:

    With the internal unit, the pump supplies the both the internal water level (WH) and well as the air sucked though the venturi (AH), now this is a balancing act, since if the skimmer sits in deeper water the head height (WH) decreases (water flow increases), BUT more vacuum is require to suck air down deeper into the water and therefore air flow is decreased due to the (AH) height increased, and visa versa.

    By the nature of how a venturi works, to more water flow thought it, the more air it suck, so how do we calculate the best level to get the best ratio? Is the relationship between the two linear?


    With the external unit, there is only one factor, AH, this is basically determined by the height of the skimmer. There is no actual water head height on the pump, since it form a closed loop. Only the supply pump has a head height to pump, but this doesn't affect the system.

    Now here a idea.....:whistling:

    What would happen if we moved the circ pump closer to the surface, is would reduce the vacuum AH need to pull the same amount of air into the pump, but it would create a new obstacle, the pump would now have to force the air down wards to the bottom of the skimmer, which is below water level......:whistling:



    [​IMG]




    And now for another question, how do you calculate the maximum air flow through the pump without it starting to cavitate?

    Any comments? (PLEASE, I ASK TO KEEP THIS STRICTLY ON TOPIC, IT'S A CONFUSING ENOUGH TOPIC ALREADY, THANKS)
     
    Last edited: 6 Apr 2010
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  3. Neil H

    Neil H Moderator MASA Contributor

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    interesting concept here .......

    would placing the pump half way up be the best... option? which is harder pushing air or water ? maybe that ratio is the key?

    how does the latest cone shape influence this theory ???
     
  4. lIghty

    lIghty Thread Starter

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    Well, its really pushing air (with water) or pulling air down into water.

    It doubt the ratio between the 2 are linear, but who knows, it might?

    The cone shape wouldn't effect it, as that wouldn't change the head height, only the surface area.
     
  5. RiaanP

    RiaanP Moderator

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    I think the pull of the air via the venturi is free. The water rushing past the venturi creates a pull action, that sucks air down.

    But with pump lifted, then you have to blow the pulled in air, down the pipe with water, creating or re-combining air bubbles. And by the time it enters the skimmer chamber, a lot of the very fine bubbles will not be fine any more.

    But maybe I'm totally wrong...
     
  6. lIghty

    lIghty Thread Starter

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    I don't agree with the first part, the pull of air is not free, since you have to overcome the pressure to displace the water out of the airline tube. Think of it like this, when you skimmer is off, the airline fills with water to the sump level, this is the AH on the internal skimmer illustration.

    Second part I agree with, I also feel the bubbles will start to "re-combine", but will it be to the point that it would have an ill effect on the performance, after all, the velocity at which the water travels at it would have very little time?
     
  7. Neil H

    Neil H Moderator MASA Contributor

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    have the small bubbles not already done their job by that time, i.e. picking up the waste particles .... take a bubble plate ..... the first thing it does is to start combining the bubbles into larger bubbles by virtue of it slowing the bubbles down?
     
  8. RiaanP

    RiaanP Moderator

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    A bubble plate will not keep the bubbles together like a 400mm piece of tubing will. Not gorgetting about the bends. But maybe I'm wrong.

    But my logic says that you want the hardest, strongest flow into the skimmer. The stronger, the stronger the venturi pulling power. Any bends will give back pressure.
    Strong inflow, strong venturi, a lot more bubbles enter.

    And as water passes the venturi inlet, the laws of nature steps in pulling more water from the venturi until it is empty and pulls in air. I doubt if the pump need to do any hard work here. What you could do to get more in is, is to use a thicker pipe for venturi inlet.
     
  9. jacquesb

    jacquesb Retired Moderator

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    Justin - this is indeed a very interesting topic. I agree. Please people -(those who has not yet posted). No banter. It will be deleted.

    That said - I have always believed that forcing air into the skimmer pump does assist with increasing the air intake.

    So - I want to give you a different take on this:
    Why worry about the actual height of the pump, if you can rather just get a blower to force air into the skimmer inlets to make the skimmers far more sufficient?
    The the amount of air "sucked into the pump" becomes invalid?
     
  10. Neil H

    Neil H Moderator MASA Contributor

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    Interesting point there JB, BUT if we take say a TS2 and inject another 500L ph of air alone, how would the skimmer body hold up..... one assumes that it is designed for a certain amount of air and water entering into the chamber, if we were to up the air proportion how would this affect the skimmers performance

    how do they rate skimmers by the amount of air injected or the throughflow of water or a combination of both ?
     
  11. jacquesb

    jacquesb Retired Moderator

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    I would love to have Tony from D&D and Zain's input here.

    I too would actually love to know.

    When I had my TS2's, I actually wanted to upgrade my OTP-2000 pump to an OTP-3000 pump (needlewheel at the time). But, never did this. I was not sure of what the impact would have been, though.

    Now - seeing that you started with this, Justin:
    I have a seen a monster DIY-skimmer, where the recirculating pump was a Speck swimming pool pump, but, there were 2 x Beckitt air-valves on the skimmer.

    What are the true differences between using a venturi-type air-valve, and a beckitt-airvalve?

    W.r.t the skimmer body - my personal opinion is that the skimmer amount of air would not make any difference to the actual skimmer body (like in "breaking the body"). But more perhaps with the length / width of the tube, because of the amount of air injected - you might not get the right amount of water to mix with this amount of air.

    So - I THINK that it is a mixture of the amount of air and water.

    That said - I successfully "modded" my TS2's that they produce a lot more skimmate, by forcing air into the 2 skimmers, using a pond air-pump, which supplied 17 litres of air per second (1020 litres of air per minute), into the skimmers.
     
  12. lIghty

    lIghty Thread Starter

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    WRT a bubble plate, I believe it would increase flow rate inside the bubble plate chamber and while exitting the camber, the reason: same flow rate coming in from the pump now into a smaller chamber (bubble chamber) and as it exits the chamber though the smaller holes, they ack like jets (reduced cross sectional area) and speed the flow up further untill they reach the main chamber where they slow down.

    But venturi's are designed for certain criteria (flow, pressure, etc). The venturi does the work to form the vacuum/suction to pull the air, but there are limits to the vacuum any one venturi can form. An eg: in you sump the pump/venturi sucks air down into itself, but the water is only say 200-300 deep, extend the air pipe to 2m and chuck it into the deep end of your pool, I doubt it would be able to suck the air down that far, its due to the pressures.

    This is true, but it create a new set of posible problems, as stated in my above post.
     
  13. jacquesb

    jacquesb Retired Moderator

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    Many thanks for your input Justin. Then I am still wondering - why not just use an "air blower" and decent sized pump, instead of worrying with a venturi air-valve?
     
  14. lIghty

    lIghty Thread Starter

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    I think its not just about pumping air into the skimmer, its about finding the perfect air/water ratio that a perticular skimmer performs best at? because I agree, you can put too much air, Balloons don't remove proteins:whistling:


    Did it not cavitate with so much air?
     
  15. lIghty

    lIghty Thread Starter

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    Would work, maybe even easier to tweak to get top performance.
     
  16. jacquesb

    jacquesb Retired Moderator

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    Hi Justin - no. Mine never cavitated. I have some pics in my old thread. Let me see if I can find it. As I said - it worked very successfully.....
     
  17. jacquesb

    jacquesb Retired Moderator

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  18. lIghty

    lIghty Thread Starter

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    Ok, so the Beckett air-valves is just a venturi that works on the "high pressure" side of a pump.
     
  19. jacquesb

    jacquesb Retired Moderator

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    Jip - BUT, I believe that the beckett air-valves are far more efficient than "normal venturi's".....
     
  20. lIghty

    lIghty Thread Starter

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    I would agree due to thier design, there is less restriction
    Posted via Mobile Device
     
  21. shane

    shane

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    These beckett venturi's work on high pressure water as you said earlier Justin, but now you have to run bigger more powerfull pumps which require more electrical power which equals more rands out of your pocket.
    Cheers
     
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