lets talk skimmer water depth height

Discussion in 'Protein Skimmers' started by Dingo, Jun 21, 2011.

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  1. Dingo

    Dingo Giant Squid

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    wow this is very interesting! so a skimmer is actually using less energy AND being more efficient when its in a lower depth! I am going to add a riser under this tonight to bring it back up to what it was at before...
     
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  3. ComputerJohn

    ComputerJohn Panda Puffer

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    Pumps failing does suck, but I always recommend having a backup. You never know, especially on your return pump.. I have a backup for all my pumps. You know it's going to fail at a bad time. Plus having a backup the chance of it failing goes down, it always does.. ;)
     
  4. evolved

    evolved Wrasse Freak

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    Using less energy, yes. Being more energy efficient, yes. Performing more efficiently? Not necessarily. ;) The manufacture does have a recommended depth for a reason.
     
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  5. Powerman

    Powerman Giant Squid

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    Evolved, you are usually pretty good at this stuff, but this is just plain false in many respects.

    Head, as it is commonly used, is really "net positive head", and that is only the amount of hieght a liquid must be moved above the liqiud level. Head pressure is actually figured out by how deep the water is, and how high it has to go.... water depth adds to suction head and helps the pump.... if total hieght to be pumped is 6 feet, but the pump is sitting in a 3 feet of water... 3 feet of suction head from 6 feet of discharge head give a net positive of 3 feet of head pressure. A pump sitting in 6 feet of water, that pumps the discharge to the suface of the water has zero head pressure.

    Atmoshperic pressure is exerted on everything. It is often left out of calculations because it is a net of zero. 14.7 PSI absolute pushing down on the suction side, 14.7 PSI absolute pushing down on the discharge side, results in a net of zero. If a pump was sitting in 3 feet of water in an open container... and had to pump 3 feet up into a closed container with "zero" psi absolute..... then the head would be expressed as a 14.7 psi of suction pressure... that would be added to the pump discharge pressure for a total of "x" psi discharge pressure.

    Submersible pumps do not have a max submersion depth, they have a max cutoff height...which is the highest column of water it can support above the water level... the point at which it can move no more water.

    Head pressure does not use more power. Added head pressure uses less power. Power is determined by how much water is mover... or how much actually work is performed. The higher the head pressure, the less water moved, the less power used. A valve is no different than adding head pressure, restricting flow. throttling a pump reduces power use because it moves less water.

    Last, skimmer head is determined by how much water is ABOVE the waterlevel in the skimmer. More on that....
     
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  6. evolved

    evolved Wrasse Freak

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    Looks like I have too much pressure in my head today. I'll let the better-suited guy continue...

    (sorry for the wrong turn)
     
  7. Powerman

    Powerman Giant Squid

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    So this is how it works Dingo.... when you raise a skimmer out of the water, you have more room above the water level inside the skimmer..... while it is not all water, it is foam, it has weight, and it does exert a pressure. Raising a skimmer out of the water, increasing the amount of weight the pump has to hold above the water level, puts more back pressure on the pump, it reduces how much water it can move, it reduces how much air can be pulled, it reduces how much power it uses, it makes skimmate more dry because the foam has longer to drain.... and you will have to close the outlet more to keep the water level where it should be in the skimmer.

    Lowering a skimmer does the opposite.... less back pressure, more water flow, more air draw, more power consumption, wetter skimmate, less time to drain, outlet valve will need to be opened more.

    Because pin wheel pumps pull air and water... they are very sensitive to changes in depth. Get a air meter and see what one inch of depth does to air draw. It is significant. There is simply a range because people want to run it different. But the water level inside the chamber needs to be where the manufacturer says to put it... after that... lower it to run it for wetter skimmate, raise it for drier skimmate..... and if you do not have a choice, then the manufacturer is simply stating the acceptable water depth their skimmer will work in.
     
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  9. Powerman

    Powerman Giant Squid

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    that one has actually been quite debated by both sides. Wet and dry. Dry always goes on and on how dark their crap is and how totally nasty their coffee is. Big deal... just more concentrated, not more organics. For a long time it was held that wet "should" remove more... but in all actuallity, it probably removes the same. Holmes-Farley argued that less water draining "should" mean less organics lost and more removed.

    But after that sank it, I asked him about it... he said he never meant he actually has data to support it, but that it should. More than likely there is no difference. Meaning that wet skimmate drains less.... but if an organic is still bound in the skimmer... just not moved up to the cup, it is still "removed" from the system overall which is the point.

    After that, I still ran mine wetter... Looked like tea. Not for any scientific reason, but simply because it was easier to clean than when it was dry.
     
  10. m2434

    m2434 Giant Squid

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    All of the tests I've seen show less power consumption with lower water levels. For example, here:
    - REVIEW - SRO XP-2000 Cone Skimmer - Reef Central Online Community

    40scfh @ 25watts in 6" of water
    42scfh @ 27watts in 7" of water
    45scfh @ 28watts in 8" of water


    Although, it does pull more air at higher water levels. Physics was one of my favorite classes in college, but that was the last time I used any of it. So, I'll leave that debate for you guys. Nowadays, I just go by the numbers ;D
     
  11. salt4me

    salt4me Skunk Shrimp

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    My 50cents is this, no mater what depth water you put the pump in it runs the same. Now what matters is the head it pushes (colum of water). Pressure increases on the pump with the height it pushes the water up or it will also increase with each bend. As far as changing the effectiveness really cant see that.
     
  12. Dingo

    Dingo Giant Squid

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    Ohh man, this turned out to be a real interesting discussion! Lots of good info being thrown around here :)

    One question I have for this statement below is: if you have less water movement through your skimmer due to a lower water level is it reasonable to say that the slower movement will have more time for organics to be pulled out therefore making it slightly more efficient?