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Thread: new terrarium project

  1. #9
    stretch.... yawn... jbradt's Avatar
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    Good to know. Thanks dude!
    Indeed. Most indeededly. Phillip J. Frye


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    Av8tor1's Avatar
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    little more in depth pump and valve theory..... I know, I know... too much information LOL

    Its better to have a smaller pump then a large pump that is being restricted a lot.... ideal would be no more then a 10% reduction in flow. What happens is as you restrict the flow of a centrifugal pump the relative speed of impeller to fluid becomes excessive. (image you driving along side a train at the same speed compared to the train rushing by you as you bearly move)

    This increase in relative velocity causes a low pressure area to form on the impeller blade tips (Bernoulli's principle).... and this results in a condition called cavitation. Cavitation will eventually cause erosion of the impelller blade tips. (In our application, I wouldnt worry about blade tip erosion LOL)

    (This is how we (USA) use to track USSR submarines, their ship's screws had a tendency to cavitate)

    A partially open ball valve or gate valve causes the same condition. This is why you will sometimes hear an outside water spigot (these are gate valves) "sing". That singing noise you hear is when the valve is partially open is cavitation. Whereas your faucets inside the house are not gate nor ball valves and do not suffer from this condition. (They are what is known as globe valves)

    there will be a test Monday,

  3. #11
    stretch.... yawn... jbradt's Avatar
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    Quote Originally Posted by Av8tor1 View Post
    little more in depth pump and valve theory..... I know, I know... too much information LOL

    Its better to have a smaller pump then a large pump that is being restricted a lot.... ideal would be no less then a 10% reduction in flow. What happens is as you restrict the flow of a centrifugal pump the relative speed of impeller to fluid becomes excessive. (image you driving along side a train at the same speed compared to the train rushing by you as you bearly move)

    This increase in relative velocity causes a low pressure area to form on the impeller blade tips.... and this results in a condition called cavitation. Cavitation will eventually cause erosion of the impelller blade tips.

    (This is how we (USA) use to track USSR submarines)

    A partially open ball valve or gate valve causes the same condition. This is why you will sometimes hear an outside water spigot (these are gate valves) That singing noise you hear is when the valve is partially open is cavitation. Whereas your faucets inside the house are not gate or ball valves and do not suffer from this condition. (They are what is known as globe valves)

    there will be a test Monday,
    So, how does using the adjustment built into the pump play into this? Since I'm using the pump at nearly it's lowest setting, does that count as restricting the pump? Or does this more refer to external valves/restrictions?
    Indeed. Most indeededly. Phillip J. Frye


    My growlist.

  4. #12
    Av8tor1's Avatar
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    Jb, i wouldnt worry about it.....

    Sometimes i go off the deep end... my main point is bigger is not always better. Some of us would instinctively think buying a big pump and just restricting it would be wise...

    Our application is intermittent use and with a pump that is relatively inexpensive... we dont need to get 1,000's of hours of operation

    For the ones that will follow you with this thread, dont buy the biggest pump you can find and choke it down. In addition to cavitation concerns, that flow is also what cools and lubricates the pump.



  5. #13
    stretch.... yawn... jbradt's Avatar
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    Quote Originally Posted by Av8tor1 View Post
    Jb, i wouldnt worry about it.....

    sometimes i go off the deep end... my main point is bigger is not always better. Some of us would instinctively think buying a big pump and restricting would be best when it isnt...

    Our application is intermittent use and an pump that is relatively inexpensive... we dont need to get 1,000's of hours of operation

    For the ones that will follow you with this thread, dont buy the biggest pump you can find and choke it down



    Gotcha. For the record, I bought the smallest one I could find. LOL
    Indeed. Most indeededly. Phillip J. Frye


    My growlist.

  6. #14
    richjam1986's Avatar
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    It'll be great to see how it ends up working. Cp's definately enjoy water flow and keeping the water fresh
    Da' mishu
    Provo, Utah.

    My Growlist: http://www.terraforums.com/forums/sh...29#post1089429

  7. #15
    stretch.... yawn... jbradt's Avatar
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    Thanks, Rich!

    After a bunch of tests, I've noticed that every now and again when the pump turns on it doesn't seem to be able to push the water up the tube. Turning it off then on again clears up the problem. I figure it must be pressure left in the tube from the draining. Anyone have any thoughts as to what's going on or how to solve the problem?

    Anyway... I've found some glass to cut a top from. Still working on plans for keeping the ambient humidity up. Hopefully Saturday I'll be able to get back into it and make some more progress.
    Indeed. Most indeededly. Phillip J. Frye


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  8. #16
    Av8tor1's Avatar
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    Mine does that if I place it in the reservoir with the inlet to the bottom. I have to assume it's just a lack of starting torque. It's never done it in any other position.

    Try laying the pump on one side or another and see if that helps. It may be just enough of a diference in loading to cure the problem. The problem may also fix itself as the rotor bushings loosen up a little with use.

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