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Fluid through a pipe

  1. Oct 12, 2014 #1
    I have a pipe with regular diameter connected to a tap, the water comes from public supply, I assume that public supply can vary on pressure and flow rate. How can I guarantee that I allways get the same volumetric flow rate at the end of the pipe? Will a pressure reducer be sufficient?

    Thank you!
     
  2. jcsd
  3. Oct 17, 2014 #2
    Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
     
  4. Oct 19, 2014 #3
    Have you studied "Streamlined Flow" ?
     
  5. Oct 19, 2014 #4

    russ_watters

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    A pressure regulator followed by an orifice (or adjustable valve like a circuit setter) will do it.
     
  6. Nov 16, 2014 #5
    What is the purpose of the orifice? Can I apply Bernoulli's principle with the pressure reducer? In that case when pressure drops the velocity would have to increase, but that would mean that flow rate would increase aswell, which makes no sense. I'm really confused.
     
  7. Nov 16, 2014 #6

    russ_watters

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    No, you can't apply Bernoulli's equation to a pressure reducer. A pressure reducer causes the flow to lose energy.

    The reason for the orifice is to provide a significant and consistent pressure drop to help achieve the required flow. You may not need it if your piping system is long and small enough (to have its own significant pressure drop), but you didn't give any details of the system for us to really know.
     
  8. Nov 16, 2014 #7
    I got the first part.

    How can I relate the pressure drop with the flow rate then?
     
  9. Nov 16, 2014 #8

    russ_watters

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    For that part you probably do use Bernoulli's equation, as well as some other things like the loss coefficient of an orifice. I can't give you details though without having a better idea of what the system is going to look like.
     
  10. Nov 16, 2014 #9
    I just want to connect a pipe into a regular home tap and guaratee the same volumetric flow rate no matter the variations of pressure or velocity of the supply.
     
  11. Nov 16, 2014 #10

    russ_watters

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    A home tap? You mean a faucet or shower? The flow rate is going to vary with the changes in how open the faucet valve is (or how many are open). There really isn't any way to make that constant.
     
  12. Nov 16, 2014 #11
    Yea, a faucet. So even if I leave the faucet always open and use an electrovalve to open and close my system, wont be able to make a constant flow?
     
  13. Nov 16, 2014 #12
    What I really want is a way to make the electrovalve close after I have x liters of water passed through the pipe. If I had constant flow rate, I could set a timer on the electrovalve. Is there any other way to solve this?
     
  14. Nov 16, 2014 #13

    russ_watters

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    If you always open it 100%, yes, you could do this. An adjustable pressure regulator and an orifice or some long run of pipe will enable you to get a constant flow.
     
  15. Nov 17, 2014 #14
    What if multiple faucets are open, won't affect my system?
     
  16. Nov 17, 2014 #15

    sophiecentaur

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    A good low - tech solution could be to use a constant head arrangement. A water tank in the roof, with a standard ball-cock would achieve that and it would means a pretty constant flow out of the tap / faucet. Pressure regulators are a bit more complex (and probably more expensive too) than simple plumbing components.
     
  17. Nov 17, 2014 #16

    russ_watters

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    Yes, multiple faucets open will affect the flow.
     
  18. Nov 17, 2014 #17
    If constant volume delivery is all you want to achieve, why don't you just use a float value like in a toilet tank or carburator bowl. (Thank Sophiecentaur for suggesting the use of standard plumbing hardware). You can set the float value to give you the volume you want.

    Chet
     
  19. Nov 17, 2014 #18
    I see what you'r saying, I proposed that to my teacher, but he wants to avoid the use of a tank. Also, the volume of fluid that I will need to be delivered will vary often. With constant flow rate it would be a matter of just adjust the timers. Would a flowmeter be helpful?
     
  20. Nov 17, 2014 #19

    cjl

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    If you can't use some sort of a tank, a flowmeter is probably your best bet.
     
  21. Nov 17, 2014 #20

    sophiecentaur

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    It all depends on the actual values involved (pressure, flow rate even how long it will be operating for AND cost and accuracy required) can you afford an overflow ( waste)? That's the standard, instant constant head solution. Can you accept short term variations ? A small pump controlled by a flow rate meter could be very accurate but would that be necessary. I think he's being a Nazi, not to let you use a tank (haha). It would be my fave by far. What are his practical objections to it? (I assume that you don't need several Bar of pressure).
     
  22. Nov 18, 2014 #21
    It will be operating about 10-15min and not even everyday. The system will be a rack with 4 shelves and 24 mouse cages, the need is to deliver around 750ml on the pre-selected cages, that's why the volume will vary. It doesn't need to be super accurate, we want to fill the bottom of the cage with water, but we don't want to drown the rats lol. We tried a first approach with a tank on top of the rack, but then we came to the conclusion that it would be complex, and not very flexible, the rack will need to change places sometimes.
     
  23. Nov 18, 2014 #22
    If you were wanting to install a shower with a guaranteed flow rate, you'd get a "power shower" which is a shower with a built in pump and mixer valve. Any constrictions on the pipes would fail when the water pressure changed.

    If it were an aquarium or swimming pool water treatment system, you would need pumps and a time switch.
     
  24. Nov 20, 2014 #23
    From what I've read, Darcy Weisbach equation allows the calculation of fluid velocity related to pressure loss due to friction, but how can I calculate the effect of pressure drop on velocity of fluid on a pressure reducing valve? Is it just experimental?

    Thank you.
     
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