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Thread: PVC Pipe Flow Rates

  1. #1
    Dave's Avatar
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    PVC Pipe Flow Rates

    Hi all,

    Could some one please help me out with the flow rates, under Gravity, on the various
    sizes of PVC pipe please.

    Pump will be at the end so all flow thorugh pipes is under gravity. Pump capacity is 18k litres p/h at 0 head. (pedrollo)

    50mm (2")
    60mm (?)
    75mm (3")
    110mm(4")

    Thanks .
    Dave.

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  2. #2
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    The gravity flow through a pipe is greatly dependant upon the amount of water above the pipe opening.

    steve

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    Also on the length and slope of the pipe which affect velocities. Are you sure you're talking gravity flow? If the pump is directly on the end of this pipe, it's not gravity flow. Gravity flow is for examply, from the pond inlet, into an open top tank/barrel.
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    hi,

    to clarify, these pipes would be emptying into a chamber, and the pump would be in this chamber.
    So no, the pump is not directly attached.

    Thanks
    Dave.

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    For gravity flow, the flow rate through a given pipe will depend upon the "draw down" in the chamber. As you increase the water being pulled out of the chamber by the pump, the level in the chamber goes down. As it does, this increases the difference between the water level in the pond and the water level in the chamber, which increases the velocity through the connecting pipe. At some point, the draw down in the chamber impacts the function of the chamber - for instance, a settling tank is only half full and not "settling" due to a lower volume of water.

    Check out the following plumbing primer for lots of information on plumbing, draw down, and pipe capacities: http://www.koiphen.com/members/harve...umbing-2-1.pdf

    I'd suggest giving us some information on what you're trying to attain. 4" or 3" pipes are generally used for bottom drains, and usually 2" pipes for intra-pipe connections and TPR returns. This generally utilizes acceptable draw downs within the filter.

    Hope that helps.



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  6. #6
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    Ok,

    I am in the process of putting together a portable pond, i don't own my property.
    I am doing the pre planning at this stage. My PVC liner is already made. 5m x 2.8m x 1.15m (17x9x4; 4200usg)
    It will be around 16000l. I am in the process of designing the frame work to put the liner into.

    I will be going individual filter units (blue 220l) barrels coupled by pipes
    so two bd's to settlement. i like two cause i like redundancy on bd's (i once had to clear a bd at 1am in July at 10deg c water without a wetsuit)
    The BD's will be in the over the side retro fit style.

    The settlement will then be connected to three other Barrels in a top to bottom fashion.
    The pumps will be situated in the last chamber.
    I am going to be using a Resun PC-18000 which puts out 18k litres per hour at 0 head.
    i will use another pump at 4k l per hour to supply the UV light.

    So that is why i am concerned about the pipe sizing.
    will 75mm be ok for the bd's? and should i connect the barrels with 110mm or 75mm.
    Dave.

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    18000 l/hr is about 4000 gal/hr roughly. To gravity flow that with a one inch drop between tanks you will need a 4" pipe or two three inch pipes for that circuit. Your draw down will be slightly more than an inch but it will work. Keep the piping as short as possible and don't use any 90 deg fittings. How are you planning on laying the system out. How are the two circuits going to run. Two drains on seperate circuits combined at all?
    Depending on pipe lengths and bends In general a 2" line will gravity flow approx 900 gph at a one inch drop. A three inch line will flow about 1800 gph and a 4 inch line will flow about 3600 gph.

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    Thank you for that reply Kent.

    The BD will flow in at the bottom of the first drum.
    It will be a up and over the side, so will drop 90cm 35" to the bottom of the settlement.
    From the settlement it will overflow from the top of the SC to the bottom of the next barrell, this pipe drop will be 30".
    and so forth from 2 to 3 and from 3 to 4.

    Everything is levelled on pond water level.

    Now i assume i cant just take the above figures given for a 1" drop and multiply it by 30?
    Dave.

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    Quote Originally Posted by Dave View Post
    Thank you for that reply Kent.

    The BD will flow in at the bottom of the first drum.
    It will be a up and over the side, so will drop 90cm 35" to the bottom of the settlement.
    From the settlement it will overflow from the top of the SC to the bottom of the next barrell, this pipe drop will be 30".
    and so forth from 2 to 3 and from 3 to 4.

    Everything is levelled on pond water level.

    Now i assume i cant just take the above figures given for a 1" drop and multiply it by 30?
    All of the drop calculations are from the top of one container to the top of the other container - doesn't matter how deep the outlet is. I presume there isn't a 30" drop between the level of pond water and the top of the water in the settlement tank? If your pump is off, the level in the two bodies of water (pond and settlement) would be the same. When you turn the pump on, the top of the water in the settlement tank will drop to 1" below pond level if you're flowing at a rate that is "1" draw down" in the charts.

    How do those "up and over" retro BDs work? I've never been clear on how to get the water to go up the pipe, above pond level, and then back down to the settlement tank. Seems like the top of the bend would slowly fill with air entrained in the water and flow would stop.



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  10. #10
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    When they are flowing they work very well. seeing as the pipe work is glued, and the inlet and out let are under water, no air gets in. They work the same way as an overflow system works on a fish tank.
    The only real problem is getting them going, which is basically a matter of getting the weight of water on one side and a little sucking work on the other side.
    had more than one lung full of water.

    Here are two pics of a 50mm overflow on a 4ft tank, it works the same on a pond. only difference is that the end is attached to the settlement/vortex.



    Last edited by Dave; 03-18-2011 at 04:43 AM.
    Dave.

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    Hey you know what I did on my siphon tubes on my marine fish tank? No of course you dont but Im going to tell you.. I used a power head attached to air lines, these air lines went to the top of the siphon tube, when the siphon had air or needed to be primed The venturi from the powerhead would pull in air and aerate the water. Then as it pulls the air out of the siphon it will pull up the water until it starts flow over the wall. When its full the powerhead just sucks water through the line and the bubbles stop and it just waits until air starts to accumulate (and it will) then it removes it on the fly keeping your siphon primed all the time without getting your lungs full of water. Then you can use your lungs for breathing instead.
    gOOse.

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    Thanks gOOse, thats an awesome idea.
    Dave.

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    Cool glad it helped.

    gOOse.

  15. #15
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    Ok,
    Wasn't concentrating.
    I get the draw down.

    blond moment.
    Dave.

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    "There is nothing wrong with making mistakes. Just don't respond with encores"

    _____________________________________________

    I asked Jesus how much do you love me? Jesus replied this much and he stretched his arms on the cross and died...
    _____________________________________________


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