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Thread: Need help calculating Friction loss for IRRIGATION

  1. #1
    DIY Junior Member DGM_Jakarta's Avatar
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    Exclamation Need help calculating Friction loss for IRRIGATION

    Dear All,

    I have a roject for Irrigation that need calculation of friction loss, I tried the freecall but not sure if its correct. The problem are for case 1 & 2
    1. Diameter of the pipe : 20"
    Material of pipe : PVC
    Length of pipe : 1600 Metre Horizontal
    Elevation : 5 Metre
    Flow rate that i use : 300 Litre/second
    Pressure at : 1,5 Bar
    After that i used reducer and add another Pump for :
    Diameter of the pipe : 16"
    Material of pipe : PVC
    Length of pipe : 1035 Metre Horizontal
    Elevation : 1 Metre
    Flow rate that i use : 150 Litre/second
    Pressure at : 4 Bar
    Can anyone help me count the friction loss pleaseeeeeeeee, i need urgently

    2. Diameter of the pipe : 20"
    Material of pipe : PVC
    Length of pipe : 2100 Metre Horizontal
    Elevation : 5 Metre
    Flow rate that i use : 300 Litre/second
    Pressure at : 1,5 Bar
    After that i used reducer and add another Pump for :
    Diameter of the pipe : 16"
    Material of pipe : PVC
    Length of pipe : 1740 Metre Horizontal
    Elevation : 0 Metre
    Flow rate that i use : 150 Litre/second
    Pressure at : 4 Bar
    Can anyone help me count the friction loss pleaseeeeeeeee, i need urgently

    and how much losses at PVC Tee 20", PVC Elbow 20", Gate Valve cast iron 20".
    Thank you very much... please... please.... somebody... helppppp

  2. #2
    Plumber jimbo's Avatar
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    What the heck are you irrigating with a 20" pipe...the moon???
    Let us know if you pass the exam you are taking!

  3. #3
    In the Trades Gary Swart's Avatar
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    Whatever this project is, it is beyond home plumbing or even a commercial building plumbing. You need to hire an engineer that can deal with something the size of what you are doing. There has to be many technical aspects to deal with and not only require expertise in the field, but on-site evaluation. I'm sure many of us would love to be able to give you the assistance you need, but you need more than even the expert plumbers here can supply. Yours is not a do it yourself job to say the very least.

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    DIY Junior Member DGM_Jakarta's Avatar
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    Hahahaa, Dear Gery im not try to water the moon, actually it is a project irrigation for planting the rice. the area that need to be watered are length 2,7 Km straigh and 1,7 Km down, and 2,2 Km right after down. I need a pump or a system to push water that far, the consultant required 20" PVC pipe so the friction loss can be minimize, and my job is to calculate the friction loss and design the system so the water output can be 150 Liter/second. Any suggestion bro?

  5. #5
    In the Trades Gary Swart's Avatar
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    My point is simply that this job is not a "plumbing" job nor is it a typical lawn sprinkler installation. This is a very large project that requires on-site engineers. While you are welcome on this forum, this is a Do It Yourself site and certainly this particular project is beyond DIY and even if a reader has the qualifications to deal with your problem, there is no way he could or would be able to help much by just answering a few questions, especially for free. Hire an engineering company to design this job. Otherwise, you are headed for disaster.

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    DIY Junior Member DGM_Jakarta's Avatar
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    Smile You right

    Well i got the point there Gery, i know this is a larger scale, and also this is my first project i never design or calculate at this much. very well then heads up and looking for some experts engineering for this matter. Any suggestion of the firm???

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    DIY Junior Member DGM_Jakarta's Avatar
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    Exclamation Correction to metrics

    very well then but how can i choose the right pump if they want to use pvc pipe with total length of 14107 feet, the capacity what im asking are 4755 USGPM and i still cannot calculate how much psi that i need to fill the pipe till end of pipe. The rivers depth are around 23 feet to 33 feet. The problem is how to design the pump and how many pump i have to use along the pvc pipe, but please consider that the maximum pressure for pvc pipe are 116 psi. Thanks guys, any suggestion??

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    Moderator & Master Plumber hj's Avatar
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    Default pump

    THAT is the reason for an engineer. Just pushing the water through the pipe creates back pressure. The pump has to be able to deliver that volume against the developed head pressure, and if the volume is increased so will the head pressure. At some point, called the maximum, it will be impossible to increase the flow because doing so will create more head pressure than the pump can develop. Finding that maximum and staying below it with your pipe size and length is why you need an engineer. It may be that your pipe size could be inadequate when all the numbers are put together.

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    Moderator valveman's Avatar
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    Send me a drawing of the layout with elevation changes, pipe size and class, and I can help you figure this out.
    Cary

  10. #10
    DIY Junior Member DGM_Jakarta's Avatar
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    Default More information

    Thanks guys, maybe i can clear it like this :

    Pipe length are 14107 feet with diameter 16" or 20" pipe material is PVC with maximum pressure allowed 116 PSI, the capacity what im asking are 4755 USGPM and total Head = ???
    along the pipe there are 3 gate valve to water the plant.
    The elevation ground are about 17 feet from the pump to the end of pipe. The length of suction pipe are 22 feet from the pump. and the question are how you calculate how much pressure the pump need, is it possible if i place 2 or 3 pumps along the pipe to boost the water with this design maybe i can lowered the pressure. Can the design work? the main pump i use a horizontal split casing pump (Flow rate: 4755 USGPM, pressure 21.8 PSI), material cast iron, impeller bronze, standard.
    the booster pump i use the centrifugal end suction pump (Flow rate: 2.38 USGPM Pressure 58 PSI). Thanks.

  11. #11
    Moderator valveman's Avatar
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    The class of the pipe will still make a difference. I will use class 235 for a worst case scenario. With 16" pipe going 14107' at 4800 GPM, you loose .46 PSI per 100'. That would be 65 PSI plus the lift of 17' which is another 7 PSI. 72 PSI is a total head on the pump of 166'. So your pump would need to deliver 4755 GPM at 166' of head, not counting any suction lift.

    With 20" pipe, the pump only needs to deliver 4755 GPM at 68' of lift. This will take a pump with a little over 80 HP for 20" pipe, and a little less than 200 HP for 16" pipe. As always, the best way to save energy is to use larger pipe.

    A single pump will do, as even with the 16" pipe, the max pressure on the pipe line will be about 72 PSI. The velocity in 16" pipe will be 8.19 FPS, and with 20" pipe would be 5.31 FPS. You are going to need to use the 20" pipe.

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    DIY Junior Member DGM_Jakarta's Avatar
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    Thumbs up Dear Valveman, Thankk youuu

    Yooo Valveman, thanks a lot you are the first person with reasonable idea, i knew that the consultant engineer in here is wrong. I also think we dont need more pump, but are you already minus it with the friction loss between the valve, the pump and the pipe, im a little bit consern about this, should we add more psi to the number you gave me? then again thank you so much brother...

  13. #13
    Moderator valveman's Avatar
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    A standard 20" tee is like adding another 25' of pipe. A standard 20" elbow is like adding 50' of pipe. And a 20" gate valve is like adding 12' of pipe. Then the friction loss and head for the pump figured will not give you any pressure at the end of the line. If you are just dumping into an open tank, this should be all the head you need. If you need pressure at the end of the line, you will need to add the additional pressure required.

    Maybe I don't understand your last question. If your pump delivers more head than you need, then it will produce more flow than you want.

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    DIY Junior Member DGM_Jakarta's Avatar
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    Thumbs up Wow, one more time Wow

    Thanks Valveman for such a quick reply, I dont need more pressure at the end of the line, because it is for rice farm, the water just coming up with no pressure at all to dewatering the farm. anyway im gonna held a meeting to study your opinion and hopefully the consultant will change their statement and calculate again with your theory. oh yeah one more thing should i add one pressure tank about 528 USGPM to maintain the pressure and the flow in the pipe. Or may i use the Pressure reducing valve and put it after the tank. Thanks againnn and you are the greatest.

  15. #15
    Moderator valveman's Avatar
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    I don't see why you would need a pressure tank. The pump will maintain pressure and flow in the pipe line. If you size the pump correctly, you won't need a pressure reducing valve. A PRV would only be needed to reduce flow and pressure if you oversize the pump.

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