Need help calculating Friction loss for IRRIGATION

Discussion in 'Irrigation / Sprinkler Forum' started by DGM_Jakarta, Dec 3, 2008.

  1. DGM_Jakarta

    DGM_Jakarta New Member

    Messages:
    17
    Location:
    Indonesia
    Dear All, :confused:

    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 :confused:
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    What the heck are you irrigating with a 20" pipe...the moon???
    Let us know if you pass the exam you are taking!
  3. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,308
    Location:
    Yakima WA
    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.
  4. DGM_Jakarta

    DGM_Jakarta New Member

    Messages:
    17
    Location:
    Indonesia
    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. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,308
    Location:
    Yakima WA
    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.
  6. DGM_Jakarta

    DGM_Jakarta New Member

    Messages:
    17
    Location:
    Indonesia
    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???
  7. DGM_Jakarta

    DGM_Jakarta New Member

    Messages:
    17
    Location:
    Indonesia
    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??
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,277
    Location:
    Cave Creek, Arizona
    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.
  9. valveman

    valveman Moderator Staff Member

    Messages:
    4,382
    Location:
    Lubbock, Texas
    Send me a drawing of the layout with elevation changes, pipe size and class, and I can help you figure this out.
    Cary
  10. DGM_Jakarta

    DGM_Jakarta New Member

    Messages:
    17
    Location:
    Indonesia
    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. valveman

    valveman Moderator Staff Member

    Messages:
    4,382
    Location:
    Lubbock, Texas
    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.
  12. DGM_Jakarta

    DGM_Jakarta New Member

    Messages:
    17
    Location:
    Indonesia
    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. valveman

    valveman Moderator Staff Member

    Messages:
    4,382
    Location:
    Lubbock, Texas
    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.
  14. DGM_Jakarta

    DGM_Jakarta New Member

    Messages:
    17
    Location:
    Indonesia
    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. valveman

    valveman Moderator Staff Member

    Messages:
    4,382
    Location:
    Lubbock, Texas
    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.
  16. valveman

    valveman Moderator Staff Member

    Messages:
    4,382
    Location:
    Lubbock, Texas
    I would use a gate valve on the discharge of the pump. Start the pump with the gate valve closed or almost closed. Then slowly open the valve to fill the pipe line. If you just turn on the pump with no valve, or no water in the pipe line, the pump will not have any head against it. This will make the pump produce too much water, too much velocity for the pipe, and possibly even overload the motor. Once the pipe is full and flow is moving, you can open the gate valve all the way. The pipe is what puts the head on the pump. If you turn on the pump into an empty pipe line, there is not enough head, so the pump will produce too much flow and use too much horse power.

    A soft start on the motor WILL NOT be slow enough to get the pipe line full before the pump goes to full speed. A VFD cannot speed the motor up slowly enough to work. Even when the pipe is full of water, you need to start the pump against a closed valve, and slowly open the valve to prevent surge.
  17. Wet_Boots

    Wet_Boots Sprinkler Guy

    Messages:
    798
    Location:
    Metro NYC
    Hey Valveman, ever hear of using a ram pump for a project like this? (who, if anyone makes one this size, I wouldn't know)
  18. DGM_Jakarta

    DGM_Jakarta New Member

    Messages:
    17
    Location:
    Indonesia
    Cavitation

    Mr Valveman, i already held a meeting about this, they still calculating again, then again i still have some question, please do not be bored with my question. :). How about the cavitation in the pipe and valve, is there any risk. by the way i love this forum, we can change ideas and solve the problem. This is kind of forum that we really need. :cool:
    back to the question, how do you get the information, is there any calculation to show me and how to calculate? :D

    Anyway your suggestion that i dont need bigger pump with bigger power to achieve that pipe length, from your information the pump power will not exceeded 200 Hp. we think of changing the pvc pipe 20" to pvc pipe 16". Because the total sum of $$$ we still trying to calculate how much $$$ we have to spend.
  19. valveman

    valveman Moderator Staff Member

    Messages:
    4,382
    Location:
    Lubbock, Texas
    I would not try to push more than 4,000 GPM through a 16" pipe. If the velocity is higher than 7 FPS, the pipe will come apart. I am using the friction loss chart in an old Hunter Irrigation book that I have had for many years. You can also find friction loss charts on the Internet, check with your pipe manufacturer.

    Cavitation is only a concern on the suction side of the pump. As long as your NPSHA is higher than your NPSHR, cavitation is not a problem.

    Starting and stopping the pump without causing water hammer or surge is the main problem. I would only start and stop the pump against a closed or almost closed valve.
  20. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    Should something this large have something similar to an air admittance valve at or near the pump for when the pump is stopped to compensate for possible negative pressure...I no nothing about systems this large...just a thought...
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