gpm???

Discussion in 'Irrigation' started by offshore1234, Jul 10, 2008.

  1. offshore1234

    offshore1234 LawnSite Member
    Posts: 17

    Ok, I was told to check the gpm by cutting into my main line (1 inch) just ahead of the water meter and filling a 5 gallon bucket out of the 1 inch pipe. I put a "T" in the line and ran a piece of 1 inch pipe down off that with a 1 inch stop valve to check the flow. I filled up a five gallon bucket in 8 seconds. By the math 5 gal/60 x 8= 37.5 gpm. This seems like alot. I was told that the max safe flow is around 18 gpm. What does this mean? Do I need to get my gpm down to 18gpm, and if so, how? I was going to run the system with 1 inch poly and 3/4 inch laterals. Any help would be appreciated. Also, my pressure is 58 psi.
     
  2. lowvolumejeff

    lowvolumejeff LawnSite Member
    Posts: 72

    Welcome! Hey, did you mean AFTER the meter? Makes a difference, since meters eat pressure. Anyway, you sound as if you need some help, and also want to understand how it works. Jess Stryker has a free on-line tutorial site that will help out. Spend a little time there and you won't be sorry. http://www.irrigationtutorials.com/

    Jeff
     
  3. lowvolumejeff

    lowvolumejeff LawnSite Member
    Posts: 72

    Before I get slammed, I do understand that static pressure is the same on either side of the meter. Jeff
     
  4. Waterit

    Waterit LawnSite Silver Member
    Posts: 2,888

    37.5GPM open discharge = 18GPM +/- usable - right on the money.

    Where/how did you measure pressure?
     
  5. offshore1234

    offshore1234 LawnSite Member
    Posts: 17

    I am not sure I understand. How does 37.5 open discharge = 18 gpm usable. Please explain.
     
  6. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,020

    If you cut in just downstream of the meter, and tee off and come up to a shutoff valve that has a pressure gauge on its upstream side (you can swipe the valve from a backflow preventer) you can repeat the bucket test at different pressures.
     
  7. offshore1234

    offshore1234 LawnSite Member
    Posts: 17

    Why would I want to redo the test? Are the numbers that I am coming up with ok or does something need to be done. Also, does anyone know what waterit means when he says: 37.5GPM open discharge = 18GPM +/- usable - right on the money.

    Thank You
     
  8. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,020

    Are you going to have a POC just downstream of the meter? If so, that's where you cut in to do the test. And with a gauge upstream of your added shutoff valve, you can flow enough water to get a certain pressure reading, say 50 psi, and see what the flow is. Now you have a precise number to work with, and no guesstimating required.
     
  9. offshore1234

    offshore1234 LawnSite Member
    Posts: 17

    Yes, but can I use the readings I have. The flow was 37.5 gpm at 58 psi.
     
  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 47,020

    Then what's the static (no-flow) pressure?
     

Share This Page