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Measuring Dynamic Pressure at the Spray Head

Discussion in 'Irrigation' started by anotherbrian, Jun 9, 2011.

  1. anotherbrian

    anotherbrian LawnSite Member
    Messages: 21

    How do you measure dynamic pressure at the spray head?

    I have a PVC T connector with a pressure meter hung off the T.

    I can place it in line with the sprayer:

    || <-- supply

    Thus, this allows the sprayer to function. The measurement is made while the sprayer is

    Alternately, I can plug the end of connector and use it to replace the sprayer.

    || <--supply

    Which of these measurements would be considered the dynamic pressure at the head?

    Is that the measurement that would correspond to the pressure listed in the performance specs of the sprayer (e.g., Number 12 full sprayer shows 9 foot radius at 15 psi, 10 feet at 20 psi, 11 feet at 25 psi, and 12 feet at 30 psi).
  2. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,218

    the first, but I always shake my head at these measurings, because systems should never be designed so that you ever need these measurements
  3. Mike Leary

    Mike Leary LawnSite Fanatic
    Messages: 23,087

    When I was starting out, I bought a kit with a gauge and adapters for RB & Toro heads. It even included a pitot adapter for impacts. All I learned was the dead plants and the turf stressing were caused by a piss-poor design. I threw away the kit years ago.
  4. hoskm01

    hoskm01 LawnSite Fanatic
    Messages: 5,690

    Static=pressurized, no flow.
  5. Inspired

    Inspired LawnSite Senior Member
    Messages: 544

    It should look like my avatar
  6. anotherbrian

    anotherbrian LawnSite Member
    Messages: 21


    Mine too - piss poor design. I am making a study of it before making changes. I haven't worked out the calculations yet as to pressure losses based on pipes and valves, but I should have that done by tomorrow.

    Because I am on city water, I can measure my flow rate. And now I can measure the pressure at the spray head.

    I measure 22 gpm going into a zone which has 6 half sprayers (number 12H) and 5 full sprayers (number 12H). Assuming all that water makes it to those sprayers, that works out, on average, to be 2.8 gpm for the fulls and 1.4 gpm for the halves.

    But I measure only 17 psi at the spray head (and they all shoot out rather poorly). According to the # 12 product literature, a 20 psi (which I am not obtaining) uses 2.1 gpm for the full and 1.05 for the half. So working out the calculation, of the 22 gpm going through the city's meter, I am missing at least 5.75 gallons. Where did it go?

    I am suspecting that all that missing water is leaking out of the hydro index valve into other zones and dribbling out their spray heads.
  7. Mike Leary

    Mike Leary LawnSite Fanatic
    Messages: 23,087

    You don't need a gauge to tell a client they're screwed.
  8. mitchgo

    mitchgo LawnSite Silver Member
    Messages: 2,921

    shut off all the heads and start looking for a break

    Messages: 18,668

    Seen that happen. Get rid of the hydro indexing valve whether its the problem or not. Will make your troubleshooting a whole lot easier.
  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,218

    a traitor to your user name.... :p

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