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Adjusted Static Pressure

Discussion in 'Irrigation' started by PurpHaze, Oct 7, 2006.

  1. PurpHaze

    PurpHaze LawnSite Fanatic
    Posts: 5,496

    Was doing some reading in my Turf Irrigation Manual (Watkins) looking for a formula and came across a section I'd hi-lited many years ago pertaining to designing systems with the anticipation of decreased pressure occurring in the future. Considering all the recent discussion on systems that have developed similar problems I thought I'd share a few passages for those that don't have this valuable resource book.

    "Gauged pressures in excess of 60 PSI should be especially suspect. Water distribution systems are designed in new neighborhoods to allow for building, extension of mains into even newer areas, and reduction of main capacity due to deterioration from aging. Thus, immediate pressure in a new neighborhood is usually substantially greater than the future low pressure.

    As a general rule, systems should be designed to operate on less pressure than the anticipated low pressure in new neighborhoods and known low pressure in older ones. This protects the system from anticipated pressure drops.

    When low static pressure is: Allow: Design for:
    50 PSI 10% 45 PSI
    75 PSI 15% 65 PSI
    100 PSI 20% 80 PSI
    125 PSI 25% 95 PSI

    A further argument in support of conservatism is the necessity to design systems to function properly on hot days when pressure will be lowest. This is obviously the time when good, dependable, artificial watering is needed most."

    Interpretation: Plan ahead!!! :)
  2. Dirty Water

    Dirty Water LawnSite Fanatic
    Posts: 6,799

    We usually pressure regulate down to 50 psi on any extreme pressure situtations.

    Saves too, when the pressure goes away. I ran into a home with 150 psi on the main. New development, I bet it will drop when all the houses are built.

    Good post :)
  3. PurpHaze

    PurpHaze LawnSite Fanatic
    Posts: 5,496

    Thanks. Maybe I'll post it in the sticky thread too.

    A good designer will prepare for the future. A shoddy one will say, "Heck, when the pressure drops and their system no longer works then we'll get more money out of them on a redesign." :dizzy:
  4. PurpHaze

    PurpHaze LawnSite Fanatic
    Posts: 5,496

    Interesting, Jon. From the Sequim city web site. :)

    "How do I find out what my water pressure is?"

    "Call Public Works Department with your address and we will provide you with the water pressure or assist you in getting your water pressure for you."
  5. Dirty Water

    Dirty Water LawnSite Fanatic
    Posts: 6,799

    Bah, They could just say 45 psi and it would be accurate 95% of the time Heh.
  6. YardPro

    YardPro LawnSite Gold Member
    Posts: 3,563

    we always leave a 25% reservve on flow and pressure.

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