Water velocity/damage

Discussion in 'Irrigation' started by Dirt Boy, Feb 11, 2008.

  1. Dirt Boy

    Dirt Boy LawnSite Senior Member
    Messages: 489

    Just wondering about valve size/water velocity, etc.
    A typical 1' valve is rated for like 35 gpm, yet you shouldn't be designing for flows over 5fps. What is the logic behind this? just to make them stronger?

    What kind of damage occurs with an improperly designed system i.e. high velocity? Pictures of this, etc.

  2. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,367

    A lot of designs (older, maybe) go way beyond normal velocity recommendations. A one inch water meter has a 50 gpm rating.
  3. DanaMac

    DanaMac LawnSite Fanatic
    Messages: 13,209

    One thing your (this one's for Boots) trying to prevent is water hammer. Which can cause fittings to blow apart, noise within the pipes, early failure of valves. And if you have a fast closing valve like a RB DV, it can cause manifolds to blow up. I've repaired them due to it. But had to put in slower closing valves. Zones were way over capacity.
  4. Mike Leary

    Mike Leary LawnSite Fanatic
    Messages: 23,148

    Ditto..just what I was going to post.
  5. Dirt Boy

    Dirt Boy LawnSite Senior Member
    Messages: 489

    So, if you have an 1-1/2" supply, which can handle 30gpm (velocity wise), would you put a 1" valve (which is rated for 35gpm) in, or do you keep everything same size?

    Thanks again!
  6. DanaMac

    DanaMac LawnSite Fanatic
    Messages: 13,209

    To do it properly, you need to do a bunch of calculations and need to know more specs as well. Total GPM per zone, static pressure, meter size, supply line size, main line size, main line and lateral material, size of backflow preventer and what type. I'm not the best person to correctly describe how to do this. Maybe someone else can help. But it's more than just putting a 1" valve in just because it says the valve can handle x amount of GPM.
  7. Dirty Water

    Dirty Water LawnSite Fanatic
    Messages: 6,794

    One advantage of the extra flow rate of valves is that you can run a 1" valve with 1.25" pipe without an issue.

    It gets even better when you go up to 2" valves.

    A 2" valve can handle flow upwards of 100 gpm, so I have often used 2" valves with 3 and 4 inch mainlines.

    Huge savings in money that way :)
  8. Kiril

    Kiril LawnSite Fanatic
    Messages: 18,334

    Plus you can run multiple zones at the same time. :)
  9. JeffY

    JeffY LawnSite Senior Member
    Messages: 324

    Same here. We install the 2" valve on the 3" mainline and bump it back up to a 3" or 2 1/2" lateral supply depending on number of heads and balancing the pressures on the laterals.. Saves us tons of money.
  10. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,367

    You have to also look at pressure losses. Most one inch valves get lossy above 25 gpm. A one inch PVB, on the other hand, will work at 50 gpm (rated identical to the water meters) and more. Valve location also figures into water hammer effects. Excess flow on a system connected to house plumbing can have the entire home reverberate with water hammer. Put 'em by the street, and the same flow won't disturb anyone.

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