PVB question

Discussion in 'Irrigation' started by Dirt Boy, Aug 29, 2011.

  1. Kiril

    Kiril LawnSite Fanatic
    Messages: 18,334

    This is an issue of both pressure and time .... pressure drop downstream of the PVB and time required to fill the irrigation mains & laterals. Let's assume he is using a Febco PVB, which starts to dump when downstream pressure falls below 5 PSI (i.e. the air inlet poppet requires 5 PSI to seal properly) and will fully open at 1 PSI downstream pressure per specs. The goal here is to maintain downstream pressure above 5 PSI until the pump kicks in.

    In addition to a slow opening master valve (or as a possible alternative), another way you could potentially do this is to maintain a "leak proof" system by first making sure you aren't getting any low head drainage (i.e. use sprinklers and drip lines with check valves). The more water/pressure you can keep in the irrigation mains and laterals between irrigation events, the less water/pressure and time it will require to bring the downstream lines back up to operating pressure and flow.
  2. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,367

    this problem isn't solved until we nick the homeowner for an additional thousand dollars :)
  3. Dirt Boy

    Dirt Boy LawnSite Senior Member
    Messages: 489

    Don't mean to confuse you, there is a pump relay, but it is not turned on by the sprinkler controller. It is turned on by the pressure switch at the very small pressure tank.
    Thus, by the time that pressure switch "sees" low pressure and activates the pump, the main line pressure has dropped significantly and the PVB pops open.
  4. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,367

    what are the pressure switch settings?
  5. Dirt Boy

    Dirt Boy LawnSite Senior Member
    Messages: 489

    Not sure, it just has settings you can choose 40, 50, etc. right now it's at 60
  6. stebs

    stebs LawnSite Senior Member
    Messages: 498

    What if you had a very small zone such as a small drip zone or just a couple heads as the first station in the lineup? Just enough to slowly bleed down the pressure and get the pump running, but big enough to keep the pump running.
  7. Dirt Boy

    Dirt Boy LawnSite Senior Member
    Messages: 489

    Thought of that, basically doing what Kiril suggest, just different way:laugh:
  8. bcg

    bcg LawnSite Bronze Member
    from Tx
    Messages: 1,865

    You guys sure are devoting a lot of effort to fix a PVB that's working exactly as designed. As long as the PVB was installed correctly (somewhere that the dumping water isn't an issue), leave it alone. This reminds me of NASA spending millions of dollars to develop a pen that would work in zero gravity while the Russians chose to use a pencil. Sometimes the pencil is really the better solution.

    Messages: 18,668

    On a subject similar to this. How would a well on a pressure tank cause water hammers at startup and during zone changes? All the piping allows for 5fps. It cycles every 45 seconds if that means anything.
  10. AI Inc

    AI Inc LawnSite Fanatic
    Messages: 26,797

    Pete, if its cycling every 45 seconds , its not using enough water. Between the cycling and the water hammer I would guess that ya have bucu water and are not using all that much of it.

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