pump keeps loosing its prime

Discussion in 'Irrigation' started by zliminator, Jul 4, 2006.

  1. zliminator

    zliminator LawnSite Member
    Posts: 82

    I have a 1 HP pump on a 30' well with a foot valve on a 1-1/4" intake and a 1" discharge. After the pump shuts off I can hear water running through the pump and I have to prime it again. Do I need a check valve at the discharge?

    Dan
     
  2. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,014

    Are you pumping any sand? With clean water, the suction line check(s) should hold water and maintain prime. Certain pumps are much better at holding prime than others.
     
  3. zliminator

    zliminator LawnSite Member
    Posts: 82

    It looks a little brown when it starts up. I hope its not pumping sand.

    Dan
     
  4. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,014

    One thing to try is to add a master valve and small pressure tank to the pump, and to wire the pump through the pressure control switch. What this does is to set up a small area of positive water pressure, which makes it much easier to maintain pump prime.

    But first, make sure the suction line is sound. You might run the thing through a strainer to see what particles, if any are being pumped out. There can be a worst case scenario where sand gums up a foot valve, and a second suction-line check valve gets added at the pump inlet, and to protect it from fouling, a suction line strainer is installed. The strainer-check-valve combo can be placed at the output side of the pump, but that allows any leaks on the pump itself (like the shaft seal) to kill the prime.
     
  5. Like wet_boots stated check for a bad foot-valve or leak in intake line, no need for check on discharge.
     
  6. zliminator

    zliminator LawnSite Member
    Posts: 82

    I don't have the pump and valves tied into the timer yet. I have to open the valve manually and then go turn the pump on. When I shut the pump off and run over to turn off the valve then air gets back into the lines. Could that be why its loosing its prime?

    Dan
     
  7. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,014

    Is the suction line holding water? Is all the air out of the pump? This can take awhile to clear. Is it possible to connect the suction directly to the well point pipe? (assuming that's what you have)
     
  8. speedbump

    speedbump LawnSite Member
    Posts: 117

    You may have a split in your droppipe since nobody uses galvanized anymore. And the footvalve may be stuck open or missing. Pull the droppipe and check it out.

    The check valve up top is a bad idea.

    If you can avoid pulling straight off the casing in any way shape or form; do so. Doing this would mean a check valve up top and that is another easy to lose your prime.

    bob...
     
  9. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Posts: 48,014

    Since they manufacture 1 1/4 inch well points, and since many pumps have 1 1/4 inch suction connections, a direct pump/point connection is normal. For those, you do have a check valve right at the inlet of the pump, and the well point screen keeps particles from fouling the check. Also, the direct connection prevents the entry of air into the suction line while pumping. (like, when switching zones) And, if the well point screen gets clogged, it will, if a tee is on the suction line, be possible to force water back down the point improve the flow.

    Since we can't see all the details at the site, we can only give general advice. Not every shallow well with a 2 inch pipe is a well point. There are shallow well installations that use water pressure to blow sand away as the pipe is forced into the ground.
     
  10. speedbump

    speedbump LawnSite Member
    Posts: 117

    The biggest reason for lost prime with a check valve at the pump is an air leak between the check valve and the screen. The water is being held up in the well by a vacuum held by that check valve. If there is even the slightest air leak, the water is going to seek it's level in the well again and the pipe is not full of air. The first thing the pump sees when it starts up, is a big shot of air, not water.

    It's really hard to beat a well point into the ground without creating an air leak at the joints.

    bob...
     

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