Flojet demand pump - Always has air in lines, won't shut off right

Discussion in 'Pumps and Tanks Well Forum & Blog' started by cursethebanksters, Oct 2, 2012.

  1. cursethebanksters

    cursethebanksters New Member

    Messages:
    9
    Location:
    Arkansas
    Hello,

    I have a Flojet demand pump model 0356 144a in my travel trailer. I have had it a couple months and it just doesn't work right. Here is a link to it:

    http://www.amazon.com/Flojet-03526-144A-Diaphragm-Automatic/dp/B002P33KVQ


    First, I have to manually turn it on and off with a switch because it usually doesn't shut off like it's supposed to. I think because it still has air in the lines. Sometimes it does shut off though.

    Second, it seems to lose it's prime in between uses and gets air into the lines which has to be blown out every time I turn it on. I'm pretty sure it has a check valve built in.

    The inlet line runs from a storage tank that has a 3/4" pvc which adapts to 3/4" poly which then goes into a garden valve hooked up to 3/4" pvc, which then runs to the inlet to the travel trailer which is a 1/2" pex. I imagine all of these transitions cannot be good and perhaps I'm getting air in somewhere on suction side. All except the poly pipe was hooked up when I bought the trailer. The pump is spliced into the pex supply line and I didn't have a pex crimper so I'm just using hose clamps to attach it to the pump fittings on both sides.

    Also, the tank is outside on the ground and the pump has to lift the water about 4 feet if the water is low, then the lines drops down to the ground and the pump is mounted inside about 4 feet from ground level. Is this amount of lift causing a problem? The pump is rated for 9 feet of suction lift.

    Maybe I am getting air sucked in somewhere. There is no water leakage at all that I can find though. Someone mentioned something about possible cavitation but I am unaware of what would cause that.

    I am thinking I will replace the supply line from the pump all the way to the tank with 3/4" poly, except the tank drop pipe, and go from there. This would get rid of the pex and all of the different pipe transitions.

    Thanks in advance for any feedback!
  2. valveman

    valveman Moderator Staff Member

    Messages:
    4,586
    Location:
    Lubbock, Texas
    I think you have a air leak on the suction side.
  3. cursethebanksters

    cursethebanksters New Member

    Messages:
    9
    Location:
    Arkansas
    I'm going to replace the entire suction line with 1/2" line and go from there.
  4. valveman

    valveman Moderator Staff Member

    Messages:
    4,586
    Location:
    Lubbock, Texas
    Suction lines need to be larger than the discharge line. 3/4" discharge, use 1" suction.
  5. cursethebanksters

    cursethebanksters New Member

    Messages:
    9
    Location:
    Arkansas
    This pump has 1/2" inlets and outlets. It's been pointed out to me that running a 3/4" suction line on a pump designed for 1/2" might severely affect the suction. I'll get rid of all of the transitions and 3/4" line, replace it all with 1/2" and go from there. Hopefully that will solve everything. I also plan to reinstall the check valve in the tank because it definitely works better with it in there.
  6. valveman

    valveman Moderator Staff Member

    Messages:
    4,586
    Location:
    Lubbock, Texas
    I would think the 3/4" suction would be better. Again, the suction is usually one size larger than the discharge. You need bigger pipe on the suction because it is harder to draw water than to push water.
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