driven well point screen / slot size question

Discussion in 'Pumps and Tanks Well Forum & Blog' started by too old for this, Feb 17, 2010.

  1. too old for this

    too old for this New Member

    Messages:
    5
    Location:
    toledo ohio
    Hello all. Must say this is a great source of knowledge. I have been reading (viewing) this site for over three years and have learned a tremendous amount to date.
    I now have a technical question regarding screen-slot size (for bob) or anyone else that can help.
    I have 2 inch shallow well point with 12'-6" of pipe and a 4' campbell 80 gauze point for a total depth of 16'-6".
    Depth to water is 9' in the summer and 10'-6" in the winter.
    This is connected to a Teel 3/4 hp pump rated at 17.5 gpm at 40 psi at 10' depth to water. The well was developed by running a jet pump to full prime / flow, and then opening a valve to let the water drop / surge the screen. Repeatedly.
    I only get 4.75 gpm max flow.
    The suction line is vaporizing /pump cavitating. I verified this by installing a sight glass on the suction pipe as well as a vacuum gauge. The sight glass shows air bubbles and the vacuum gauge reads 27-28 " Hg. There are no air leaks on the suction pipe. I verified this by submerging all fittings in water while the pump was running and still had air bubbles in the suction pipe.(viewed by sight glass) also could hear it in the pump. When I throttle down the discharge to a rate of 4.5 gpm, the bubbles disappear.
    I was convinced that the 80 gauze point was the restriction in the system, so I pulled the point.
    The point has crescent shaped perforations in the pipe where sand remained as the point was removed from the ground. I sampled some of the sand and measured the grains with a dial caliper. 10% of the grains were .012" : 80% of the grains were .016" : 10% of the grains were .018-.022". I also noticed a considerable darkening of the sand located at the very tip of the point. I am assuming this is a hard pan layer as I recall the first time I was installing this rig...it required a jack hammer (literally) to get the pipe past this depth.
    What point would be the best match for this system? I would like to get maximum performance from one point as space in my equipment room is extremely limited and installing a second point is (from a practical matter) out of the question. Would a 2" 12 slot be the best? What kind of gpm could I expect? There are no Johnson distributors locally that I know of. Does bob or anyone else have something they want to sell? (so long as it's the right solution)
    Thanks, and I am....too old for this.
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