Keeping a pump primed

I'm putting an old well pump in my pond for a fountain and watering the lawn. I think it is referred as a jet pump. I have a check valve at the end of a 20' intake pipe. But it doesn't keep it's prime. I have replaced the valve without sucess. Is this type of pump adaptable to this application?
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The pump seems to be in good order. The verticle lift is about 5feet. The intake is about 12" under water. While running, I can't see any leaks. One thought was after the pump stops running, a siphon starts from the fountain end and rermoves just enough water to loose the prime.
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The
One
fountain end

Although you don't describe how the fountain could siphon the water out of the pump's wet end.... especially with no air leaks in the tubing from the water source, which kinda makes that impossible, especially if the pump is lower than the water outlet at the fountain. But if so, then you should use a submersible pump. They make fountain pumps for just this purpose.
I think you have a problem on the suction end of this rig. Spray shaving cream foam around all suction joints and watch for it to be sucked in and as you run the pump. It will make little holes or dimples in the foam or suck a hole in the layer of foam.
Gary Quality Water Associates
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