It looks like some good help you have here...

I don't really know what my problem is. I have a pump made by Jacuzzi in my basement. I believe it is a shallow water jet pump. It's probably been sitting for 15 years without use. I took it apart got it running, put it back together, and tested it with a bucket of water and it works well (good suction pressure at the inlet). On its inlet, there is a brass spring-check valve. I put a weight on a string and estimate the bottom of the drop pipe to be a bout 15 feet. When I fill the drop pipe with water, it holds water, so I believe I have a foot valve at the bottom. However, when the pump is hooked up to the pipe (and primed) it will only pump a bit of water. If I take the pump back off, the water is still in the drop pipe.

I think that the foot valve might be stuck shut. Does that make sense? How is that repaired?