Thank you to those of you who played along with my post last week asking what you thought the pictured object was.
I had a couple of friends in IRC guess (or at least get close to guessing) that it was a check valve. I pulled it off the end of the pipe that goes into my cistern.
My water pump had been making an awful racket and needed to be re-built. It really is a simple thing and I got a recommendation for a man to rebuild it. Though, like always, it took longer than he had said it would take. After getting the pump back from the repair shop, I discovered that probably the reason the pump had gotten worn out and needed new bearings and seals was that it was not holding its prime. The pump itself is not responsible for keeping primed, rather there is a check valve that keeps the water in the pump. That valve, the one pictured, was worn out.
To disconnect the pipe that held the check valve, I had to get into the cistern. Not fun! I was thinking that was what it would take, but did not want to take the plunge without a second opinion. I called a friend to come and help me. He agreed that getting into the cistern was the only way to get enough leverage on the pipe with the pipe wrench. Down I went. I checked for spiders and scorpions as soon as I got in. There was only one spider and it was a good distance from me. So I let it live.
After getting the pipe out and replacing the check valve, it was a simple mission to put it all back together. It took several hours, but was only a $12 repair.
The new check valve is brass and plastic–not near as decorative as the copper one that I took off. I will keep the copper one just because it is neat looking. I might be able to incorporate it into some fancy montage in my retirement home.