Here's what the front side looks like.
Here's how the valve works, when pressure builds up on the water pump circuit, the valve is forced open and water flows around the opening. A very simple device, and a pretty easy one to work on.
After a light buffing on the brush wheel, and a light scrub with a gun cleaning brush, I soaked the valve in CLR to remove any corrosion. If you use a stainless steel brush, for instance, you'll leave lots of small scratch marks in the soft "yellow metal" and this will just attract debris.
The idea wasn't to make this part a show piece, but just to clean it up so it was free of junk and operated cleanly. This is a quick operation, and well worth the time to do it. The main issue now, is to get a gasket back in place so the valve closure piece won't leak.
Regards, Paul