Pressure relief valves

I would hate to tear these apart not knowing if there is a market for used pressure relief valves. I have 2 large ones with 3 inch by 2 3/4 connections. They are 15 inches long and weigh 15.2 pounds each. They look to be open links they did there job. Called a Kunkle valve made by navsi. They manufacturer doesn't buy they back. This size retails for 500.00 I think.