Economical monoblock construction of high tensile strength gray cast iron. Hard chrome plated spool. Adjustable ball spring relief (1000 PSI to 3000 PSI). Open center to closed center conversion available on some models. For use with system flows to 20 GPM. For use with system pressures to 3000 PSI. Max design and test pressure 3000 PSI. In exposed environments, do not mount. with spool vertical and handle end down.