Abstract: A valve having dual seats and dual poppets operating in series to function as either a conventional check valve, or may be operated by an independent piston which may be styled to either combine or eliminate the check valve feature. One seat poppet combination employes a metal-to-metal seal. The other seat poppet combination utilizes a resilient o-ring seal vented so that when the seal is raised from the bottom of its groove, the upstream and downstream sides of the soft seat poppet can communicate. Alternative embodiments provide a family of zero leakage valves for different purposes, e.g. a check valve, pilot operated check valve, and an in line or balanced relief valve with or without the check valve feature by employing generally the same elements with modifications.