Hello to the experts at "Ask This Old House". I am searching for a high quality check valve for use in a household well water system. We are drawing water at a depth of about 90 feet from a well that uses a submersible pump system and a pressure tank. The critical check valve between the submersible pump and the pressure tank leaks, allowing water to flow backward into the well. A number of new replacement valves, supplied by local hardware stores have been installed in the system and leak shortly thereafter. These valves use a swing-type gate, are made of brass and are of foreign origin. The faulty valves cause the system to re-pump unnecessarily and waste electrical energy. We are searching for an affordable 1.5" threaded check valve suitable for operation in a 70 psig (maximum) system. The hardware must be leak tight to reverse flow, compatible with drinking water and attainable in Northern California. Can you recommend a suitable product for this application? Many thanks from David.