Vapor Return Valve: Also known as the vapor equalizing connection or vapor equalization valve, this function is needed on all ASME propane tanks. They are usually deployed in case the liquid within the container gets pretty overheated and must be evacuated from the container. Get yourself a Quotation click here https://gregoryisblu.blogdomago.com/25932438/not-known-details-about-new-2000-gallon-propane-tank