All mains shall contain a valve at least every 1000 feet. A valve shall be installed on at least two legs of every main tee. A valve shall be placed near the end of any dead-end main provided that at least one joint of pipe shall be placed beyond the valve and anchored. This final joint shall also contain a means of flushing the line. Valves deeper than 36" shall employ valve extensions to within 36" of the ground surface. Valve nuts shall be covered with three-piece adjustable cast iron box covers set to grade. All valves shall be right-hand turning to close. Valves 12" and smaller shall be Mueller A-2370 Resilient Seat Gate Valves, or approved equal. Larger valves shall be Mueller Line Seal III Butterfly valves, or approved equal.