Topaz Differential Valves are float operated water valves, ideal for use in water tanks which are filled by a pressure system controlled by a water pump. The valve gives a level difference which is adjustable from 2" to 98" to minimize the starting and stopping of the pumping system. The valve mounts near the top of the tank and fits easily though most tank walls (has long threads and a back nut with washer). As the tank empties, the weighted float travels down the cord until it hits the bottom stop. The valve then opens to give a full flow. As the water rises, the weighted float rises up the cord until it catches on the adjustable top stop, lifting bottom stop, causing the valve to close. Both the bottom stopper and the Top Stopper are adjustable. The full flow and positive on/off action reduce pump running and reduce water hammer. Available in sizes from 1/2" up to 1.25". Patented 1/4 turn removable base. NSF 372 Certified for potable water systems.