Expansion tanks on water heaters provide the hot water inside with a place to go as it heats. Because most homes are now equipped with backflow prevention valves, water inside a hot water tank can no longer expand through the inlet pipes that come from the municipal water supply. Installing an expansion tank prevents too much pressure from building up inside your hot water supply system. These tanks contain air under pressure to handle the incoming water. The pressure in these tanks needs to be set at a specified level in order for them to work properly.
Set the expansion tank on a flat and level surface.
Determine the proper pressure for your expansion tank. This will depend on the size of your water heater and the temperature of the water inside. You can usually find this information in your water heater owner's manual.
Locate the recharge valve on the expansion tank. They are usually placed at the bottom of the tank. Remove the valve cover.
Slip a standard tire gauge over the valve. Make a note of the reading. Remove the gauge.
Attach a bicycle pump or electric pump over the recharge valve. Start the pump. Check the pressure inside the tank as you pump with the gauge. Stop pumping when the pressure inside the tank reaches the recommended level.
Replace the valve cover.