What is a cylinder flange?

A flange is a device that limits the amount of air entering a pump from the hot water cylinder. When water is heated, or replaced within the hot water cylinder, air bubbles are formed and collect around the side or the top of the cylinder.

If you are installing a pump, you need to ensure these air bubbles are not drawn into the pump.

By installing a flange, these air bubbles are prevented from entering the pump, as the flange can draw water from deeper within the hot water cylinder, allowing the air to pass up and out via the expansion vent pipe.