The Alm Automatic Filling with 1/2" Coupling + Manometer from Watts is an essential accessory for any heating installation. Designed to ensure the smooth filling of the system with water at the selected pressure, this device is necessary for balancing the pressure drop caused by air being released through the air vent valves. It is usually installed at the system inlet, between two shut-off valves, allowing for easy removal without the need to drain the installation.