The Malvern automatic air vent is a pressure safeguard used to let unwanted air out of the system. The air vent is automatic by shutting itself off when water enters the device. The device works using a float, which is found inside the automatic air vent and as water enters, the float will rise with the water and the valve will shut. This will then stay shut until the water level decreases and the float drops with it. The vent will then reopen.