An expansion tank is disclosed in which a non-return valve is fitted in an outlet port of the expansion tank to limit backflow of coolant into the expansion tank in the event that the pressure in the expansion tank falls below the pressure in a return conduit thereby preventing the expansion tank from filling with coolant. The universal display system can effectively produce high-resolution images from data received from both analog devices and digital devices such as televisions, personal digital assistants, and computer systems. The enhanced amplifier includes a signal preparation unit to divide and shape the input signal in order to compensate for non-linearities in the combined output signal. The system also permits user selection of a logical operator from a plurality of displayed logical operators for linking first and said second information item search terms.