Expansion vessel for a heating or cooling system

An expansion vessel for use in a fluid circuit of a heating or cooling system, said expansion vessel comprising a first internal volume, for receiving fluid from the fluid circuit, and a second internal volume, for containing air, said first and second internal volumes being separated by a diaphragm;

• said expansion vessel defines a fluid inlet port connectable to the fluid circuit of a heating or cooling system for receiving circulating fluid within said fluid circuit therethrough into the first internal volume of the expansion vessel, and
• said expansion vessel further defines a fluid outlet port connectable to the fluid circuit of the heating or cooling system for returning circulating fluid within the first internal volume of the expansion vessel therethrough to the fluid circuit;
• said fluid outlet port is separate from said fluid inlet port, and
• the fluid outlet port and the fluid inlet port are each provided with a non-return valve;
• whereby a one-way continuous fluid flow path through said first internal volume is defined, extending from the fluid inlet port to the fluid outlet port.