Abstract: There is provided a valve for a reversible heat pump system, including six ports and three flow paths for a refrigerant, the three flow paths being selectable between different pairs of the six ports, wherein: two of the three flow paths are non-restrictive flow paths; and one of the three flow paths is a restrictive flow path. There is also provided a reversible heat pump system, including: the valve; a compressor; a process heat exchanger having input and output sides through which refrigerant is supplied and discharged respectively; and a rejection heat exchanger having input and output sides through which the refrigerant is supplied and discharged respectively, wherein the valve interconnects the compressor, the process heat exchanger and the rejection heat exchanger such that a refrigeration cycle can be established.