A valve (4) for a refrigeration system. Comprises two diaphragms (8, 10) being operatively connected. One diaphragm (8) is in contact with the refrigerant, the other (10) is in contact with the filling fluid. The two diaphragms (8, 10) may have different active areas. In combination with the connection between the two diaphragms (8, 10) this provides a ‘pressure gearing’ between the filling fluid and the refrigerant. Allows the pressure of the filling fluid to be relatively low even when the pressure of the refrigerant is high, while ensuring that the valve (4) can function properly. Particularly suitable for high pressure refrigeration systems, such as CO2 systems.