Scheme of the refrigerator circuits (Courtesy of CryoConcept). Green: pre-cooling mode. Red: dilution mode. C = compressor, P = pump and MC = mixing chamber. Black: 4 K-tank of the refrigerator, fed by the 4He main reservoir. During the pre-cooling mode, the valve positions are: (1) and (5) = open; (2), (3) and (4) = closed; P = off and C = on. For the dilution mode, the valve positions are: (1) and (5) = closed; (2) and (3) = open; P = on, C = on; and (4) = open only for the pre-cooling circuit purging.