A cooling device (40) includes a heat exchanger (50), a first flow loop (52) connecting a cold sink (42, 44, 46) and the heat exchanger, and a second flow loop (54) connecting a hot sink (20) and the heat exchanger. A first passive one way valve (62) disposed on the first flow loop is oriented to allow flow in an allowed direction of flow (F1) and to block flow in the opposite direction. A second passive one way valve (64) disposed on the second flow loop is oriented to allow flow in an allowed direction of flow (F2) and to block flow in the opposite direction. The allowed directions of flow produce counter-flow in the heat exchanger. In an illustrative embodiment, the hot sink is comprises a cryogenic magnet coil (20) and the hot sink is a cold head (42, 44) and liquid helium tank (46).