Abstract: A devise useful to transport thermal energy from a hot zone to a cold zone, over distance, and around or through obstructions, comprising: evaporator (101), switch-valve assembly (300), two condensers (501), (502), check-valves, interconnecting passageways, and a liquid-vapor phase-change working fluid. The motive power causing the devise operation is exclusively thermal. Thermal energy is continuously accepted at the evaporator and continuously rejected at the condensers. The switch-valve directs vapor through open ports to one condenser at a time. The vapor pressure in that chamber increases and creates a pressure differential between the two condensers. When this difference in pressure reaches a predetermined magnitude, the switch-valve changes condensers. The evaporator vapor pressure is pulled low by the newly opened condenser and the higher vapor pressure in the just closed condenser pumps its condensate back to the evaporator. The cycle continues alternating between condensers.