An apparatus for regulating temperature is presented. The apparatus comprises: a shell comprising a first cavity and a second cavity; and an inner valve body and an outer valve body disposed in the shell between the first cavity and the second cavity, wherein the inner valve body is movable relative to the outer valve body, and the outer valve body is movable within the shell. Depending on the temperature inside the shell, the inner valve body and the outer valve body can substantially seal the first cavity from the second cavity. The inner valve body and the outer valve body can also provide, respectively, a first flow path and a second flow path between the cavities, depending on the temperature.