A thermally responsive power device is disclosed employing a thermally sensitive unit in which are housed multiple vapor/gas filled capsules which expand and contract in response to temperature changes. The thermally responsive element is connected in a closed system through a conduit or tube to a remote diaphragm power or motion producing unit, and a temperature stable hydraulic fluid filling the space with the system moves the diaphragm in accordance with the expansions and contractions of the capsules. Several different embodiments for the capsules and their housings are shown, and all embodiments contemplate selective use of capsules with different vapor/gas fills to tailor the completed thermally sensitive elements to provide substantially equal temperature sensitivity in two or more regions of their working temperature range.
