A power tool includes a tool head having a working element and a powerhead configured to provide power to the working element. The powerhead includes a fluid tank configured to hold a combustible fuel and defines an initial internal volume having an internal pressure. A diaphragm is formed of a flexible material and forms at least a portion of the fluid tank. The diaphragm moves from an unexpanded state to an expanded state when a temperature of the combustible fuel increases above a threshold value. Movement of the diaphragm to the expanded state increases the internal volume of the fluid tank to allow the internal pressure of the fluid tank to remain approximately constant.
