In an apparatus at a carding machine having a cylinder, working elements and displaceable holding elements, which determine the carding gap between the cylinder clothing and the working elements, a displacement device actuatable by thermal energy supply is provided for the working elements in order to compensate for changes in the carding gap that arise during operation, and at least one adjusting element cooperates with a fluid. Thermal energy is conveyable to the fluid. In order to keep the carding gap constant or substantially constant in a structurally simple manner, the fluid is expansible by thermal energy supply and the adjusting element is positionally displaceable by expansion and/or contraction of the fluid