An apparatus for treating workpieces comprises a treatment chamber enclosing a treatment zone for workpieces. A conveyor guides workpieces through the chamber. Said conveyor comprises drive elements located outside the chamber, and a carrier arm, extending through a slot along the conveyor's path of motion, in a wall of the chamber. A sealing arrangement comprises a first set of spring strips, which overlap laterally and are attached on one side of the slot to the wall, and an opposing second set of spring strips attached on the other side of the slot to the wall. In a resting position, the end zones of the spring strips overlap. Two deflecting devices, which move together with the carrier arm by the conveyor, open the sealing arrangement proximate the carrier arm by resiliently bending apart the spring strips. After passage of the carrier arm, the spring strips return to a sealing position.