Abstract: A pivot arm is used in a liquid flow switch or liquid level device to transmit a force generated within a fluid chamber through the wall of the chamber to the outside. A pivot pin pivots the arm in a bore in an insert in the wall and a seal is provided in the form of a rolling diaphragm having its outer periphery sealed to the periphery of the bore and its inner portion sealed to the arm. Rocking movement of the arm is subject to very little resistance by the rolling diaphragm and yet the necessary fluid tight seal is maintained. The rocking movement is protected against contamination by a unique flexible boot and filter combination.