Abstract: A gas/oil high-low pressure control apparatus having a helical bourdon tube sensing a gas control pressure and a gap sensor connected to a pressure indicator and rotating between high and low set point flags in which the gap sensor controls a pilot actuated valve which in turn controls a gas supply. A pressure regulator is connected between the gas supply and the inlet to the gap sensor and the outlet of the gap sensor is connected to the valve. The gap sensor outlet also provides a regenerative feedback signal to the regulator for providing a snap acting closing operation of the valve when the gap sensor detects a set flag. The gap sensor is of a thermoplastic having an aligned inlet and outlet with a closible opening aligned with the inlet and the outlet for periodically cleaning the inlet and the outlet. The linkage between the bourdon tube and the gas sensor includes first, second and third links with a zero adjustment, a span adjustment and a linearity adjustment and an overrange protector.