A fluid control system for delivery of a liquid includes a pneumatic drive that incorporates a linear actuator (115) to effect known volume changes in a gas reservoir (120). The gas reservoir is in fluid communication with a gas-side reservoir that is separated from a fluid-side reservoir by a flexible membrane. Movement of the linear actuator effects positive or negative volume differences on the gas in the gas-side reservoir, resulting in a decrease or increase in pressure of the gas that is transmitted to the fluid-side reservoir to draw fluid, primarily liquid, in from a source (130) or deliver liquid out to a sink. In another aspect, a mechanism is provided for the detection and elimination of air bubbles in the fluid path.