Pirani gauges are used in an ac bridge circuit to sense deviation from the set point, and with the aid of a porportional leak valve, control the pressure of laboratory‐scale vacuum systems over the range of 0.1 to 10 000 &mgr; of Hg. Pressure fluctuations from the controller action are negligible and stability of ±1% has been obtained over long periods without operator attention. Set point is easily adjustable by panel control knob. Commercial components are used except for the leak valve which is of special construction.