Abstract: A liquid level controller for a waterpan-type spray booth. The controller comprises a normally-open first air pressure sensor and switch for detecting a minimum level of negative static pressure through the restricted opening indicative of ventilation fan operation and for closing the first air pressure sensor and switch to thereby permit a voltage output. A normally-closed second air pressure sensor and switch is provided for sensing a predetermined negative static pressure level indicative of a minimum adequate air flow through the restricted opening for opening the second air pressure sensor and switch to interrupt a current flow through the second sensor and switch. The normally-closed second air pressure sensor is normally closed by the voltage output from the normally-open first air pressure sensor and switch. The first and the second air pressure sensor and switch are operatively connected to a water supply valve.