A gas supply system primarily designed for use with fire sprinkler systems which includes a control system which uses flow demand to automatically determine the mode of operation and switch between providing air and nitrogen. The gas supply system can operate either in standard nitrogen generation mode where nitrogen is supplied to the reservoir tank and/or sprinkler system or in a bypass mode, where sufficient pressure is only obtained by directly supplying air. The gas supply system can provide for improved safety in operation as well as the ability to operate the sprinkler system primarily when filled with nitrogen supervisory gas.