Abstract: A gas generating system (S) has a plurality of product gas generating modules (18) each of which comprises a plurality of molecular sieve beds (bed 1, bed 2) generating a product gas acting in a repetitive cycle with each cycle having a period of the cycle with peak product gas flow (106). A manifold (52) combines the product gas from the plurality of modules (18). The processor (58) generates a control signal that is communicated to the gas generating modules (18) such that the peak product gas flow period (106) of the repetitive cycle of the modules (18) is adjusted in response to the control signal. The processor (58) causes the peak period (106) for the modules (18) to be timed across the repetitive cycles in a controlled distribution.