A modulator (10, 10A) for changing a constant flow of gas to a pulsed or intermittent flow of gas, said modulator (10, 10A) including a housing component (11) and an insertion tube (15) for insertion into a hollow interior (16) of the housing component (11) wherein after insertion of the insertion tube (15) into the housing component (11), gas is generated either in situ within the hollow interior (16) of the housing component (11) and be caused to flow out of an outlet (23A) of the modulator (10, 10A) in pulses or alternatively gas is passed into the insertion tube (15) in a constant flow and upon reaching the hollow interior (16) of the housing component (11) is released therefrom through the outlet (23A) in a pulsed flow.
