In an earlier paper (1)†, the author discussed the nature of pressure pulsations in suction systems of free-piston gas generators, and in particular various forms of pulsation damping devices. A theoretical approach was based on a simple linear treatment of the system, i.e. (1) regarding all pressure pulsations as small in relation to the mean pressure on which they are superimposed, (2) treating dissipative elements (pipe friction or concentrated restrictions) as having linear pressure drop-velocity relationships about the mean flow condition, and (3) treating all distributed elements as having wave motion in accordance with small wave (2) or acoustic theory (rather than the non-linear finite wave theory (3) (4)). Although the physical conditions in compressor delivery systems are very different from those in gas generator suction systems, a similar theoretical approach, verified by acoustic model tests, has been found both to provide a good insight into the problem, and to give an acceptably accurate quantitative indication of pressure pulsation amplitudes. For this purpose systems have been divided into: (1) lumped impedance systems, (2) distributed impedance systems.