There is provided a method for generating power from a working fluid wherein the working fluid is a saturated vapor or is superheated to a vapor and then passed to a high pressure zone where the working fluid is used to impart work to a working shaft by means of directly linked high and low pressure cylinder piston assemblies located in the high pressure zone and a low pressure zone, respectively. Work is imparted to the working shaft rotatably coupled to the high pressure piston by constantly exposing the lower face of the high pressure piston to the vapor in the high pressure zone while selectively exposing the upper face of the high pressure piston to the vapor in the high pressure zone as the high pressure piston approaches upper dead center in relation to the working shaft, said upper face of the high pressure piston forming a first variable volume with the high pressure cylinder wall; and concurrently therewith intermittently discharging vapor from the first variable volume to a larger second variable volume formed of the lower face of a low pressure piston linked directly to the high pressure piston and a low pressure cylinder wall while constantly exposing the upper face of the low pressure piston to low pressure vapor in a low pressure zone and intermittently exposing the second variable volume to the low pressure zone, said second variable volume being allowed to increase more rapidly than the first variable volume decreases as the high and low pressure pistons move from bottom dead center to top dead center in relation to the working shaft.