Abstract: A power generation system having a low pressure source of water, means connected to the source of water for pressurizing the water to a substantially higher pressure, means for forming steam from the pressurized water, and a steam turbine for deriving mechanical motion from the steam. The pressurizing means uses first and second chambers of variable volumes. Valve means are associated with the first and second chambers so that water flows into the first chamber when its volume is expanding but water is not allowed to flow into the first chamber when its volume is contracting. Likewise, the valve means are utilized so that water flows into the second chamber when its volume is expanding but water is not allowed to flow into the second chamber when its volume is contracting. Furthermore, valve means are associated with the first chamber to allow pressurized water to flow out of the first chamber when its volume is contracting.