The current trend for ever increasing energy prices acts as an important driver for improved efficiency via novel heat integration and energy generation schemes. This project is concerned with small-scale Organic Rankine Cycle (ORC) engines for power generation, primarily for use in the domestic sector and in small industrial plants, in conjunction with solar collection and/or waste heat recovery. The reciprocating expander is a low-cost, low-maintenance, and readily available prime mover option for these engines, with promising performance characteristics (e.g. efficiency). An experimental test-bed is devised to study the efficiency and performance of a reciprocating piston-expander, operating with working fluids such as R245fa. This test-bed has a thermal power output of up to 20kWth giving a maximum mechanical output of 3kWe, with the inlet pressure of the working fluid limited to 10 bar. The tested expander is based on a commercially available unit intended for air compression applications, and is reconditioned for the purposes of the present test. Special consideration was given to the development of the expander valves. In addition basic cycle analysis and optimization is conducted.