Improving　thermodynamic　efficiency　of　prime　movers　is　the　key　issue　for　efficient　utilization　of　low-temperature　heat　resources.　Single　screw　expander　may　be　a　good　candidate　because　of　its　many　good　characteristics.　Precisions　in　manufacture　and　assembly　are　very　important　factors　to　the　performance　of　single　screw　expanders.　In　this　paper,　the　shaft　efficiency,　volumetric　efficiency　and　gas　consumption　rate　of　the　single　screw　expander　prototypes　were　tested　and　discussed.　We　have　manufactured　three　prototypes　with　different　gaps　to　investigate　their　performance.　The　first　prototype　(A)　has　the　largest　gap,　and　the　second　one　(B)　has　the　smallest　gap,　the　third　prototype　(C)　has　the　medium　gap　configuration.　Experimental　result　of　the　prototypes　was　obtained.　From　the　experimental　data　of　prototype　A,　the　power　output　was　about　5　kW,　the　gas　consumption　rate　was　above　105　kg/kWh　and　the　volumetric　efficiency　was　below　20%,　the　shaft　efficiency　was　only　34%.　From　experimental　data　of　prototype　B,　the　mass　flow　rate　was　significantly　decreased.　The　power　output　was　only　1.4　kW　and　the　volumetric　efficiency　was　slightly　lower　than　prototype　A.　The　gas　consumption　rate　was　much　more　than　that　of　prototype　A.　From　the　experimental　data　of　prototype　C,　the　power　output　was　about　4.5　kW,　but　the　mass　flow　rate　was　sharply　decreased.　The　gas　consumption　rate　was　about　65　kg/kWh,　the　maximum　volumetric　efficiency　was　about　66%,　and　the　shaft　efficiency　was　about　60%.　The　experimental　results　indicated　that　prototype　C　of　single　screw　expanders　had　the　best　overall　performance,　which　may　be　further　improved　by　optimizing　its　configuration.　(C)　2013　Elsevier　Ltd.　All　rights　reserved.