Performance. Figures 25 and 26 show typical efficiencies of all
single-screw compressor designs.
High isentropic and volumetric efficiencies result from internal compression,
the absence of suction or discharge valves and their losses, and extremely small clearance volumes.
The curves show the importance of selecting the correct
volume ratio in fixed-volume-ratio compressors.
Manufacturers’ data for operating conditions versus speed should
not be extrapolated.
Screw compressor performance at reduced
speed is usually significantly different from that specified at the normally
rated point because of the significant effect of leakage.
Performance data normally include information about the degree of liquid
subcooling and suction superheating assumed in data.