# The slope ds/dT of the saturated vapour line in T–s diagram (see Chapter Classification of pure (single-component) working fluids) should be nearly zero, but never positive in the applied pressure ratio of the compressor. This prevents significant moisture (liquid droplet) formation or excessive superheat occurring during the compression. Compressors are very sensitive to liquid droplets. 
# The saturation pressure at the temperature of evaporation should not be lower than atmospheric pressure. This mainly corresponds to open-type compressors.
# The saturation pressure at the temperature of condensation should not be high.
# The ratio of condensation and evaporation pressures should be low.