Single Stage = one Compressor.
Double Stage (Cascade) = two Compressors.
Triple Stage (Compound System) = 3 Compressors
No this compressors are not individually double stages.
Single stage Temperature range -50F. With single Refrigerant
Recommended; R-404/507/502 or equivalent
Single stage Temperature range -95F. With mix Refrigerants R-12 & CO2. The
R-401 can be substituted that is equal to R-12.
(134 not suitable) Person must be well acquainted with refrigerants to use
substitute in mix systems.
Double Stages (Cascade) temperature range -128F. With refrigerants
R-404/507/502 & 503/508B. This temperature can give problem with oil; make
sure that your oil is coming back to compressors.
Low stage 503/508B most use oil additive. A specially with capillary T.
Air/water cool, Capillary or TXV. Above 1HP recommended TXV
Triple Stages Compound system single Refrigerant R-404 or equivalent
All system above can be made to operate from around+400F. Down to low
number shown and at any giving point, with temperature control of 1Deg. +