Vincent, Pete_1
The compressors used for cascades and autocascades are standard units. The oil used needs to be capable of surviving the low temperatures of the final stages (Zerol 150 for example). A typical set of refrigerants used for a standard 3-stage cascade could be R404A, R23 & R14. An expansion tank for the R14 stage would be useful in keeping the static pressure down (it also helps during the defrost stage too) but is not essential ! There is an expert on autocascades within RE. His member name is JTSTEN, he has a website: http://s-10tech.com which gives his contact details. If you are serious about designing a low temperature system, he could be your man. The autocascade systems we use are capable of driving relatively large meisner coils (cryo coils) in our vacuum chambers. These reduce the temperature from ambient to >100 Deg. C. within a few minutes and can also defrost the coil in a similar time.