Corken vertical piston compressors with double piston rod seals (“D” series) have a spacer sleeve between two sets of piston seals. This design prevents gas leakage and contamination and significantly extends the service life, since in case of partial wear or damage to one of the seals, the tightness is maintained by the second set. This is especially important in oil-free reciprocating compressors, where the wear of the friction parts is faster.