Atlas Copco CR7.5 Reciprocating Duplex Air Compressor 51CFM 7.5HP 3Ph 120 GalNew. Old stock. Discontinued model. Duplex unit. Powered by two 7. 5 hp motors 3 phase 460V The CR Piston Range also comes in a two pump duplex design. A duplex design can be used to improve efficiency and or to create redundancy and give you a back up option inside a single unit. All models in the CR Series duplex piston range are cast iron, splash lubricated, 2 stage, compressors with a magnetic starter as standard and a maximum operating pressure