F04C 18/30

Rotary-piston pumps specially adapted for elastic fluids having the characteristics covered by two or more of groups [CPC: F04C18/02], [CPC: F04C18/08], [CPC: F04C18/22], [CPC: F04C18/24], [CPC: F04C18/48], or having the characteristics covered by one of these groups together with some other type of movement between co-operating members