(under the class definition) Apparatus having a cellular member rotatable about an axis with means to isolate therein and from its source a volume of gas to be pumped, transfer said volume to a position where a gaseous motive fluid may be admitted into said cellular member for the purpose of increasing the pressure of said volume while an interface is maintained between the two gases, and then permit the pumped gas and the motive gas to be exited from said cellular member each into a separate flow path.
