A method and a pump apparatus are provided for the generation of an adjustable, substantially constant volume flow of a fluid by means of a pump apparatus, wherein the fluid (5) is forwarded by the pump apparatus (1) from a reservoir (2) into a flow connection (4). A rotary pump (1) is used as the pump apparatus and the rotary pump (1) is operated at an efficiency which is less than half the maximum efficiency (.eta..sub.max) of the rotary pump (1).