Patent ID: 8418714

Claim:
A flow rate range variable type flow rate control apparatus comprising: (a) a pressure type flow rate control apparatus that operates to control flow rate Qc of fluid passing through an orifice according to the relationship Qc=KP 1 when a critical condition between P 1 and P 2 is present, where K is a proportionality constant, or the pressure type flow rate control apparatus operates to control the flow rate Qc through the orifice according to the relationship Qc=KP 2 m (P 1 −P 2 ) n when the critical condition between P 1 and P 2 is not present, where K is the proportionality constant, and m and n constants, wherein P 1 is an orifice upstream side pressure and P 2 is an orifice downstream side pressure; and (b) a first fluid passage disposed between a downstream side of a control valve and a fluid supply pipe of the pressure type flow rate control apparatus, wherein the first fluid passage comprises two second fluid passages arranged in parallel, wherein the two second fluid passages are provided with a plurality of orifices having different flow rate characteristics, wherein the plurality of orifices include a first orifice and a second orifice, wherein fluid flowing in a small flow quantity range is made to flow to the first orifice for effecting flow control of fluid flowing in the small flow quantity range, while fluid flowing in a large flow quantity range is made to flow to the second orifice for effecting flow control of fluid flowing in the large flow quantity range, wherein the second orifice controls large flow quantity and the first orifice controls small flow quantity, wherein a control range of fluid flow rate is switched either to the small flow quantity range or to the large flow quantity range by operating a switching valve installed on the one of the two second fluid passages in which the second orifice for controlling large flow quantity is disposed, and when controlling large flow quantity, a total flow quantity supplied to the fluid supply pipe of the pressure type flow rate control apparatus comprises the large flow quantity controlled by the second orifice and the small flow quantity controlled by the first orifice.