Flow rate range variable type flow rate control apparatus

A method of controlling fluid flow of a fluid supply system comprising the steps of:

• (a) providing a fluid supply system comprising a flow rate range variable type flow rate control apparatus comprising
• i. a first fluid passage for small flow quantity;
• ii. a second fluid passage for large flow quantity;
• and
• iii. switching means of switching fluid for flowing in a large flow quantity range and fluid for flowing in a small flow quantity range so that the first fluid passage and the second fluid passage are operably connected to a flow rate detection part of the flow rate control apparatus, wherein the switching means operates in a first mode to make fluid flowing in the small flow quantity range flow to the flow detection part through the first fluid passage for small flow quantity and to switch a detection level of a flow rate control part to a first detection level suitable for detection of fluid flowing in the small flow quantity range and the switching means operates in a second mode to make fluid flowing in the large flow quantity range flow to the flow detection part through the second fluid passage for large flow quantity and to switch the detection level of the flow rate detection control part to a second detection level suitable for detection of fluid flowing in the large flow quantity range;
• and
• (b) controlling a flow rate of fluid in the fluid supply system by operating the switching means in the first mode so fluid flows through a first orifice at a flow rate in the small flow quantity range and by operating the switching means in the second mode so fluid flows through a second orifice at a flow rate in the large quantity flow 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 the switching means installed on the second fluid passage in which the second orifice for controlling large flow quantity is disposed,
• and when controlling large flow quantity, a total flow quantity supplied to a fluid supply pipe of a pressure type flow rate control apparatus of the flow rate range variable 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.