| 摘要 |
PURPOSE:To effectively prevent the unstable control of a flow rate in a low flow rate area by providing a large-caliber valve and a small-caliber valve on a flow path in parallel with each other and at the same time applying a rational control form. CONSTITUTION:It is automatically decided by a deciding means 14 whether or not the flow rate changing rate of a flow path is increased to cause a state where a problem is produced with the controllability against the change of the valve opening amount with the flow rate control done by a large-caliber valve 2 based on the comparison between a calculated flow rate and a set flow rate serving as a standard of decision or the comparison between the detected opening amount of the valve 2 and a set opening amount serving as a standard of decision. The flow rate control is carried out by a small-caliber valve 4 only in a low flow rate state. Thus, it is possible to effectively suppress the flow rate changing rate of the flow path against the change of the valve opening amount as well as the increase of the pressure change in a low flow rate area. While the flow rate control is carried out by the valve 2 in a non-low flow rate state so that a wide control range is secured.
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