Importance

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Abstract

An automatic-control valve device has a main valve unit, and a pilot valve unit for controlling the main valve unit. The pilot valve unit has a pilot valve A which closes when pressure in a downstream passage on the downstream side of the main valve unit increases beyond a predetermined value, a pilot valve B which opens when pressure in the downstream passage increases beyond the predetermined value. The pilot valve A and the pilot valve B are connected in series by passages through a main valve driving pressure chamber in a section between an upstream passage on the upstream side of the main valve unit and the downstream passage, and cooperate to maintain the pressure in the downstream passage at the predetermined valve. A pilot valve C which closes when the pressure difference across an orifice disposed in a passage extending through the main valve unit is greater than a predetermined value is connected in series to a passage extending across the pilot valve A to limit the flow rate of a fluid in the downstream passage to a predetermined value. The respective valve elements of the pilot valve A and the pilot valve B may be held on a single valve stem. The orifice may be of a variable type. The automatic-control valve device may be provided with a valve means placed in a passage extending across the pilot valve A to open and close the passage according to the variation of a liquid level on the downstream side, and a valve means placed in a passage extending across the pilot valve A to close the passage upon the detection of an abnormal condition by an abnormal condition detecting means.

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First Claim