| 摘要 |
A linear turn down metering valve for gaseous fuels comprises a valve body having a frustoconical valve chamber receiving a rotatable valve plug and including an inlet on one side and an outlet at one end opposite a control shaft at the opposite end. The frustoconical valve plug is rotatable about a central axis aligned coaxially with an outlet end adjacent the chamber outlet. The valve plug includes an annular side wall defining a central bore and normally closes off the valve chamber inlet when the plug is in an "off" position. The valve plug is formed with a maximum flow, inlet port movable into alignment with the chamber inlet when the valve plug is initially rotated out of the off position to a maximum flow position. The plug includes a pair of generally transversely oriented divergent/convergent flow passages spaced from the valve plug inlet port providing decreasing flow area overlapping with the valve chamber inlet as the plug is rotated from the maximum flow position through a range of intermediate, angularly spaced flow control positions providing a linearly decreasing gas flow rates until reaching a minimum flow rate at the end of the range. The valve plug also includes a separate minimum flow passage system in communication with an adjustable flow control sleeve valve for providing an adjustable minimum flow of gaseous fuel when the plug is rotated to a minimum flow position beyond the intermediate linearly decreasing flow control range.
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