Nominal diameter and flow valves, basically the same breath for full-bore type, Circulation than nominal diameter valve is given. it small called non-reducing type.

流道孔径与阀门公称通经，基本相同的为全通径式；流通孔径比阀门公称通经小的称为缩径式。

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Causes responsible for bore polygonning of steel tube which appears as a defect during sizing and reducing are analyzed and common-used control methods therefor described.

简介了钢管定减径时内多边形缺陷产生的原因及其一般的控制方法。

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