就位接头与止动环用螺纹联结并上紧扣和钻柱连接下入井内，在未投入止回阀时作为钻柱上的一个接头。

The landing is thread connected with stop ring and tightened on and put into downhole with drill string. The landing sub is used as a sub above drill string before check valve is run in downhole.

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同轴、管内螺纹弹簧单导对夹式止回阀，专门用于防止水击作用和倒流现象。

The ALC? is an in-line, spring assisted, single guided "wafer" check valve designed to prevent "water hammer" and "reverse" flow.

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抗腐蚀、通用和可靠的弹簧止回阀，经济型、管内螺纹，适用于大部分设备。

The DFT? Model DLC? is a corrosion resistant, dependable, versatile and economical spring assisted, in-line check valve for a wide range of applications.

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