6.7.1 Radial running clearances shall be used to limit internal leakage and, where necessary, balance axial thrust. Impeller pump-out vanes or close axial clearances shall not be used to balance axial thrust. Renewable wear rings shall be provided in the pump casing. Impellers shall have either integral wear surfaces or renewable wear rings.
径向运行间隙应用于限制内部泄漏，并在必要时平衡轴向推力。背叶轮或紧密的轴向间隙不得用于平衡轴向推力。应在泵壳内安装可更换的耐磨环。叶轮应具有整体耐磨表面或可更换耐磨环。
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解释：背叶轮Impeller pump-out vanes，如下图的back vane 所示。Wearing ring见下图，如果叶轮材质非常耐磨，叶轮侧的wearing ring可以不要。
工程中，常用的平衡轴向力的手段有，多叶轮对称布置，双吸叶轮，叶轮上开平衡孔，调整口环的位置，适用平衡盘或者平衡鼓。老外的机组基本没有平衡盘，全都是平衡鼓，因为平衡盘是通过轴向间隙来平衡轴向力的，这在本标准中是不允许的。如下图，平衡盘就是靠着b0的间隙来控制平衡力的。
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6.7.2 Mating wear surfaces of hardenable materials shall have a difference in Brinell hardness number of at least 50 unless both the stationary and the rotating wear surfaces have Brinell hardness numbers of at least 400.
除非固定磨损面和旋转磨损面的布氏硬度都至少达到 400，否则可硬化材料制作的配对磨损面的布氏硬度至少应相差 50。
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解释：也就是说，泵口环和叶轮口环应该有一定的硬度差。国内很多厂家的耐磨口环的材质都是12cr13，很多不满足50的硬度差的要求。
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6.7.3 Renewable metallic wear rings, if used, shall be held in place by a press fit with locking pins, screws (axial or radial), or by tack welding. The diameter of a hole in a wear ring for a radial pin or threaded dowel shall not be more than one-third the width of the wear ring.
如果使用可更换的金属耐磨环，则应使用锁销、螺钉（轴向或径向）或粘焊进行压入固定。耐磨环上径向销钉或螺纹镙栓孔的直径不得超过耐磨环宽度的三分之一。
6.7.4 Nonmetallic wear rings may be installed in holders or directly into the casing. If suitable data exists showing that a press fit is sufficient for prevention of rotation and with purchaser approval, other mechanical anti-rotation features are not required.
非金属耐磨环可安装在支架上或直接安装在泵壳内。如果有适当的数据表明压入式配合足以防止旋转，并经买方批准，则不需要其他机械防转功能。
6.7.5 Running clearances shall meet the following requirements.
运行间隙应符合以下要求。
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解释：要求最小间隙的原因是为了防止发生卡死。虽然较小的间隙可以提高泵的效率，但是也存在动静部件接触的风险。尤其是对于高温运行的泵。
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a) When establishing internal running clearances between wear rings and other moving parts, consideration shall be given to pumping temperatures, suction conditions, the liquid properties, the thermal expansion and galling characteristics of the materials, and pump efficiency. Clearances shall be sufficient to assure dependability of operation and freedom from seizure under all specified operating conditions.
在确定耐磨环和其他运动部件之间的内部运行间隙时，应考虑泵送温度、吸入条件、液体特性、材料的热膨胀和咬合特性以及泵的效率。间隙应足以保证在所有规定的工作条件下，都能可靠地运行和不发生卡死。
b) For cast iron, hardened martensitic stainless steel, and other materials with similarly low galling tendencies, the minimum diametral clearances given in Table 6 shall be used, unless otherwise approved by the purchaser. For materials with higher galling tendencies or for all materials operating at temperatures above 500 °F (260 °C), 0.005 in. (125 μm) shall be added to these diametral clearances.
对于铸铁、硬化马氏体不锈钢和其他具有类似低咬合倾向的材料，应使用表 6 中给出的最小直径间隙，除非mm买方另行批准。对于具有较高咬合倾向的材料或在 500 °F (260 °C) 以上温度下工作的所有材料，应在这些直径间隙的基础上增加 0.005 英寸 (125 μm)。
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解释：奥氏体不锈钢就是一种高咬合倾向的材料。
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NOTE If materials with higher galling tendencies are operated at temperatures above 500 °F (260 °C), adding
0.005 in. (125 μm) to the diametral clearances in Table 6 is typically done only once.
注：如果具有较高咬合倾向的材料在 500 °F (260 °C) 以上的温度下工作，则在表 6 中的直径间隙中增加 0.005 英寸（125 微米）。表 6 中的直径间隙通常只需增加一次
- c) For nonmetallic wear-ring materials with very low or no galling tendencies (see Table H.3), as well as other wear-ring material combinations with proven operating experience, clearances less than those given in Table 6 may be proposed by the manufacturer to improve pump efficiency. Factors such as distortion and thermal gradients shall be considered to ensure clearances are sufficient to provide dependability of operation and freedom from seizure under all specified operating conditions.
对于咬合倾向极低或没有咬合倾向的非金属耐磨环材料 （见表 H.3），以及其他具有成熟运行经验的耐磨环材料组合， 制造商可建议采用小于表 6 所列的间隙来提高泵的效率。应考虑变形和热梯度等因素，以确保间隙足以在所有规定的工作条件下提供可靠的运行和避免卡死。
NOTE There are published data showing successful applications of nonmetallic wear-ring materials with API clearances [see 6.7.5 b)] reduced by 50 %. Reasonable reductions in clearances are believed to be dependent on the materials applied and other service conditions, such as cleanliness and temperature.
注：有公开数据显示，非金属耐磨环材料的成功应用可将 API 间隙[见 6.7.5 b)]减小 50%。据信，间隙的合理减小取决于所应用的材料和其他使用条件，如泵送介质的清洁度和温度。
==Table 6 Minimum Internal Running Clearances==
==表-6 最小内部运行间隙==
