国际标准化组织(ISO)将离心泵分为三类: I类技术泵，要求最严，即石油及石油化工用系; II类技术泵，要求中等，即化工用泵;III类技术泵，要求最松，即一般清水泵。本章主要介绍要求较高的离心泵设计，其他两类简单阐述。设计人员可根据实际情况(包括表面粗糙度、尺寸配合精度、几何公差、间隙、技术要求等)灵活运用。对于高压锅炉给水泵、军工用泵、核电用泵等，即便是输送清水，也绝不能简单套用上述划分方式，它们都有各自的标准，设计人员需根据具体要求酌情处理。
2) 静平衡处理。一般静平衡G6.3 级，有时要转化为克验收(见本书 7.6.1)，不平衡质量允差可以按表6-1 选取。
Parts Design of Slurry Pump
The International organization for Standardization (ISO) divides centrifugal pumps into three categories: Class I technical pumps, which are the most stringent, namely, petroleum and petrochemical systems; Class II technical pump, with medium requirements, i.e. chemical pump; Class III technical pump, with the most loose requirements, is the general clean water pump. This chapter mainly introduces the design of centrifugal pumps with high requirements, and the other two categories are briefly described. Designers can flexibly use it according to actual conditions (including surface roughness, dimensional fit accuracy, geometric tolerance, clearance, technical requirements, etc.). For high-pressure boiler feed water pump, military pump, nuclear power pump, etc., even if it is used to transport clean water, the above classification method must not be simply applied. They all have their own standards, and the designers need to deal with them according to specific requirements.
6.1 Parts design of single-stage pump and two-stage pump
As shown in Figure 6-1, the common impeller structure type can be integral casting forgings or weldments.
1. Closed impeller design
The structure of closed impeller is shown in Fig. 6-1a~c.
1) See Table 2-2 for technical requirements for heat treatment of materials and castings.
2) Static balance treatment. Generally, static balance grade G6.3 is sometimes converted to gram acceptance (see 7.6.1 of this book), and the tolerance of unbalanced mass can be selected according to Table 6-1.
3) The processing of front and rear cover plates shall be inspected with a sample plate, and the surface roughness shall meet the requirements of 2.5.3 of this book.
4) Generally, there are sealing rings on the front and rear cover plates of the impeller, and many of them are also embedded with the rear cover plate impeller sealing ring. Clean water pump and chemical pump generally do not need to insert the back cover impeller seal ring. See 7.7.3 of this book for the fixing method and matching of sealing ring.
5) The fitting tolerance between impeller and shaft is H7/h6.
6) When there is a rear seal ring (see Fig. 6-1a), the total area of the balance hole shall be 3~4 times of the annular area of the rear seal ring gap.
7) When there is no rear sealing ring (see Fig. 6-1b), the balance axial force of the back blade is generally increased. However, API 610 does not recommend the use of back blades to balance the axial force, because this method is not reliable
8) When the pump lift is not high, there can be no rear seal ring (see Fig. 6-1c) or back blade, and the smaller axial force generated by the pump can be borne by the rolling bearing.
9) At the outlet of the front and rear cover plates, there is no chamfer (see Fig. 6-1f), which is convenient for dynamic and static balancing and weight removal.
10) Impeller fixation: flat key is used for radial fixation, and impeller nut is used for axial fixation
2. Semi open and open impeller design
The design of semi open impeller and open impeller is shown in Fig. 6-1d and e.
Impellers have only one cover plate. Generally, there is no front cover plate, and some have no rear cover plate. Many technical requirements are the same as those for closed impellers. The differences are described as follows:
1) When the impeller is open, the exposed blade and the corresponding wear plate shall be processed and inspected with a sample plate.
2) After finishing the processing of wear plates and exposed blades, they shall be grinded and painted for inspection. The uniform contact area shall not be less than 50%. Once this work is done, it must not be neglected.