I have some questions I’d like to ask everyone

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I’m new here. I heard that there are many experts around, so I’ve brought some questions posed by my teacher to ask everyone~~~ There are quite a few questions; please forgive me. 1: (1) What tolerance fit is used for the connection between the impeller and the shaft of common centrifugal pumps? Note: The answer that is the only one should be wrong. (2) What tolerance fit is used, as per standards, for the mechanical seal shaft sleeve and shaft? . (3) What are the characteristics of the inner bore of the modular mechanical seal shaft sleeve? 2: Classified by their operating mode, what category do the small-end bearings of piston compressors fall into? 3: Besides affecting their volumetric efficiency and the sliding bearing effect, what else does the gap between the impeller seal rings, the inter-stage seal rings, and other similar rings in centrifugal pumps affect? 4: Why must the inlet and outlet valves be opened simultaneously before starting an axial flow pump? Its flow rate cannot be adjusted by regulating the opening degree of its outlet valve. 5: In multi-stage pumps with slender rotors, phenomena similar to pumping out occur during operation, causing more severe damage to the pump. It is also not suitable for operation in media with low specific gravity that are prone to vaporization. Why? (Ignoring factors such as a large number of impellers, numerous friction points, and a slender shaft that is prone to bending; these are merely consequences and superficial aspects.) Training: For worm gears, how do one measure and adjust their relative positions during maintenance and installation? What kind of contact marks are considered acceptable? 6: (1) In piston compressors, where the connection between the piston and the piston rod is removed or installed using heating, why cannot the heating time be too long, especially when the piston is made of aluminum? (2) For piston compressors, during assembly, the clearance on the side of the piston rings is generally kept as large as possible ； The side clearance of the support ring is on the low side; it certainly can’t be just a matter of thermal expansion allowance. 7:1 – please think about why the multi-stage pumps that we have repaired (where the axial positioning of the impellers on the shaft is achieved by the end faces coming into contact with each other for positioning) often experience high levels of vibration and a short service life. Even though our assembly process is much more precise than that of the manufacturer, why are the results not as good as those obtained by the manufacturer? 2. Why is it said that *the conventional practice is to use the following method for adjusting the end faces of the impeller and short sleeves: (1) Each end face is lapped against the mandrel using an abrasive with a particle size of around 200 mesh. (2) Adjust the local area of the end face according to the orientation. It is not only ineffective and inefficient but also not very scientific. 8: Understand the structural principles of the novel contactless labyrinth-type isolation oil seal. 2. Based on the structural characteristics of this oil seal as well as the requirements for its installation and use, consider what adverse consequences might arise if the bearing in operation is damaged or if the installation and operational parameters are outside the specified limits. 9: Given conditions: direction of rotation of the gear, whether it is driven or driving, right-handed or left-handed. Use the fingers of the left or right hand to determine the direction of the axial force in a cylindrical helical gear drive. Thank you all