Regarding the impeller mouth ring

If the gap is too large, there is excessive leakage from the pump, resulting in reduced efficiency.

It’s completely possible, but I don’t agree with the reasons you gave; it’s still likely an issue related to gaps

If the gap is too small, considering using a mouth ring might be an option; however, pay attention to the amount of turning – too much of it can have a significant impact on the pump’s head and pressure. If the pump’s head is large enough, you can proceed with the turning without concerns. If there’s a risk of binding, opt for a smaller amount of turning

If it gets a bit too large from time to time, the gap will increase and efficiency will drop

You can try to get out of the car slowly; it will be troublesome if there are too many cars

I don’t think efficiency is an issue; the key is whether it can meet the requirements regarding flow rate and head. It’s a good idea, as suggested by some, to use a smaller amount of turning.

Scratching between the impeller and the mouth ring is generally not caused by bearing clearance; if the bearing clearance is that large, it’s likely the bearing can no longer be used Possible reasons for this phenomenon: 1. Improper assembly ； 2. Failure to meet tolerances during shoulder machining ； 3. The mouth ring is not centered on the rotation axis ； 4. If it is a multi-stage pump, increasing the flow rate may not be appropriate ； 5. The slenderness ratio of the shaft is too high, resulting in poor rigidity.

For such issues, you need to consider whether the mouth ring is concentric with the shaft; the solution should be to reinstall the mouth ring with a standard gap

Check what medium is being pumped: if it’s viscous material, use a smaller gap in the mouth ring； For water pumping media, the gap at the mouth ring should be larger. The people upstairs have already provided good analyses; I’d like to add this: from a technical perspective, could it be that low liquid levels frequently occur, leading to cavitation and thus wear on the mouth ring?

Can it really be determined that it’s due to the bearing clearance? Is it perhaps an improper selection of the clearance?

I think that although the shaft doesn’t bend, it doesn’t necessarily mean there has been a change in the condition of the bearings. If the ring at the pump inlet is damaged, it may lead to reduced efficiency and lower head pressure, as well as cause vibration in the pump； Two might not solve the problem. The reasons need to be analyzed and appropriate measures formulated in order to solve the problem. The reason might be a change in the bearing clearance; replacing the bearings with new ones can resolve the issue. If the shaft assembly is not aligned (due to problems with the mouth ring, bottom sleeve, large cover shoulder, or bearings), it is necessary to realign it.

It can be turned, but the amount of cutting must be well controlled.

1. Poor quality of pump manufacturing ； There is a deviation in the concentricity between the pump casing and the pump body; for new pumps, this issue should be addressed with the manufacturer, while if it’s an old pump with a new problem, then it’s a matter of poor repair quality. 2. Scratching between the impeller and the throat ring is generally not caused by bearing clearance; if the bearing clearance is indeed that large, all that’s needed is to adjust it (referring to the scraping between the impeller’s end face and the throat ring)

This issue is explained in a clear manner. Essentially, the mouth ring serves as a sealing element between the impeller and the pump casing; it is merely a common name for this component. The number of mouth rings varies depending on the design of the pump – some pumps have mouth rings at the inlet, while others also have them on the back side of the impeller. In multi-stage pumps, each stage has its own mouth ring. The main function of the mouth ring is to prevent fluid from flowing between the high-pressure and low-pressure areas, thereby reducing the backflow of high-pressure liquid into the low-pressure area. There are strict requirements regarding the gap between the mouth ring and the impeller, and this gap depends on the type and size of the pump! An excessively large gap will reduce the pump’s efficiency; in severe cases, it will lead to a decrease in head and flow rate, or even prevent the pump from operating properly! Because the pump shaft rotates with radial oscillation, too small a clearance can cause mechanical friction with the pump impeller! Therefore, when installing or maintaining the pump, the clearances must be checked strictly in accordance with those specified in the manual! It must be replaced when it exceeds the standard!