Adjustment of the cascade ratio and g-value for shielded pumps
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Our company has purchased several shielded pumps from Dalian Huanyou, such as the model NV32H-422JBMT-125-100-200. Does the number 422 here represent the frame number? It is said that the series parameter and the g-value of shielded pumps are adjusted based on the frame number. For this pump, I set the series parameter to 1.9 and the g-value to 4.6; after replacing the bearings and shaft sleeves twice, it only operated for one day and one night before the bearing monitor indicated a yellow status. The information provided by the manufacturer is not clear to us; we hope experts will kindly offer their guidance!
The serial number 1.9 is a bit high; based on practical experience, a value within the range of 0.8–1.5 results in a longer service life. The serial number values provided by our manufacturer in Dalian Empire are roughly the same as those mentioned by the poster. We tried to follow the manufacturer’s guidelines in the past, but found that the values were significantly too high. Over time, we determined that a range of 0.8–1.5 yields a longer service life, and the poster might find this useful as a reference
The g-value is divided into balanced and unbalanced impellers
The information provided by the manufacturer before was also from Dalian Empire.
Of course, what is being sought here is of the non-equilibrium type.
422 is the frame number; 1.9 you chose is indeed a bit large
The range it provides is on the high side, and its service life is short, which makes it convenient to make money from selling accessories; you should set the value at around 1-1.5 to ensure a longer service life. Additionally, for shielded pumps, it’s necessary to control the gap behind the impeller – if this gap is too small, the graphite bushings and thrust discs on the impeller side will wear out very quickly
Now the serial value has been set to 1.2 and the G value to 4.6; the performance is indeed much better than before. However, there are still slight changes in the bearing monitor. The interfoliar space you mentioned must refer to the g value. Are there any tricks for this?
The main shaft cannot be pushed towards the impeller side; a depth gauge is used to measure the gap between the impeller and the pump cover. If the gap is small, shims are added behind the shaft sleeve, which moves the impeller further away. Generally, the adjustment is only slight, as it’s more common to use shims on the graphite bearing on the impeller side to adjust the clearance – after all, it’s easier to add shims to that graphite bearing. The other option involves breaking something apart, which is more complicated. If, in order to control the axial shift, a 1mm shim is added to this graphite bearing, this means that the graphite bearing protrudes by 1mm compared to before; as a result, the thrust disc is blocked 1mm earlier, and the shaft shifts less towards the impeller side by 1mm, which in turn reduces the clearance at the back of the blades by 1mm. If it’s not too much trouble, it’s more scientific to add a shim to the other bearing in order to adjust the axial shift, as this won’t affect the clearance at the back of the blades. Slight changes in the bearing monitor readings are still acceptable; these can be caused by issues such as trapped air, unstable flow rates, air content in the medium, or excessive axial shift. As long as the readings don’t reach the red zone, it doesn’t affect normal operation.