The axial movement problem of horizontal multi-stage pumps
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Our company has newly installed several horizontal multi-stage pumps from Dalian Danai, featuring single-sided back-to-back double seals with internal flushing oil. Oil for flushing was leaking from one of the ends, and upon inspection it was found that the internal seal was damaged. After the new seal was installed, it was found that all the oil in the flushing oil tank at the front end of the pump had leaked into the pump chamber and flowed out through the inlet drain valve. Obviously, it was caused by the shaft shifting during the disassembly of the pump, which led to the failure of the mechanical seal on the inner side of the front end. Dear forum members, how should this situation be handled? Are there corresponding installation data available for the various components? What are the precautions to take when maintaining such pumps?
Before disassembling the pump, it is necessary to loosen the set screws on the seal positioning ring, so as to separate the seal shaft sleeve from the pump shaft; this way, even if the pump shaft moves, it will not cause any impact on the seal
This situation usually occurs because, when installing the mechanical seal, the balance disc is not in close contact with the balance plate; there is a gap between them. After the mechanical seal is installed, the balance disc and balance plate come into contact with each other, causing the shaft to shift forward and reducing the compression amount of the mechanical seal. During installation, it is important to first install the mechanical seal on the end where the balance disc is located, and to ensure that the balance disc and balance plate are in close contact. Only after both bearings have been installed should the set screws on the shaft sleeve be tightened.
It’s probably a problem with the installation of the mechanical seal; those gaps need to be properly controlled. Also, do not apply pressure to the seal oil of the mechanical seal when the pump is not running; the pressure applied should be in accordance with the specified requirements and must not be too high.
I’ve encountered this problem before. It is caused by shaft movement resulting from the removal of the non-drive-end bearing. The drive-end seal is not damaged; once the shaft is in place, it’s sufficient to add sealing oil to the drive-end seal oil tank. The solution is to block the gap between the pulley and the bearing housing at the drive end; I used screws to hold it in place. Whatever method you use, just make sure that the shaft doesn’t move around.