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Causes and Solutions of Leakage in Mechanical Seals of Multistage Centrifugal Pumps
Mechanical seal water failure is one of the most common faults in multistage centrifugal pumps, making the mechanical seal of multistage centrifugal pumps one of the most critical and vulnerable components. The material of the mechanical seal used in multistage centrifugal pumps must be suitable for the liquid medium conveyed by the user. Fluororubber mechanical seals are usually used by pump manufacturers, while some manufacturers use nitrile rubber mechanical seals. If the corrosion is severe, a Teflon material mechanical seal must be used.
The first possibility of water seepage at the mechanical seal is the wear of the dynamic and static ring planes of the seal. There are six reasons that can cause wear of the dynamic and static ring planes of the seal:
1、 Reason one: tightening the installation too much. If the dynamic and static ring plane of the mechanical seal appears severely burnt, blackened, with deep marks, and the sealing rubber becomes hard and loses elasticity, this phenomenon is caused by tight installation.
Solution: Adjust the installation height. After installing the impeller, use a screwdriver to pull the spring. The spring should have strong tension and rebounds immediately after being released. There should be a 24 mm moving distance.
2、Reason two: the installation is too loose. If there is a very thin layer of scale on the surface of the dynamic and static ring planes of the machine seal, which can be wiped off and the surface has no basic wear, it is caused by the spring losing its elasticity, poor assembly, or axial movement of the motor.
3、Reason three: poor water quality with particles. Due to poor water quality containing small particles and high content of hydrochloric acid salts in the medium, abrasive wear is formed on the sealing surface of the seal, causing grooves, ring grooves, and other phenomena.
Solution: Improve water pressure or medium and replace the mechanical seal.
4、 Reason four: dry grinding caused by lack of water flow. This phenomenon is most common in pumps with foot valve installation forms at the negative pressure of the inlet, with air in the intake pipe and pump chamber. After the pump is started, high friction rotates at a high speed and produces high temperature, which cannot be cooled. When checking the mechanical seal, the spring tension is normal, the friction surface is burnt and blackened, and the rubber becomes hard and cracked.
Solution: Drain the air in the pipeline and pump chamber, and replace the mechanical seal.
5、Reason five: cavitation. Cavitation mainly occurs in hot water pumps. Due to the high temperature of the medium, steam is produced, and the steam in the pipeline enters the pump chamber at high places. This part of the steam cannot be discharged, resulting in a lack of water flow, dry grinding and seal failure. Install an automatic exhaust valve and replace the mechanical seal.
6、Reason six: assembly problems. When the pump cover is installed, it may not be flat, causing the shaft and the pump cover to be not vertical, so that the dynamic and static plane of the seal cannot match properly. After the pump is started for a short time, single-sided wear and seepage occur. It is also possible that the rubber parts are damaged or the surfaces of the dynamic and static rings are bumped during the installation of the mechanical seal.
Solution: Reinstallation, checking whether the pump cover is flat.
7、The second possibility of water seepage at the mechanical seal is the failure of the rubber in the mechanical seal. The reasons for the failure of the mechanical seal rubber are: aging, deformation of the rubber, mainly due to the high temperature of the medium in the hot water pump, which can dissolve the rubber, resulting in loose and rough surfaces, loss of elasticity, and seal failure.
Solution: Replace suitable rubber materials.
8、The third possibility of water seepage at the mechanical seal is caused by the static ring chamber of the pump cover. The main reason is the large machining dimensional error and the rough surface of the static ring chamber. The manifestation is spraying water from the axial direction, and there is a gap between the static ring and the inner hole, or the inner hole is rough, the static ring rotates, and the rubber wears.
Solution: Replace the pump cover. Or use raw materials to wrap around the outer ring of the static ring or apply sealing glue as an emergency measure.
9、The fourth possibility of water seepage at the mechanical seal is the poor precision, small size, roughness, and rust of the motor shaft neck. The main reasons are that the motor shaft neck (at the loose ring position) size is small, or the pump shaft is corroded due to the corrosiveness of the medium, or the pump has been stopped for a long time, and as the medium water, the electrode potential of the steel shaft and the cast impeller and pump cover is different, resulting in the original electrochemical reaction and corrosion of the shaft neck. The manifestation is the surface of corrosion with spots.
Solution: Polish the rusted surface with sandpaper, wrap it with raw materials, and put it into the moving ring as an emergency measure. The best method is to replace the shaft or add a shaft sleeve and machine it to restore it to the size of the original shaft.