The multi-stage pump leaks heavily after it is stopped; analyze the reasons
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The unit is equipped with a multi-stage pump for liquefied gas; there is no leakage when the pump is running, but severe leakage occurs once the pump stops. The shaft rotation is extremely difficult – it was attempted to rotate the shaft to a position where there is no leakage or only minimal leakage, but this was not possible. I’m not sure whether it’s the mechanical seal that’s broken or something else; could you help analyze it?
Which company manufactured it? What model of pump is it, and what is the inlet pressure? What’s the temperature?
Sometimes, when the sealing surfaces of a mechanical seal have minor defects, a liquid film can be formed during rotation, so the leakage is not noticeable; however, once the machine stops, these defects become apparent. The issue you mentioned of the machine not being able to rotate may be related to internal abrasions, such as those in the balance drum or impeller collar, and repairs are necessary.
The mechanical seal definitely needs to be replaced. As for the reason, it’s necessary to find out carefully (1. Over time, the preload becomes insufficient)； 2. There are scratches on the surfaces of the stationary and rotating rings ； 3. Cavitation occurred, which caused the mechanical seal to burn out ； Wait), I’m not sure what type of multi-stage pump you have – is it suitable for pumping liquefied gas?
Blow off the mechanical seal with steam, and try turning the shaft
It is designed to transport liquefied gas, from the spherical tank to the equipment; the outlet pressure is around 2.4 Mpa. In the past, there was some leakage when the system was shut down, but once the unit was moved to a certain position, the leakage basically stopped； But this time the leakage was severe
But now the leakage is severe; all the liquefied gas inside has been drained
It is advisable to use steam to blow away the mechanical seal before turning the liquefied gas pump, in order to prevent damage to the sealing surface caused by freezing of the seal surface (low temperatures resulting from slight leakage).
1. The machine seal cover is damaged and has scratches. When the pump is running, the path of these scratches remains unchanged; however, after the pump stops running, vibrations and other factors can cause the path of the scratches to shift, leading to leaks. This phenomenon is quite common, so it is necessary to minimize the number of times the pump is started and stopped. Each start and stop puts stress on the machine seal, so the pump should not be started and stopped casually. If it’s this kind of case, the only option is to replace the casing. 2. If there is dirt on the cover, and if it’s possible to separate the cover, try cleaning the end surfaces online; this might be effective. Of course, depending on the structure of the mechanical seal, some cannot have their end faces separated.
Remove the mechanical seal and conduct a hydrostatic test to check for any leaks If pressure retention is not possible, it must be repaired or replaced.
Let’s wait until the maintenance team takes a look at it today; it probably will need to have its seal replaced