The mechanical seal gradually recovers after leaking
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Phenomenon: In a three-screw oil transfer pump, leakage was detected in the mechanical seal; the leakage rate was around 50 drops per minute. At that time, the pressure was 2.0 MPa and the flow rate was 440 m3/h. No measures were taken for encrypted inspections. As the operating conditions changed, the pressure gradually increased to 2.5 MPa, the displacement was around 480, and the leakage rate increased to about 80 drops per minute. As the operating conditions continued to change, the pressure gradually dropped to 2.0 MPa, the displacement was around 500, and the leakage rate decreased to about 2 drops per minute. During these approximately 12 hours from the detection of the leak to the end, the viscosity of the medium increased, but the temperature also rose. Please help analyze: What is the condition of this mechanical seal, and is it necessary to replace it immediately? Thank you
This post was last edited by 3983596_FPPZ on 2018-11-22 at 17:55. First of all, the flow rate of this screw pump is really high. Based on the leakage situation, it seems that the wear of the sealing surfaces or some issue with the static seals is causing the leakage; it’s not due to a break in the rotating or stationary rings. Therefore, I believe that no sudden leakage will occur if the pump continues to be used, but regular inspections at the site are necessary. Personally, I recommend that to ensure safe operation, shutting down the equipment for disassembly, inspection, and repair is the best approach; continuing to operate it despite its faults is not a good idea.
If there is a spare unit, the pump can be switched over for inspection. We encounter this situation quite often as well: after operating for a while, the sealing surfaces fit together properly and then everything is fine, or the leakage stops once the spring is adjusted during operation. Sometimes, upon disassembly, it turns out that the mechanical seal is actually in good condition. Let’s keep observing going forward
What do you mean by the viscosity increasing as the temperature increases? Has the medium changed? What is a medium? I’ve really never seen a screw pump with a capacity of 450 liters
In cases like this where the natural conditions are favorable, considering that changes in load affect the fit of the sealing surfaces, it would be advisable to stop the pump for maintenance if possible, and have the manufacturer check the PV values and the springs as well.
Personally, I think recovery is just a coincidence. It’s better to get it checked as soon as possible to be sure. [Personal opinion for reference only]
Sorry, let me correct that: two pumps operate in parallel, at their rated discharge rates – one with a capacity of 400 m3 and the other at 350 m3. Both are driven by frequency converters.
The medium remains unchanged; it’s still crude oil. It can also be said that it has changed; at first, more light oil was used, while later less light oil was added
Thank you. Although there is a backup pump, we are basically unable to conduct inspections after it stops working. The sealed installation is quite deep, and there are no inspection tools or methods available. Generally, disassembly is quite complicated; considering cost-effectiveness, it’s usually necessary to replace it with a new one when taken apart.
Thank you, this question has been bothering me. Sometimes, upon disassembly, coking is observed on the sealed bellows, which is suspected to be the main cause of the leakage. The removed sealing surface showed virtually no leakage in tests. Due to the high cost of disassembly, we generally replace it with a new one as soon as it needs to be disassembled.
There’s no need to replace it; just add a 2-mm gasket in front of the mechanical seal.