Mechanical seal failure issue (single-spring type)
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In my workshop, there is an important centrifugal hot water pump; its working medium is desalinated water, with a flow rate of 1840, a temperature of 168 degrees, a rotational speed of 1480, and an inlet pressure of 1.9 Mpa. There was a period of time when mechanical seal leaks occurred frequently; the lifespan of these seals was such that leaks in the form of a stream of fluid appeared after about 30 days of use. After disassembly, inspection shows that the stationary and rotating rings are in good condition with no damage ； The auxiliary sealing O-ring is undamaged and in good condition ； The main sealing surface is undamaged, but contains a small amount of contaminants ； Process adjustments were made before the leakage occurred, resulting in some pressure fluctuations. I’d like to ask everyone about the problem. I hope everyone can give more suggestions
Should desalinated water not be very pure? Where do the impurities come from? Is the pressure fluctuating frequently or does it stabilize at a certain value after adjustment? If it keeps fluctuating, the seal might be damaged due to vibration; but if no damage is found upon actual inspection, it’s hard to say for sure. Take a look at the selection of the seal
Seal leakage should not be caused by impurities; what is the sealing solution? Process parameters of the auxiliary system? This is very crucial; the sealing materials are now up to standard, and the focus lies in the sealing solution.
If it’s leaking everywhere as you said, with everything else in good condition, could it be that the spring is too small? You might consider increasing the spring specific pressure a bit to see
Based on what the poster has said, the reasons seem to be: 1. Large pressure fluctuations, which can likely lead to vacuum conditions and thus cause sealing leaks; this is probably the main reason； 2. Additionally, there are impurities in the deionized water, which may be caused by corrosion in the pipelines of the standby equipment.
The most important thing is to determine the range of pressure fluctuations in order to identify the cause.
In my opinion: it’s likely that the nut of the fixed shaft sleeve is loose, causing a leak at the static point
Our factory also had such pumps! Firstly, its design may have a flaw: the pressure applied to the mechanical seal is too high, which causes water to be forced out through the seal between the rotating and stationary rings. The maximum pressure exerted on the stationary and rotating rings of a standard mechanical seal is usually 2.1 MPa. Most pumps are designed with pressure-reduction mechanisms; however, your pump may not have such a mechanism, which means the mechanical seal is subjected to a pressure of 1.9 MPa. Over time, as the compressive force of the seal’s springs decreases slightly, water will start to leak out. If the pump is not replaced, the only option is to increase the pressure of the seal spring; this will also shorten the lifespan of the seal, though it will be better than the situation you described above. If the spring force is adjusted properly, it should last about 3 months! That's it!
If impurities can get through the sealing surface, then leakage is only a matter of time; it seems there’s a problem with the spring
Pay attention to the solutions later. A pressure of 1.9 MPa is a bit high; the elasticity of large springs may not be uniform, so try using smaller springs. Anyway, it’s now standardized, so it’s easy to replace.
1.9 Using a large spring does indeed result in uneven stress distribution; since the leakage occurs in the form of a stream of fluid, it’s definitely a problem with the mechanical seal surface. Another factor is the quality of your desalinated water; I’ve seen this happen often as well – impurities have a significant impact on seals.