What is the method for adjusting the compression amount of a double-faced mechanical seal?
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This post was last edited by zhangya*ong on 2009-9-24 at 15:12. Double-end mechanical seals are mostly modular seals, meaning that a single seal unit contains two pairs of friction pairs. The double-face mechanical seals used in our factory typically last for up to two years, with an average lifespan of around one year. After one year, most of these seals start to leak under various conditions; sometimes it’s the first seal that leaks, and other times it’s the second seal. In the case of the first seal, the pressure of the medium is higher than that in the sealing tank, so any leakage will contaminate the lubricating oil in the tank. When the second seal leaks, it comes into direct contact with the atmosphere, posing a risk to the equipment. Recently, during maintenance, we found an issue with the compression amount of the double-end face mechanical seal – either the compression was too high or too low. This problem was present already at the time of manufacture. Please share your opinions: if, instead of following the original design, the shaft sleeve mounting area is machined away and the sealing compression is adjusted to 60% of the total compression amount through precise measurements, could this increase the product’s service life? Share your views – replies will be rewarded!
I wonder how the original poster determined that there was a problem with the compression amount of the mechanical seal? Aren’t their positions fixed at the time of manufacture?
The last edit to this post was made by cairenzeng on 2009-9-22 at 22:31. The compression amount for double-face cartridge mechanical seals is set by the manufacturer; theoretically, the single compression amount is half of the total compression amount, with around 5 MM being the optimal value
1. If it’s truly the case that “the double-face mechanical seals used in our factory last at most two years, with half of their useful life being around one year,” then that’s quite impressive. 2. I’m not sure what criteria the original poster is using to determine that there are issues with the compression amount of double-face mechanical seals, namely that the compression amount may be either too high or too low 3. There are various reasons for the failure of mechanical seals, resulting in \"leaks under different conditions.\" Different targeted measures should be taken to address various faults. Before correctly diagnosing the seal failure, \"adjusting the compression amount of the seal to 60 percent of the total compression amount\" – could this be a good way to extend the service life of the seal? The way the problem is approached is a bit casual and simplistic; it’s too “lazy”.
Yeah, the guy on the 4th floor is right; machine seals are vulnerable components that are often included in the annual spare parts list. If they can last around 2 years before needing to be replaced, why not be satisfied with that? ? ?
For double-faced mechanical seals with multiple springs, the compression amount of the springs is smaller; typically, such mechanical seals have a compression amount of just a few millimeters； For single-spring, single-face mechanical seals, the compression amount is relatively larger. In general, as a key principle, after the mechanical seal is installed, the spring should not be compressed too tightly, as this can cause the sealing friction pairs of the mechanical seal to be damaged and lead to leakage, provided that the shaft seal remains leak-free.
It’s indeed good if a mechanical seal can last for two years. The issues related to excessive or insufficient compression are likely related to the pressure difference; it’s best not to make any changes to it. However, what the original poster said about the medium pressure being higher than that in the sealing tank is completely wrong – if that were the case, the first seal would have failed long ago
No, it’s possible. For example, that is generally the case with the sealing fluid in a tandem double-end face seal structure. The seal fluid pressure is lower than the pressure of the medium in the preceding sealing chamber; the seal used in the preceding stage is of the internal-flow type, designed to withstand external pressure. Since the seal fluid pressure is lower than that of the medium in the preceding sealing chamber, this seal fluid functions as a buffer fluid rather than a sealing fluid, similar to the concepts of buffer gas and sealing gas in dry gas seals.
Regarding the issue raised by the original poster, I have two points to say: 1) Under normal circumstances, the pressure in the seal tank of the mechanical seal should be higher than the pressure of the medium inside. Conversely, it is entirely normal for the first sealing surface of the mechanical seal to be forced open, resulting in the seal fluid contaminating the medium or the seal fluid being contaminated by the medium! If this condition is detected during inspections of the machine seals in our factory, the operators will be held accountable. 2) The issue of insufficient compression amount of the mechanical seal mentioned by the poster. For double-end face mechanical seals, the compression amount is basically already calculated by the manufacturer during design, and it is very difficult for users to adjust it. If you are certain that it is a problem with the compression amount of the mechanical seal, you may consider contacting the manufacturer to make improvements or switching to springs with better elastic properties. If adjustments are made without proper consideration, the compression amount might be set too high, preventing a liquid film from forming on the sealing surfaces of the mechanical seal; this leads to dry friction and thus no sealing effect. Although the lubricant chosen by the manufacturer for use with this mechanical seal has a high viscosity, which facilitates the formation of a liquid film.
Haha, it seems that too many people still don’t have a sufficient understanding of mechanical seals! Any mechanical seal is adjustable, and adjustment is a fundamental method for equipment maintenance! Not knowing how to adjust is the scariest thing. Designing double-end face mechanical seals is a complement to single-end face seals; a compression ratio of 60–70% for the mechanical seal yields the best sealing performance and lifespan ； The prerequisite for making adjustments is accurate measurement; it is easier to perform measurements on single-seal systems. There are several types of double-seal systems in addition to the series configuration, and measurement and adjustment are carried out in stages. Changing the positioning of the shaft sleeve means changing the compression amount of both mechanical seals at the same time, and this approach is generally not used.
I completely agree with the first point mentioned by floor 9! The compression amount of the double-end face seal is definitely adjustable. My method of measurement is to first measure the total compression of the two sets of seals, and then measure the compression of the outer set; this way, I can determine whether the compression levels of the two sets of seals are appropriate ； There are also cases of adjustments being necessary; in the situations I’ve encountered, it was a multi-spring seal where the compression amount on each side wasn’t adjusted properly – one side had more compression than the other, which ended up crushing the springs. Before making any adjustments, we will contact the manufacturer, but processing the steps on the shaft sleeve is probably the last step to take, right?