Mechanical seals and spring hangers come in various models, but there are five primary leakage points:
1. The seal between the sleeve and the shaft
2. The seal between the rotating ring and the sleeve
3. The seal between the rotating and stationary rings
4. The seal between the stationary ring and its seat
5. The seal between the end cover and the pump housing
**Leakage During Static Testing**
After installing and adjusting a mechanical seal, a static test is typically conducted using a basket filter to observe the leakage amount. If the leakage is minimal, it may indicate an issue with the sealing of the rotating or stationary ring. A significant leak suggests a problem with the friction pair between the rotating and stationary rings. By observing the leakage pattern manually, you can determine the source: if the leakage remains constant, the issue is likely with the seal; if it changes during cranking, the friction pair may be faulty. If the medium sprays axially, the rotating ring seal is probably at fault. If it sprays outward or leaks through the cooling hole, the stationary ring seal is likely compromised. Multiple leaks can occur simultaneously, but one is usually dominant. With careful observation and a good understanding of the structure, accurate diagnosis is possible.
**Leakage During Commissioning**
Once the static test is complete, the centrifugal force from high-speed rotation helps prevent leakage. Therefore, any leakage during operation is generally due to failure in the friction pair after the initial seal has failed. Common causes include:
- Abnormal conditions like cavitation or surge causing excessive axial force that separates the rings
- Excessive compression during installation leading to severe wear
- Too tight a seal on the rotating ring, preventing proper axial movement
- A loose seal on the stationary ring, causing it to separate during movement
- Solid particles entering the friction faces during operation
- Incorrect design selection, such as low pressure resistance or poor material compatibility
These issues often appear during trial runs and may require adjustment or reassembly to resolve.
**Failure Due to Loss of Lubricating Film**
- Dry friction occurs when the seal chamber lacks liquid upon startup
- The medium may flash due to vapor pressure, breaking the lubricating film
- Volatile media can cause pressure increases from friction and stirring, reducing lubrication
**Failure Due to Corrosion**
- Pitting or penetration of the sealing surfaces
- Intergranular corrosion in stainless steel seats welded to tungsten carbide rings
- Cracking in metal bellows or springs under stress and corrosive conditions
**Failure Due to High Temperatures**
- Thermal cracking is common in high-temperature pumps, especially oil slurry or refinery pumps
- Graphite rings can carbonize beyond their temperature limits, leading to softening and leakage
- Elastomer seals can age, crack, or harden at high temperatures, reducing effectiveness
**Failure Due to Wear on the Seal Faces**
- Poor wear resistance of friction pair materials leads to shorter service life
- Solid particles entering the seal face act as abrasives, accelerating wear
- The balance ratio (β) affects wear; 75% is ideal, while 80–85% is better for high-temperature media
**Leakage Due to Installation, Operation, or Equipment Errors**
- Improper installation can damage the rings, misalign seals, or create gaps
- Axial vibration, unstable operation, or pressure fluctuations cause periodic leakage
- Incorrect material selection, spring misalignment, or excessive vibration can all lead to failure
- After shutdown, solidification, scaling, or corrosion may occur, affecting performance
- Shaft misalignment can also cause repeated leaks
At Hebei Qingyu Pipeline Equipment Manufacturing Co., Ltd., we specialize in providing reliable mechanical sealing solutions. Our products are designed to meet the highest standards of performance and durability. For more information, visit [www.chinawj.com.cn](http://www.chinawj.com.cn).
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