Causes and solutions for common mechanical seal failures in multistage pumps

As the core component of the shaft end seal of a multistage pump, the frequent failure of mechanical seals not only leads to media leakage and production interruption, but also increases the cost of parts replacement and maintenance. Based on thousands of field troubleshooting experiences, HNYB PUMPS has summarized a complete solution for multistage pump mechanical seals, encompassing "precise selection, standardized installation, optimized operating conditions, and closed-loop operation and maintenance," to fundamentally extend the service life of mechanical seals and reduce the probability of failure.

 

 

• Reasons for frequent mechanical seal failure in multistage pumps

1. Excessive pump start-up and shutdown puts the mechanical seal under stress, potentially damaging it.
2. Overfeeding, exceeding the pump's design parameters, leads to excessive pressure, putting stress on the mechanical seal and causing damage.
3. Insufficient axial or radial clearance results in excessively high internal pressure, putting stress on the mechanical seal and damaging it.
4. Excessively high or low ambient temperatures cause the mechanical seal material to expand and contract due to temperature differences, leading to seal failure.
5. Improper selection of the mechanical seal, use of materials with poor wear resistance, and imprecise manufacturing processes can all contribute to quality problems with the mechanical seal.

 

• Solutions to mechanical seal failure in multistage pumps

 

Precise Selection: Avoiding the Risk of "Inherent Mismatch" from the Source

Incorrect selection is the primary cause of mechanical seal failure. HNYB PUMPS recommends precise matching based on the "three elements of operating conditions," rejecting generic applications:
**Media Characteristics Adaptation:** For conveying media containing particles (particle size > 5μm), select a mechanical seal with a silicon carbide/silicon nitride hard-on-hard sealing surface and an internal filter structure to enhance wear and erosion resistance; for highly corrosive media (acids, alkalis, salt solutions), use 316L stainless steel + PTFE composite material seals to avoid swelling and cracking; for high-temperature media (>120℃), prioritize metal bellows mechanical seals to improve thermal stability.
**Operating Parameter Matching:** Select the seal based on the actual working pressure and speed of the multi-stage pump. The rated seal pressure should be 0.3~0.5MPa higher than the pump outlet pressure, and the rated speed should not be less than 1.2 times the actual pump shaft speed; for high-pressure conditions (>10MPa), use a balanced mechanical seal to reduce sealing surface pressure.
Special Operating Conditions: For applications with frequent start-stop cycles and large pressure fluctuations, select spring-type seals with strong elastic compensation capabilities. For outdoor and humid environments, choose sealing components with an IP65 protection rating or higher to prevent moisture intrusion and damage to the internal structure.

 

Standardized Installation: Eliminating Human-Induced Damage and Building a Solid Sealing Foundation.

Improper installation accounts for over 30% of seal failures. HNYB PUMPS specifies the following core operating standards:

Pre-Installation Preparation: Thoroughly clean the sealing cavity and shaft sleeve surface, removing oil, iron filings, burrs, and other impurities. Wipe the sealing surface with a clean, soft cloth; never scrape with hard objects. Inspect the appearance of the seal components, ensuring the rotating and stationary rings are free of cracks and scratches, and the spring is free of deformation and rust.

Precision Control Points: The coaxiality error between the pump shaft and the sealing cavity should be ≤0.05mm, and the perpendicularity deviation of the sealing end face should be ≤0.02mm to avoid uneven wear during operation. The compression of the sealing spring should be strictly adjusted according to the manufacturer's requirements (usually 3~5mm). Excessive tightness can lead to overheating and wear of the sealing surface, while insufficient tightness will prevent effective sealing.

Installation and Operation Specifications: Apply appropriate media or special grease to the dynamic and static rings during installation to reduce assembly friction; tighten the gland bolts evenly to ensure the gland and shaft sleeve are coaxial and without misalignment; manually rotate the pump shaft after installation to ensure smooth rotation without jamming.

 

Operating Condition Optimization: Improve the operating environment and reduce seal loss.

Harsh operating conditions are a significant factor accelerating mechanical seal failure and require targeted optimization and adjustments: Media purification: Install a multi-stage filtration system before the pump, combining coarse and fine filtration to ensure media particle size ≤5μm; for media containing fibers, add an additional fiber filter, regularly cleaning and replacing the filter element to prevent impurities from entering the sealing surface and forming "abrasives".

Operating Condition Stability Control: Install a pressure regulating valve and a thermostat to prevent pump inlet and outlet pressure fluctuations >0.5MPa and sudden temperature changes >30℃; when conveying poorly lubricating media (such as clean water), use a seal flushing system, with flushing water pressure 0.1~0.2MPa higher than the pump cavity pressure and flow rate controlled at 0.5~1.5L/min, continuously cooling and cleaning the sealing surface. Avoid Abnormal Operating Conditions: Dry running of the pump for more than 3 minutes is strictly prohibited, as it will cause dry friction and burnout of the sealing surface. Control pump shaft axial movement to ≤0.3mm and vibration value to ≤4.5mm/s. If these limits are exceeded, promptly inspect bearings, impellers, and other components.

 

Closed-Loop Operation and Maintenance: Establish a full-cycle maintenance system to proactively prevent failures.

Scientific operation and maintenance management can significantly extend the life of mechanical seals. HNYB PUMPS recommends the following maintenance plan: Daily Inspection Focus: Monitor the sealing cavity temperature daily (normally ≤80℃). If the temperature rises sharply by more than 15℃, stop the machine for inspection. Observe the leakage rate; during normal operation, the leakage rate should be ≤5 drops/minute. If it exceeds this limit, adjust the gland or replace the seal promptly.

Regular Maintenance Plan: Under normal operating conditions, check the seal wear every 3-6 months; under harsh operating conditions (including particles, corrosion, and high temperatures), shorten this to 1-2 months; replace the mechanical seal completely annually to avoid aging and failure.

Flushing System Maintenance: Regularly clean the flushing pipeline to ensure it is free of blockages; check the flushing water quality to prevent impurities from entering the sealing cavity; close the flushing water valve when shutting down, and open it 5 minutes before restarting to ensure pre-cooling and lubrication of the sealing surface.

 

Parts Guarantee: Use Original Equipment Manufacturer (OEM) Parts to Ensure Consistent Quality

Parts quality is crucial for the long-term operation of the seal. HNYB PUMPS reminds you: Prioritize using OEM mechanical seals. Their materials and precision are perfectly matched to the pump body, and their sealing surface fit, spring elasticity, and other indicators have undergone rigorous testing, extending their service life by 2-3 times compared to non-OEM parts.

Avoid mixing sealing components of different brands and models. Differences in the dimensions of the dynamic ring, stationary ring, and springs from different manufacturers can easily lead to poor sealing surface fit, uneven pressure, and failure.

Keep OEM spare seals in stock for quick replacement in case of failure, reducing downtime; spare parts must be stored properly to avoid moisture and oil contamination, ensuring the sealing surface remains intact.

 

In summary, multistage pump mechanical seals are crucial for ensuring the efficient and safe operation of pumps. Proper use and scientific maintenance are key to preventing frequent damage to the mechanical seals. These methods can effectively improve the reliability and service life of the mechanical seals, reduce the risk of fluid leakage, and thus enhance the overall system's operating efficiency and economy.