Causes and Countermeasures of Mechanical Seal Failure in Reducer

Writer：tilireducer Time：2026-07-30 16:05:47 Browse：6℃

 Leakage is one of the common malfunctions of mechanical equipment.

There are primarily two reasons for the leakage:

Firstly, due to the results of mechanical processing, various defects, shape deviations, and dimensional deviations inevitably exist on the surface of mechanical products. Therefore, gaps will inevitably occur at the joints of mechanical parts;

Secondly, if there is a pressure difference between the two sealed sides, the working medium will leak through the gap.

Reducing or eliminating gaps is the primary way to prevent leakage. The function of a seal is to seal the gap between mating surfaces, isolate or cut off the leakage path, increase the resistance in the leakage path, or add small working components in the path to apply pressure on the leakage material, which can partially offset or completely balance the pressure difference causing the leakage, thereby preventing leakage. 37% of reducer failures are due to mechanical seal failures, 31% are due to bearing failures, and 32% are due to other reasons.

1. Principle and requirements of mechanical seals

Mechanical seals, also known as face seals, are shaft sealing devices for rotating machinery. They consist of at least one pair of end faces perpendicular to the axis of rotation, which, under the combined action of liquid pressure, the elastic force (or magnetic force) of the compensation mechanism, and the cooperation of auxiliary seals, remain in contact and slide relative to each other, thus preventing fluid leakage.

Its main function is to change the easily leaking axial seal into a less prone to leakage end face seal.

It is widely used for sealing the rotating shafts of pumps, kettles, compressors, and other similar equipment. Reduction gearboxes are generally divided into two types: single-stage transmission and multi-stage transmission. Regardless of the type of reduction gearbox, the internal structural components are composed of shafts, bearings, gears, couplings, casings, and other related parts.

A mechanical seal is typically composed of a rotating ring, a stationary ring, a clamping component, and a sealing component. The rotating ring rotates along with the pump shaft, and the rotating ring and the stationary ring closely fit together to form a sealing surface, preventing medium leakage. The rotating ring is pressed against the end face of the stationary ring by the pressure of the liquid in the sealing chamber, creating an appropriate specific pressure on the end faces of the two rings and maintaining a very thin liquid film to achieve sealing. The clamping component generates pressure, allowing the pump to maintain end face fit even when not in operation, ensuring that the sealing medium does not leak and preventing impurities from entering the sealing end face. The sealing component seals the gap between the rotating ring and the shaft, as well as the gap between the stationary ring and the gland. At the same time, the elastic component provides cushioning against pump vibration and impact. In actual operation, the mechanical seal operates in combination with other pump components. The normal operation of the mechanical seal is closely related to its own performance and external conditions. However, we must first ensure the performance of our own components, auxiliary sealing devices, and installation technical requirements to allow the mechanical seal to perform its intended function.

II. Fault Manifestations and Causes of Mechanical Seals

1. Failure of mechanical seal components

During the operation of rotating equipment, the sealing end face often experiences wear, thermal cracking, deformation, and damage. The spring, after prolonged use, may also become loose, break, and corrode. The auxiliary sealing ring may also exhibit cracks, twisting, deformation, and breakage.

2. Causes of vibration and heating faults in mechanical seals

During the rotation of the equipment, the mating end face of the rotating and stationary rings may become rough, and the gap between the rings and the sealing chamber may become too small. This can lead to vibration caused by collisions due to runout. Sometimes, poor corrosion resistance and temperature resistance of the sealing end face, insufficient cooling, or the presence of particulate impurities on the end face during installation can also cause vibration and heating of the mechanical seal.

3. Fault causes of mechanical seal medium leakage

3.1 - Leakage during static pressure test

During the installation of mechanical seals, carelessness often leads to damage, deformation, or breakage of the sealing end face. If the cleaning is not thorough, or if there are granular impurities trapped, or if the positioning screws are loose, the gland is not tightened, or the precision of the machinery and equipment is insufficient, resulting in incomplete sealing of the sealing surface, medium leakage can occur. If the leakage is from the shaft sleeve, it is due to the shaft sleeve seal ring not being compressed tightly during assembly, insufficient compression, or damage.

3.2 - Periodic or intermittent leakage

Periodic vibration and excessive axial play of the rotor assembly in a mechanical seal can cause leakage. The sealing surface of a mechanical seal must have a certain specific pressure to perform its sealing function, which requires a certain amount of compression in the spring of the mechanical seal to provide a thrust to the sealing end face, rotating it to generate the specific pressure required for sealing. To ensure this specific pressure, the mechanical seal requires that the pump shaft not have excessive play, generally within 0.25mm. However, in practical design, due to improper design, the pump shaft often experiences significant play, which is very detrimental to the use of the mechanical seal.

3.3 - Frequent leakage of mechanical seals

There are many reasons for the frequent leakage of mechanical seals.

The first aspect is the frequent leakage caused by defects in the sealing end face.

The second aspect concerns the frequent leakage caused by the auxiliary sealing ring.

The third aspect concerns leakage caused by defects in the spring.

In other aspects, leakage can also be caused by rotor vibration, poor quality or looseness of transmission, fastening, and thrust components, leakage due to mechanical seal auxiliary mechanisms, and frequent leakage caused by issues with the medium.

3.4 - The vibration of the mechanical seal is relatively high

The vibration of the mechanical seal is relatively large, ultimately leading to the loss of sealing effect. However, the reasons for the relatively large vibration of the mechanical seal are often not solely attributed to the mechanical seal itself. Other components of the pump are also the root causes of vibration, such as unreasonable design of the pump shaft, processing reasons, insufficient bearing accuracy, poor parallelism of the coupling, and large radial forces.

III. Measures taken to handle faults

If the components of the mechanical seal fail, it is necessary to replace the parts or enhance the machining precision of the components. Improving the machining precision of both the mechanical seal itself and other components of the pump body is highly beneficial to the effectiveness of the mechanical seal. To enhance the sealing effect, there are stringent requirements for the smoothness and unevenness of the friction surfaces of the rotating and stationary rings. The width of the friction surfaces of the rotating and stationary rings is not large, generally ranging from 2 to 7 millimeters.

1. Handling of vibration and heating of mechanical seals

If the clearance between the rotating and stationary rings and the sealing chamber is too small, it is necessary to increase the inner diameter of the sealing chamber or reduce the outer diameter of the rotating part, ensuring a minimum clearance of 0.75mm. If the friction pair is mismatched, the materials of the rotating and stationary rings should be changed to make them temperature-resistant and corrosion-resistant. This will reduce the vibration and heat generation of the mechanical seal.

2. Handling of mechanical seal leakage

Leakage of mechanical seals can be caused by various reasons, and we need to address specific issues in a specific manner. To minimize the leakage, the mechanical seal must be installed strictly in accordance with technical requirements, and the following points should also be noted.

2.1 - The assembly should be clean and smooth

The components, tools, lubricants, and wiping materials for mechanical seals must be exceptionally clean. The sealing surfaces of the rotating and stationary rings should be wiped with soft gauze.

2.2 - Chamfering and rounding

The chamfer of the shaft, sealing end cap, etc. should be trimmed smooth, and the relevant fillets of the shaft and end cap should be sanded and polished.

2.3 When assembling the auxiliary sealing ring, the rubber auxiliary sealing ring should not be soaked or washed with gasoline or kerosene to avoid swelling, deformation, and premature aging. After the assembly of the rotating and stationary rings, manually press the compensation ring to check whether it is in place and flexible, and whether the elastic split ring is reliably positioned. After the installation of the rotating ring, it must be ensured that it can move flexibly in the axial direction on the shaft.

3. Handling of large axial play in pump shaft

Reasonably design the axial force balancing device to eliminate axial play. To meet this requirement, for multi-stage centrifugal pumps, the design scheme is: a balancing disc plus an axial thrust bearing, where the balancing disc balances the axial force and the axial thrust bearing provides axial restraint for the pump shaft.

4. Add an auxiliary flushing system

The sealing medium in the sealing chamber contains particles and impurities, which must be flushed out. Otherwise, the spring of the mechanical seal may fail due to the precipitation of crystals and the deposition of particles and impurities. If particles enter the friction pair, it will lead to the rapid destruction of the mechanical seal. Therefore, the auxiliary flushing system of the mechanical seal is very important. It can effectively protect the sealing surface, play a role in cooling, lubricating, and flushing away impurities.

After briefly examining the application and malfunctions of mechanical seals on rotating equipment, when encountering mechanical seal failures in the future, we should first consider the influencing factors of the mechanical seal itself, and then consider some external influencing factors of the mechanical seal. For example, when analyzing the causes of mechanical seal quality accidents, we should consider the impact of other pump components on the operation of the mechanical seal, and take measures to continuously improve the effectiveness of the mechanical seal.

With the advancements in materials and manufacturing technology, the reliability of mechanical seals has been greatly enhanced, and now mechanical seals themselves can operate without failure for many years. There are not many cases where the leakage of the reducer is solely due to the mechanical seal itself. When addressing the issue of reducer leakage, we must comprehensively consider factors such as the installation accuracy of the reducer, operating conditions, and the assembly accuracy of the mechanical seal, identify the cause, and solve the existing problems in a targeted manner.