Mechanical seals, as the core sealing component of power and fluid equipment, are directly related to the operational safety of the equipment and the stability of production. In the conveying equipment of the chemical, pharmaceutical, food and other industries, even rotor pumps—a type of positive-displacement pump with relatively high sealing requirements—frequently suffer from problems such as medium leakage and shutdown for maintenance caused by seal failure, posing considerable challenges to production continuity.

-Bonve Pumps Cam-Type Twin-Rotor Pump-

 I. Core Causes of Leakage

· Seal Failure Caused by Corrosion

Corrosion is a common cause of mechanical seal failure, mainly manifested at three levels. If the metal ring itself has insufficient corrosion resistance, its surface will be gradually eroded after coming into direct contact with corrosive media, accompanied in the early stage by abnormal noise, seepage and abnormal wear, and the corrosion will continue to spread along the interior of the material. Under the action of stress, the metal ring becomes deformed, and the exposed parts become the hardest-hit areas of corrosion, ultimately spreading along the weak links and leading to seal failure.

As for the non-metallic ring, the corrosion of the graphite ring must not be ignored either. Excessively high end-face temperature, deviation in the selection of the impregnating resin, or insufficient impregnation depth will all accelerate the deterioration of the graphite ring. When the graphite ring is in an oxidizing medium environment, once cooling is inadequate or friction intensifies, the end-face temperature can reach three to four hundred degrees, prompting an oxidation reaction between the graphite and the medium, and the performance of the sealing face declines significantly as a result.

Auxiliary seal rings are mostly made of elastic rubber; after being corroded, their surfaces become rough and their elasticity is lost. Moreover, the upper temperature limit of rubber usually does not exceed 200°C, and under high-temperature working conditions the aging speed is noticeably accelerated. At the stationary parts in contact with the seal ring, gap accumulation and fretting friction will also induce corrosion, and the corroded surface is often both wide and deep.

· Fault Manifestations Under Different Working Conditions

Seepage occurring during the hydrostatic test stage is mostly related to installation quality. Bumping and deformation of the sealing end face, residual particle impurities, loosening of the positioning screws, an untightened gland, or insufficient equipment precision can all cause the sealing face to fit imperfectly. If the leakage point is located at the shaft sleeve, it may be that the compression amount of the shaft sleeve seal ring is insufficient, the assembly is not in place, or the component is already damaged.

Periodic seepage is usually related to the rotational pattern of the rotor assembly and an excessive axial float of the pump shaft. The sealing face needs to maintain an appropriate specific pressure in order to work effectively, which relies on the preload force provided by the spring. If the control of axial displacement is insufficient during the design stage and the float of the pump shaft exceeds the permissible range, the fitting state of the sealing face will fluctuate periodically, forming regular leakage.

Frequent leakage mostly originates from damage to the sealing end face. Common forms include uniform annular grooves on the graphite end face, annular deep grooves, inner-edge wear, flattened steps, outer-edge notches, ring-body fracture, and corrosion pits, as well as cracks and thermal scorching appearing on the hard-alloy face. Aging of the auxiliary seal ring, loosening of the inlaid ring, spring fatigue, and abnormal rotor vibration will also cause continuous seepage.

In addition, working conditions such as cavitation in the seal chamber, end-face vaporization, excessive pump-body vibration, the absence of a flushing system, or the pump running dry may all induce seal leakage.

 II. Targeted Treatment and Prevention Measures

Installing an interlock protection device is an effective means of preventing serious accidents. For example, an electric-contact pressure gauge can be set at the pump outlet, establishing an interlock between the pump operation and the outlet pressure, so that once the pressure drops sharply the power supply is automatically cut off. To prevent the medium from flowing back and causing reverse rotation when the pump is stopped, a check valve can be installed on the outlet pipeline.

In terms of structural optimization, the double-face seal has a large contact area with the medium, so the corrosion risk is relatively higher. On the premise of meeting safety requirements, a single-face bellows mechanical seal structure can be adopted instead, reducing the medium contact area while improving the compensation capability.

In terms of material selection, the corrosion-resistance grade should be matched according to the characteristics of the medium. Ceramic materials are chemically stable and not prone to reacting with the medium, so ceramic seal rings can be given priority in corrosive working conditions; for graphite rings, attention must be paid to the compatibility between the impregnation process and the type of resin.

At the operational level, standardizing work procedures and personnel training are of vital importance. Human operating errors are an important cause of early seal failure. By preparing standardized work instructions, introducing fool-proof (poka-yoke) designs, and regularly carrying out skill training, the seal damage caused by human factors can be significantly reduced.

In terms of maintenance and overhaul, it is necessary to change the situation in which routine inspections are conducted merely as a formality. Most seal faults have early warning signs, and meticulous inspection can detect problems at the budding stage. Enterprises can put in place corresponding incentive mechanisms to guide maintenance personnel to pay attention to details and improve the actual effectiveness of daily maintenance.

Mechanical seal leakage is often the result of multiple superimposed factors—from process conditions, equipment status and overhaul quality to operating standards, a deviation in any single link may lead to failure. Only through systematic investigation and multi-dimensional prevention and control can the leakage risk be truly reduced and the long-term stable operation of the machine pump be guaranteed.

Bonve pump always adheres to the philosophy of "Wholeheartedly Making Good Rotor Pumps," committed to providing global customers with customized conveying and mixing solutions. If you have technical inquiries, selection needs, case references, or other cooperation intentions related to Bonve rotor pumps, please feel free to contact us.  

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Official Website: www.bvpumps.com  

Business Email: market@bonvepumps.com  

We look forward to working with you to drive efficiency and innovation in industrial fluid transmission with precision technology.