Reasons and solutions for leakage of mechanical seal manufacturers

Date of issue: 2022-04-10 Author: Dongtai Guangming Mechanical Seal Co., Ltd Click:

Mechanical seal manufacturer Causes of liquid leakage and solutions

Mechanical seal refers to a device composed of at least one pair of end faces perpendicular to the rotation axis, under the action of fluid pressure and the elastic force (or magnetic force) of the compensation organization, and with the cooperation of the auxiliary seal, to maintain sticking and relative sliding, thus preventing fluid leakage.

Introduce the reason of mechanical seal leakage and the treatment method of water pump leakage:

Whether it is self-priming pumps, centrifugal pumps, QW submersible sewage pumps and other mechanical seals are the key reasons for the leakage of industrial water pumps.

Mechanical seal is also called end face seal. It has a pair of end faces perpendicular to the rotation axis. Under the effect of fluid pressure and external elastic force of compensation machinery, the end faces rely on the cooperation of auxiliary seals to maintain contact with the other end and slide relatively, so as to prevent fluid leakage.

01 Common leakage

The proportion of mechanical seal leakage accounts for more than 50% of all industrial water pump leakage. The operation of mechanical seal directly affects the normal operation of water pump. The summary and analysis are as follows:

02 Reasons for incentive penetration

（1） Leakage due to pressure

1. Obstacle I: mechanical seal leakage caused by high pressure and pressure wave

Cause: The specific pressure of the spring and the total specific pressure are designed to be too large. When the pressure in the sealing chamber exceeds 3MPa, the specific pressure of the sealing face will be too large, which will make it difficult to form the liquid film. The wear of the sealing face is important, and the amount of heat will increase, forming the thermal deformation of the sealing face.

Treatment method: when the mechanical seal is equipped, the spring shrinkage must be carried out according to the regulations. It is not allowed to be too large or too small. The mechanical seal under high pressure should adopt countermeasures. In order to make the end face stress correct and reduce deformation, materials with high compressive strength such as cemented carbide and ceramics can be selected, and the smooth countermeasures of cooling can be strengthened.

2. Obstacle II: mechanical seal leakage caused by vacuum operation

Cause: In the process of starting and stopping the pump, as the pump inlet is congested and the pumped medium contains gas, negative pressure may appear in the seal chamber. If the negative pressure in the seal chamber is not allowed, it will lead to dry conflict of the seal end face and air (water) leakage of the built-in mechanical seal.

Treatment method: double end mechanical seal is used to improve the smooth condition and improve the sealing function.

（2） Leakage caused by medium

1. Obstacle 1: The auxiliary seals of the stationary ring and the moving ring are inelastic, and some of them may still be rotting, resulting in a large amount of leakage of the mechanical seal and even shaft grinding.

Cause: High temperature and weak acid and alkali in sewage corrode the static ring and auxiliary rubber seals of the dynamic ring, resulting in excessive mechanical leakage. The raw material of the dynamic and static ring rubber seals is nitrile 40, which is not resistant to high temperature and acid and alkali. When the sewage is acidic and alkaline, it is easy to corrode.

Treatment method: For corrosive media, the rubber parts shall be fluororubber with high temperature resistance, weak acid resistance and weak alkali resistance.

2. Obstacle II: mechanical seal leakage caused by vacuum solid particle impurities

Cause: When solid particles enter the sealing end face, they will scratch or accelerate the wear of the sealing end face. The stacking speed of scale and oil stains on the shaft (sleeve) surface exceeds the wear speed of the collision pair, so that the moving ring cannot compensate for the wear displacement. The operating life of the hard to hard collision pair is longer than that of the hard to graphite collision pair, because solid particles will be embedded in the sealing surface of the graphite sealing ring.

Treatment method: mechanical seal of tungsten carbide to tungsten carbide conflict pair shall be selected at the position where solid particles can easily enter.

Mechanical seal leakage caused by other problems

There are still some problems in the design, selection and installation of mechanical seals.

(1) The spring shrinkage must be carried out according to the regulations. It is not allowed to be too large or too small. The deviation is ± 2mm. If the shrinkage is too large, the end face specific pressure will be increased. If the conflict heat is too much, the thermal deformation of the sealing face will be formed and the end face wear will be accelerated. If the shrinkage is too small, the end face specific pressure of the dynamic and static rings will be insufficient, and the sealing will not be allowed.

(2) The end face of the shaft (or shaft sleeve) for installing the dynamic ring seal ring and the end face of the sealing gland (or housing) for installing the static ring seal ring shall be chamfered and polished to avoid damaging the dynamic and static ring seal ring when it is equipped.

Mechanical seal itself is a sophisticated part with high requirements for design, machining and equipment quality. When using mechanical seals, various factors of using mechanical seals should be analyzed, so that the technology of applying mechanical seals to various pumps should address the requirements of using media and have sufficient smooth conditions, so as to ensure the long-term and reliable operation of seals.