204 Mechanical seal Causes of infiltration

（1） Leakage due to pressure

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

Cause: The design of spring specific pressure and total specific pressure is too large. When the pressure in the sealing chamber exceeds 3MPa, the specific pressure of the sealing face will be too large, and the liquid film will be difficult to form. The sealing face will be severely worn, and the heat generation will increase, resulting in thermal deformation of the sealing face.

Solution: When assembling the mechanical seal, the spring compression must be carried out according to the regulations. It is not allowed to be too large or too small. Measures should be taken for the mechanical seal under high pressure. In order to make the end face stress reasonable and minimize deformation, materials with high compressive strength such as cemented carbide and ceramics can be used, and cooling lubrication measures can be strengthened.

2. Fault 2: mechanical seal leakage caused by vacuum operation

Causes: During the starting and stopping of the pump, the seal chamber may have negative pressure due to the blockage of the pump inlet and the gas contained in the pumped medium. If the seal chamber has negative pressure, it will cause dry friction of the seal end face, and the built-in mechanical seal will have air (water) leakage.

Solution: Double end mechanical seal is adopted for assembly, which helps to improve lubrication conditions and sealing performance.

（2） Leakage caused by medium

1. Fault 1: The auxiliary seals of the stationary ring and the moving ring are inelastic or some have rotted, resulting in a large amount of leakage of the mechanical seal and even grinding of the shaft.

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 rubber seals of the dynamic and static rings are made of 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.

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

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

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

Solution: The mechanical seal of tungsten carbide to tungsten carbide friction pair shall be selected at the position where solid particles are easy to enter.