Mechanical seal faults are generally caused by abnormal changes caused by leakage, wear, torque, etc., resulting in machine seal failure mainly due to the following three points:

1, design selection is wrong;

2, the installation factors or the characteristics of the pump itself;

3, seal failure.

The specific circumstances also need specific analysis, the following mainly about the reasons for the failure of the seal analysis, the first two points of this understanding may be more clear than we know, but the seal of the machine seal failure little known, the main seal failure as follows point:

First, the sealing surface open

When repairing a mechanical seal, most of the seal failure is not caused by wear, but rather leaks prior to wear. When the sealing surface is opened, the solid particles in the medium enter the sealing surface under the action of liquid pressure. After the sealing surface is closed, the solid particles are embedded in the surface of the soft ring (usually graphite ring), which effectively becomes a similar "grinding wheel "Can damage hard surfaces.

As the moving ring or rubber ring fastened to the shaft (sleeve), when the shaft drive, the ring can not fit in time, leaving the sealing surface open, and the sealing surface of the hysteresis closed, the solid particles into the sealing surface. At the same time there are also solid particles between the shaft (sleeve) and the sliding parts, affecting the sliding of the rubber ring or moving ring (relative to the dynamic sealing point, common faults). In addition, the media will also produce friction between the rubber ring and the shaft (sleeve) to produce crystalline material, there will be a solid material in the spring, will open the sealing surface.

Second, the temperature is too high

Because the sealing surface will produce heat, so the actual use of rubber ring temperature is usually lower than the marked temperature. Fluorine rubber and PTFE use temperature of 216 ℃, nitrile rubber temperature of 162 ℃, although they are able to withstand higher temperatures, but the heat generated by the sealing surface is high, so the rubber ring has continued vulcanization Danger, eventually losing its elasticity and leakage. Sealing surfaces can also cause crystallization of the medium due to heat, such as carbon formation, causing the sliding parts to stick and the sealing surface to be coagulated. And some polymer due to overheating and coking, some fluids due to overheating and even lost lubrication and other flash fire. In addition to overheating can change the condition of the medium, but also exacerbated its corrosion rate, causing deformation of metal parts, alloy surface cracking, and some plating cracks, the design should be balanced mechanical seal to reduce the pressure to prevent compression Too much caused by excess heat can not be ruled out in time caused by high temperature.

Third, the seal itself

For poor quality graphite ring (moving ring), the internal pores more, because in the manufacturing process, the accumulation of gas inside the graphite expansion of carbon particles due to the blow, so this low-quality graphite ring In the opening of the seal, the carbon particles are easy to fall off, leaving the sealing surface to stick when the seal is deactivated. Normally, overheating of the hard ring (stationary ring) surface can cause wear on the seal ring's eyes, such as vertical pumps without cooling. In high temperature, high pressure, the spring compression is too large, the shaft drive will be too large, will cause the sealing surface excessive wear and tear.

Pay special attention to the following four phenomena on the surface of the stationary ring: Broken ceramic rings, heat, nicks, peeling off of the coating.

Fourth, the abnormal situation

1, the pump sleeve leakage: sleeve leakage is usually stable, while the sealing surface leakage is often increased or decreased. Leakage of sealing surface, the surface uneven, but sometimes also run into the original state. (Sometimes do not rush to overhaul, can be observed for some time to say).

2, micro-osmosis: If the bees are wet around, but do not see the leak, which pump at the start of the centrifugal force generated by the rotation of the leaked liquid back to the sealing surface, play a barrier role. The pump flange or connector leakage of liquid dripping into the stuffing box.

3, thermal expansion: thermal expansion can be set in the metal parts of the graphite ring loose, it may be due to the low temperature O-ring loses its elasticity, leading to leakage.

In short, for the seal failure, try to find out why the customer convinced, so as to win the trust of customers.