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The main reason for the failure of the mechanical seal of the slurry pump

2021-11-19
The main reason for the failure of the mechanical seal of the slurry pump

There are three main reasons for the failure of the mechanical seal of the slurry pump:

(1) The sealing surface is open

When repairing mechanical seals, 85% of seal failures are not caused by wear, but have leaked before wear.

When the sealing surface is opened, the solid particles in the medium enter the sealing surface under the action of the liquid pressure. After the sealing surface is closed, these solid particles are embedded in the surface of the soft ring (usually the right ink ring), which actually becomes a " The “grinding wheel” will damage the surface of the hard ring.

Since the moving ring or rubber ring is fastened to the shaft (sleeve), when the shaft is moved in series, the moving ring cannot be attached in time, which causes the sealing surface to open, and the sealing surface is closed with a hysteresis, so that solid particles enter the sealing surface .

At the same time, there are solid particles between the shaft (sleeve) and the sliding parts, which affect the sliding of the rubber ring or the moving ring (relative to the dynamic seal point, common failure). In addition, the medium will also produce crystals at the friction between the rubber ring and the shaft (sleeve), and there will also be solid substances in the spring, which will cause the sealing surface to open.

(2) Overheating

Since heat is generated on the sealing surface, the operating temperature of the rubber ring should be lower than the design specification. The service temperature of fluorine rubber and polytetrafluoroethylene is 216℃, and the service temperature of nitrile rubber is 162℃. Although they can withstand higher temperatures, the heat generated by the sealing surface is higher, so the rubber ring continues to vulcanize The danger of eventually losing its elasticity and leaking. (Consider cold brittleness in cold zone)

The heat between the sealing surfaces will also cause the crystallization of the medium, such as carbon formation, causing the sliding parts to be stuck and the sealing surface to be condensed. Moreover, some polymers are coked due to overheating, and some fluids lose lubrication due to overheating, and even flash fire.

In addition to changing the condition of the medium, overheating can also increase its corrosion rate. Cause the deformation of metal parts, cracks on the alloy surface, and some cracks in the coating, the design should select a balanced mechanical seal to reduce the specific pressure to prevent overheating.

(3) Out of tolerance

The correct assembly tolerances are necessary for the installation of mechanical seals. The shaft (sleeve) must have the proper surface roughness and the correct size, but the manufacturer rarely provides tolerance data, which is critical for installation. of.

The dimensional accuracy and form and position tolerances of mechanical seals must meet the requirements of the drawings. Excessive tolerance will lead to premature seal failure.