The main reasons for the failure of mechanical seals in slurry pumps

The failure of mechanical seals in slurry pumps mainly has the following three causes: The sealing surface is opened. When repairing mechanical seals, 85% of seal failures are not caused by wear but by leakage before wear occurs. When the sealing surface is opened, solid particles in the medium enter the sealing surface under the action of liquid pressure. After the sealing surface closes, these solid particles are embedded in the surface of the soft ring (usually the right rubber ring), which actually becomes a "grinding wheel" and damages the surface of the hard ring. Because the dynamic ring or rubber ring is tightly fastened to the shaft (shaft sleeve), when the shaft moves, the dynamic ring cannot adhere in time, thus opening the sealing surface. And the delayed closure of the sealing surface allows solid particles to enter the sealing surface. At the same time, there are also solid particles between the shaft (shaft sleeve) and the sliding parts, which affect the sliding of the rubber ring or the moving ring (common faults at the relative dynamic sealing point). In addition, the medium may also form crystalline substances at the friction area between the rubber ring and the shaft (shaft sleeve), and solid substances may also be present at the spring, all of which can cause the sealing surface to open. (2) Overheating Due to the heat generated on the sealing surface, the operating temperature of the rubber ring should be lower than the design specification. The operating temperatures of fluororubber and polytetrafluoroethylene are 216℃, and that of nitrile rubber is 162℃. Although they can all withstand relatively high temperatures, the heat generated on the sealing surface is high, so there is a risk of further vulcanization of the rubber ring, eventually losing its elasticity and causing leakage. (Cold areas should consider cold brittleness.) Between the sealing surfaces, the medium may crystallize due to heat, such as carbonization, causing the sliding parts to be stuck and the sealing surfaces to be condensed. Moreover, some polymers may caramelize due to overheating, and some fluids may lose their lubrication or even flash due to overheating. Overheating not only changes the state of the medium but also accelerates its corrosion rate. It causes deformation of metal parts, cracking of alloy surfaces, and cracking of certain coatings. The design should select a balanced mechanical seal to reduce the specific pressure and prevent overheating. (3) Beyond tolerance limits The correct assembly tolerance is very necessary for installing mechanical seals. The shaft (shaft sleeve) must have the appropriate surface roughness and correct dimensions. However, manufacturers rarely provide tolerance data, which are all very crucial for installation. The dimensional accuracy and positional tolerance of mechanical seals must comply with the requirements of the drawings. Any deviation beyond the tolerance will lead to premature failure of the seal.