FAULT ANALYSIS OF MECHANICAL SEAL

The working principle of mechanical seals is a pair or pairs of sliding ends arranged vertically with the shaft. Due to the pull of pressure from moving objects and elastic force of compensating mechanism, the mechanical seals are tightly connected with other ends with the help of auxiliary seals while keeping relative motion between each other and finally avoiding fluid leakage. In addition to mechanical seals, common seals are spring seals, pump seals, gland packings, non contacting mechanical seals, and elastomer bellow seals. The following contents mainly introduce the failure causes of mechanical seals and their solutions.

Specific Causes of Mechanical Seal Failure

Deficiencies in the mechanical seal itself can lead to mechanical seal failure, such as improper installation, improper selection of sealing materials, too flat sealing surface and too wide or too small sealing surface.

Problems and deficiencies in auxiliary systems may lead to mechanical seal failure, such as cumbersome working conditions, lack of special flushing equipment, blocked flushing pipe and dirt in cooling pipe.

Defects in the media and working environment can lead to mechanical seal failure, e.g. the medium is too corrosive, the medium is doped with solid material, the sealing surface crystallizes and the medium is too viscous.

Defects in the pump can lead to mechanical seal failure, e.g. poor shaft accuracy, excessive vibration during operation of the pump, uneven surface of the seal box, and the mechanical seal does not meet the specific compression requirement standard during installation.

Problems and Solutions of Pump and Mechanical Seal in Operation

Problem: The axial movement of pump rotor is large, the interference between auxiliary seal and shaft is large, and the moving ring can not move flexibly on shaft. The compensated displacement is not available after the pump is rotated and the moving and static rings are worn.

Solution: When assembling the mechanical seal, the axial displacement of the shaft shall be less than 0.1mm, and the interference between the auxiliary seal and the shaft shall be moderate. While ensuring the radial seal, the moving ring shall be able to move flexibly on the shaft after assembly.

Problem: Due to the high temperature, the weak acid and alkali in the sewage corrode the auxiliary rubber seal of the moving ring and the static ring, resulting in the excessive mechanical leakage. The material of the rubber seal ring of the moving ring and the static ring is nitrile-40, which is not resistant to high temperature and acid and alkali. When the sewage is acid or alkaline, it is easy to be corroded.

Solution: If the medium is corrosive, the rubber parts of the pipeline shall be made of fluororubber with high temperature resistance, weak acid resistance and weak alkali resistance. Too much compression of the spring will increase the specific pressure and friction heat of the end face, which will cause thermal deformation of the sealing surface and accelerate the wear of the end face. Too small compression of the spring will cause insufficient specific pressure on the end face of the moving and static rings, which can not achieve the sealing effect.