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The factors causing failures of mechanical seal, in addition to design defects,improper installation occupies a considerable proportion. It is simple to install and easy to operate cartridge mechanical seals ,during installation of which it's less likely to have problems ; while it is relatively complicated to install bulk mechanical seals . This paper takes the basic type of mechanical seals(spring type and metal bellow type) as examples to analyze and study the failure of mechanical seal caused by problems during installation.
For the mechanical seal with spring，failure of auxiliary seals of stationary seats often occur. One cause is often that auxiliary seals are damaged by burrs during installation. That is，during the installation process of the stationary seat, the auxiliary seal of the stationary seat is easily damaged by the burrs in the stationary seat flange (or stationary seat/secondary ring seat), which reduces or even loses its sealing performance completely, so that the leaking medium is sprayed around or injected from the quenching hole.Therefore, during installation, the contact part between the stationary seat flange (secondary ring seat) and the auxiliary seal should be checked first to ensure that there are no other defects such as burrs.
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For metal bellow mechanical seals，failures often are manifested in the following three forms：
1. "Swelling" of auxiliary seals
Due to the wrong lubricant used for the auxiliary seal during installation of the mechanical seal, the auxiliary seal and the lubricant have similar miscibility, and the auxiliary seal loses elasticity and then fails.For example, if ethylene-propylene rubber is used for the secondary seal and the lubricant used during installation is mineral oil, the ethylene-propylene rubber will "swell" and lose its sealing properties. Therefore, before installation of the mechanical seal, a suitable lubricant must be selected according to the material of the auxiliary seal.
2.Auxiliary seal bearing uneven screw preload
If the tightening screw is not evenly tightened, the force on the auxiliary seal will be uneven, resulting in leakage of the mechanical seal. Thus，during installation, using a torque wrench to ensure the same pre-tightening force of each screw to avoid leakage is required.
3. Welded metal bellow seals suffer from a leakage point caused by drop
During installation of the mechanical seal, attention must be taken about the seal to prevent from damages caused by accidental falling. If the welded metal bellows mechanical seal is dropped, it is prone to damages invisible to the naked eye, and there will be a leakage point, which will cause its sealing performance to fail, and this failure cannot be repaired at the site of use.
For the mechanical seal with spring，failure of auxiliary seals of stationary seats often occur. One cause is often that auxiliary seals are damaged by burrs during installation. That is，during the installation process of the stationary seat, the auxiliary seal of the stationary seat is easily damaged by the burrs in the stationary seat flange (or stationary seat/secondary ring seat), which reduces or even loses its sealing performance completely, so that the leaking medium is sprayed around or injected from the quenching hole.Therefore, during installation, the contact part between the stationary seat flange (secondary ring seat) and the auxiliary seal should be checked first to ensure that there are no other defects such as burrs.
For metal bellow mechanical seals，failures often are manifested in the following three forms：
1. "Swelling" of auxiliary seals
Due to the wrong lubricant used for the auxiliary seal during installation of the mechanical seal, the auxiliary seal and the lubricant have similar miscibility, and the auxiliary seal loses elasticity and then fails.For example, if ethylene-propylene rubber is used for the secondary seal and the lubricant used during installation is mineral oil, the ethylene-propylene rubber will "swell" and lose its sealing properties. Therefore, before installation of the mechanical seal, a suitable lubricant must be selected according to the material of the auxiliary seal.
2.Auxiliary seal bearing uneven screw preload
If the tightening screw is not evenly tightened, the force on the auxiliary seal will be uneven, resulting in leakage of the mechanical seal. Thus，during installation, using a torque wrench to ensure the same pre-tightening force of each screw to avoid leakage is required.
3. Welded metal bellow seals suffer from a leakage point caused by drop
During installation of the mechanical seal, attention must be taken about the seal to prevent from damages caused by accidental falling. If the welded metal bellows mechanical seal is dropped, it is prone to damages invisible to the naked eye, and there will be a leakage point, which will cause its sealing performance to fail, and this failure cannot be repaired at the site of use.
