1.      Mechanical seals which is also called end face seal, it has a pair of perpendicular to the axis of the rotating end face, the face in the fluid pressure and compensation under the action of mechanical stretch, rely on the auxiliary seal, keep fit with the other end, and the relative sliding, thus preventing fluid leakage.
A periodic common, leakage
1) The pump rotor axial momentum large, secondary seal and shaft interference quantity is big, ring cannot be flexible on the shaft to move.Turn on the pump, dynamic and static ring wear, without compensation displacement.
Countermeasures: when in the assembly of mechanical seal, shaft axial momentum should be less than 0.1 mm, moderate amount of interference, auxiliary seal on the shaft in the guarantee of radial seal at the same time, can guarantee on the shaft collar is assembled flexible mobile (freedom of press ring to the spring can bounce back)
2) Sealing surface lubricating oil quantity insufficient cause dry friction or hair the seals
Countermeasures: the oil level of lubrication in oil cavity height should be higher than the dynamic and static ring sealing surface
3) Pperiodic vibration, rotor, the reason is the stator and the upper and lower cover not on or in the impeller and shaft imbalance, cavitation or bearing damage
2.       The leakage due to pressure
1) High pressure and the pressure wave caused by the leakage of mechanical seal
Due to the large spring than pressure and total pressure design, the pressure inside the sealed cavity more than 3 mpa, can make the seal face specific pressure is too large, difficult to form, liquid membrane seal face serious wear and tear, calorific value increase, sealing surface caused by the thermal deformation.
Countermeasures: in the assembly of mechanical seal, the amount of compression spring must be in accordance with the provisions of, don't allow too big or too small.Measures should be taken to mechanical seal under the condition of high pressure, and to make the end force is reasonable, can use hard alloy, high crushing strength of the material such as ceramic, and strengthen the lubrication cooling measures.
2) The mechanical seal leakage, vacuum operation
Pump in the process of up, stop, due to the pump inlet blockage, pumping medium containing gas, is likely to cause a negative pressure seal cavity, resulting in seal face dry friction.
Countermeasures: adopt double mechanical seal, it helps improve the lubrication conditions, improve the sealing performance.
3.       Caused by medium leakage
Medium particles, impurities into the sealing face, and make the seal failure;Dynamic and static ring auxiliary seal, weak acid, weak alkali corrosion due to the medium loss due function.
Countermeasures: ensure the purity of the lower cover, oil chamber, do not clean the oil ban assembly;Mechanical seal oil cavity oil line should be higher than the sealing face;According to the different media with different structure of the mechanical seal, such as the corrosive medium, rubber parts should choose high temperature resistant, resistant to weak acid, weak base of fluorine rubber, the solid particles is easy to enter the location of the selection of tungsten carbide tungsten carbide mechanical seal friction pair.
Four, mechanical seal leakage caused by other problems
Mechanical seal is unreasonable design, selection, installation, etc
Countermeasures: amount of spring compression error should be between 2 mm - 2 mm, is raises the face specific pressure, friction heat is overmuch, easy cause and accelerate the end face sealing surface thermal deformation wear, too small, dynamic and static ring end face specific pressure is insufficient, can't seal;Installation of gland ring sealing ring (or shell) should end chamfering and light, to avoid bruising dynamic and static ring sealing ring when assembly.
Above summarizes the mechanical seal leakage of common causes and countermeasures.Mechanical seal itself is a kind of requirement of high precision components.When use, should analysis of various factors, make suitable for all kinds of pump mechanical seal technology demands and use the medium, so as to ensure long-term reliable operation.