Mechanical seal is also known as the end face seal, which has a pair of end faces perpendicular to the axis of rotation, the end face under the action of fluid pressure and compensation mechanical external force, depending on the coordination of the auxiliary seal and the other end to keep fit, and relative slide, so as to prevent fluid leakage. Credo Pump summarizes the common leakage causes of water pump mechanical seal:

Common leakage phenomenon　

The proportion of mechanical seal leakage accounts for more than 50% of all maintenance pumps. The operation quality of mechanical seal directly affects the normal operation of the pump. It is summarized and analyzed as follows:

1. Periodic leakage

Pump rotor shaft channel momentum, auxiliary seal and large interference of the shaft, the moving ring cannot move flexibly on the shaft, when the pump is turned over, the dynamic and static ring wear, no compensation displacement.

Countermeasures: In the assembly of mechanical seal, the shaft momentum of the shaft should be less than 0.1mm, and the interference between the auxiliary seal and the shaft should be moderate. While ensuring the radial seal, the movable ring can be flexibly moved on the shaft after assembly (the movable ring can be freely bounced back to the spring).

2. Insufficient lubricating oil on the sealing surface will cause dry friction or draw the seal end face.

Countermeasures: The height of the lubricating oil surface in the oil chamber should be higher than the sealing surface of the moving and static rings.

3. Periodic vibration of the rotor. The reason is that the stator and upper and lower end covers do not balance the impeller and spindle, cavitation or bearing damage (wear), this situation will shorten the sealing life and leakage.

Countermeasures: The above problems can be corrected according to the maintenance standards.

Leakage due to pressure

1. Mechanical seal leakage caused by high pressure and pressure wave due to the excessive spring specific pressure and total specific pressure design and the pressure in the sealing chamber exceeding 3MPa, will make the specific pressure on the sealing end face too large, making it difficult for liquid film to form, serious wear on the sealing end face, increased calorific value and resulting in thermal deformation of the sealing surface.

Countermeasures: in the assembly machine seal, the spring compression must be carried out in accordance with the provisions, do not allow too large or too small phenomenon, high pressure conditions under the mechanical seal should take measures. In order to make the end face force reasonable, as far as possible to reduce the deformation, can use hard alloy, ceramics and other materials with high compressive strength, and strengthen the cooling lubrication measures, choose  transmission mode, such as key, pin, etc.

2. vacuum pump mechanical seal leakage caused by the operation in the process of starting, stopping, due to the pump inlet blockage, pumping medium containing gas, is likely to cause a negative pressure seal cavity, seal cavity if negative pressure, the dry friction causes the seals, built-in type mechanical seal will produce (water) of leak phenomenon, vacuum seal and the difference of positive pressure seal directional difference of object, and the adaptability of mechanical seal has a certain direction.

Countermeasure: adopt double end face mechanical seal, it is helpful to improve lubrication condition and seal performance.

Leakage caused by the medium

1. Most of the submersible pump mechanical seal dismantling, static ring and moving ring auxiliary seals are inelastic, some have rotted, resulting in a lot of leakage of the machine seal and even grinding shaft phenomenon. Due to high temperature, the weak acid in sewage, weak base on static ring and moving ring auxiliary rubber seal corrosion, resulting in mechanical leakag is too large, dynamic and static ring rubber seal material for nitrile -- 40, high temperature resistant, acid-alkali resistant, when the sewage is acidic and alkaline easy to corrosion.

Countermeasures: to corrosive media, rubber parts should be high temperature resistant, weak acid resistance, weak alkali fluororubber.

2. Mechanical seal leakage caused by solid particle impurities. If solid particles into the seal face, will be cut or speed up the seals of wear and tear, scale and the oil accumulation on the surface of the shaft (set), at a faster rate than wear rate of friction pair, the ring can't compensate displacement of abrasion, hard to hard friction pair work longer than hard to graphite friction pair, because of the solid particles are embedded graphite sealing ring sealing surface.

Countermeasure: The mechanical seal of tungsten carbide friction pair should be selected in the position where the solid particles are easy to enter.

Because of other problems caused by the leakage of mechanical seals mechanical seals still exist in the design, selection, installation and other unreasonable places.

1. The spring compression must be carried out in accordance with the rules, and it is not allowed to be too large or too small. The error is ±2mm.

2. The end face of shaft (or shaft sleeve) installing movable ring seal ring and the end face of seal gland (or shell) installing static ring seal ring should be chamfered and polished to avoid damage of stationary ring seal ring during assembly.