Precautions for mechanical seals

Mechanical seals are also called end face seals and are mainly used to seal the rotating shafts of pumps, compressors, hydraulic drives and other similar equipment. The mechanical seal is a sealing device composed of a pair and several pairs of moving rings and static rings consisting of a plane friction pair.

The mechanical seal is a device that prevents fluid leakage by keeping at least a pair of end faces perpendicular to the axis of rotation under the action of fluid pressure and the elastic force (or magnetic force) of the compensation mechanism and the cooperation of the auxiliary seal to prevent fluid leakage. If the auxiliary seal of the compensation ring is a metal bellows, it is called a bellows mechanical seal.

Matters needing attention when installing mechanical seal

  1. Pay great attention to avoid installation deviation during installation.

1) Tightening the gland should be carried out after the coupling is aligned, the bolts should be evenly supported to prevent the end face of the gland from deflection, check each point with a feeler gauge, the error is not more than 0.05 mm;

2) Check the fitting clearance (ie concentricity) between the gland and the outer diameter of the shaft or sleeve. The circumference should be even. Use a feeler gauge to check that the tolerance of each point is not more than 0.01 mm.

  1. The compression of the spring must be carried out in accordance with the regulations, and no excessive or small phenomena are allowed, and the required error is 2.00 mm. If it is too large, the specific pressure of the end face will be increased, and the end face will be worn out. Too small will cause insufficient specific pressure and can not play a sealing role.
  2. After the moving ring is installed, the beard should be able to move flexibly on the shaft. After the moving ring is pressed to the spring, it should automatically spring back.

Matters needing attention when disassembling mechanical seal

  1. Be careful when disassembling the mechanical seal. Hand hammers and flat shovels are strictly prohibited to avoid damaging the sealing elements. A pair of wire hooks can be made, and the sealing device can be pulled out by extending into the gap of the transmission seat in the direction of self-financing. If the fouling cannot be removed, it should be cleaned and then removed;
  2. If mechanical seals are used at both ends of the pump, take care of each other during assembly and disassembly to prevent one from losing one another;
  3. For the mechanical seal that has been in operation, if the gland is loose and the seal moves, the dynamic and static ring parts must be replaced, and should not be re-tightened for continued use. Because after the movement, the original running track of the friction pair will change, and the sealing of the contact surface is easily damaged.

Normal operation and maintenance of mechanical seal

1. Preparations and precautions before starting

1) Comprehensively check the mechanical seal, whether the attachments and pipeline installation are complete, and whether they meet the technical requirements;

2) Before starting the mechanical seal, perform a static pressure test to check whether the mechanical seal is leaking. If there are too many leaks, find out the cause and try to eliminate it. If it is still invalid, it should be disassembled, checked and reinstalled. The general static pressure test pressure is 2~3 kg/cm²;

3) Rotate the pump to the crank and check whether it is light and even. If the crank is difficult or does not move, check whether the assembly size is wrong and whether the installation is reasonable.

2. Installation and shutdown

1) Keep the sealed cavity filled with liquid before starting. When transporting solidified media, steam is used to heat the sealed cavity to melt the media. The car must be cranked before starting to prevent the soft ring from being broken due to sudden start;

2) For mechanical seals that utilize the pump external oil sealing system, the oil sealing system should be activated first. Finally stop the oil sealing system after stopping;

3) After the hot oil pump is shut down, the cooling water in the oil seal cavity and end seal cannot be stopped immediately. The cooling water should be stopped when the oil temperature at the end seal drops below 80 degrees to avoid damage to the sealing parts.

3. Operation

1) If there is a slight leakage after the pump is started, it should be observed for a period of time. If the leakage does not decrease after 4 hours of continuous operation, the pump should be stopped for inspection;

2) The operating pressure of the pump should be stable, and the pressure fluctuation should not exceed 1 kg/cm²;

3) When the pump is in operation, avoid pumping out to avoid dry friction on the sealing surface and damage to the seal;

4) The sealing condition should be checked frequently. During operation, when the leakage exceeds the standard, the heavy oil should not exceed 5 drops/min, and the light oil should not exceed 10/min. If there is no improvement trend within 2-3 days, the pump plug should be stopped and the sealing device should be checked.

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