Common Sense and Application of Mechanical Seal Selection

Mechanical seal is one of the precision and complex mechanical basic elements, and is the key component of various mechanical seal pumps, reaction synthesis kettles, turbine compressors, submersible motors and other equipment. Its sealing performance and service life depend on many factors, such as model selection, machine accuracy, correct installation and use, etc.

1、 The selection method of mechanical seal is based on different working conditions and medium properties, including high-temperature and low-temperature mechanical seal, high-pressure and corrosion resistant mechanical seal, particle resistant medium mechanical seal and mechanical seal suitable for light hydrocarbon medium that is easy to vaporize. Mechanical seal with different structure types and materials shall be selected according to different uses.

The main parameters of model selection include: seal chamber pressure (MPA), fluid temperature (℃), working speed (M/S), characteristics of fluid mechanical seal and effective space for installing seal.

The basic principles of model selection are:

1。 According to the pressure of the sealing chamber, the sealing structure is determined to be balanced or unbalanced, single or double end.

2。 According to the working speed, the rotary type or static type, hydrodynamic type or non-contact type shall be adopted.

3。 According to the temperature and fluid properties, determine the friction pairs and auxiliary sealing materials, and correctly select the lubrication, flushing, insulation, cooling and other mechanical seal cycle protection systems.

4。 Multiple springs or single springs or Wave spring , internal or external.

2、 Requirements for installation and use of mechanical seal 1. Requirements of mechanical seal on machine precision (taking mechanical seal for pump as an example)

(1) The maximum radial runout tolerance of the shaft (or shaft sleeve) installed with the mechanical seal shall not exceed 0.04~0.06MM.

(2) Axial displacement of rotor shall not exceed 0.3mm.

(3) The maximum runout tolerance between the locating end face of the seal cavity and the seal end cover and the shaft (or shaft sleeve) surface shall not exceed 0.04~0.06MM.

2. Confirmation of seals

(1) Confirm whether the installed seal is consistent with the required model.

(2) Before installation, carefully compare with the general assembly drawing to see if the number of parts is complete.

(3) For mechanical seal driven by parallel coil spring, its spring can be left or right rotation, which must be selected according to the rotation direction of the shaft.

3. The installation method varies with the type of mechanical seal and the type of machine, but the installation essentials are almost the same. The installation steps and precautions are as follows: (1) When determining the installation size, the installation size of the mechanical seal should be ensured according to the product's instructions or samples.

(2) Before installation, the shaft (shaft sleeve) and gland shall be punctured and the bearing shall be in good condition; Seals, shafts, seal chambers and glands shall be cleaned. In order to reduce friction resistance, the part where mechanical seal is installed on the shaft shall be thinly coated with oil for lubrication. Considering the compatibility of rubber O-ring, soapy water can be applied if oil is not suitable. The floating static ring without anti rotation pin should not be oiled and should be installed into the gland dry.

(3) First install the stationary ring and the gland together on the shaft, taking care not to collide with the shaft, and then install the moving ring assembly. The set screws of spring seat or transmission seat shall be tightened evenly in several times. Before the gland is fixed, push the compensation ring manually for axial compression. After loosening, the compensation ring can automatically spring back without clamping stagnation, and then lock the gland bolts evenly.

4. Using

(1) When the temperature of the conveying medium is too high, too low, or contains foreign particles, which are flammable, explosive, or toxic, corresponding blocking, flushing, cooling, filtering and other measures must be taken.

(2) Before operation, turn the gear by hand, and pay attention to whether the torque is too large, whether there is friction and abnormal sound.

(3) Pay attention to the rotation direction, whether the coupling is aligned, whether the lubricating oil addition at the bearing is appropriate, and whether the piping is correct.

(4) Before operation, first open the medium and cooling water valves, check whether the gas in the sealing chamber is completely discharged to prevent leakage caused by static pressure, and then start the machine for operation.

(5) Whether the operation is normal and stable after driving, whether there is abnormal torque caused by shaft rotation, abnormal noise and overheating.