Mechanical seal selection requirements1

Mechanical seals are one of the most precise and complex mechanical basic components, and are the key components of various pumps, reaction synthesis kettles, turbo 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. Selection method:

The main parameters of mechanical seal selection: seal cavity pressure (MPA), fluid temperature (°C), working speed (M/S), fluid characteristics and effective space for installing seals.

According to the different working conditions and the properties of the medium, the mechanical seal includes high temperature resistance, low temperature resistance mechanical seal, high pressure resistance, corrosion resistance mechanical seal, particle medium resistance mechanical seal and mechanical seal suitable for light hydrocarbon medium which is easy to vaporize.

Mechanical seals with different structural types and materials should be selected according to different uses.​​

The basic principles of selection are:

1: According to the pressure of the sealing cavity, determine whether the sealing structure is balanced or unbalanced, single-end or double-end, etc.

2: According to the working speed, determine whether to use rotary or static, hydrodynamic or non-contact.

3: According to the temperature and fluid properties, determine the friction pair and auxiliary sealing materials, and correctly select the mechanical seal circulation protection system such as lubrication, flushing, heat preservation, cooling, etc.​​

4: According to the effective space of the installation seal, it is determined to use multiple springs or single springs or wave springs, built-in or external.​​

Second, the installation and use requirements of mechanical seals:

1: The requirements of the mechanical seal on the machine precision (take the pump mechanical seal as an example)

(1) The maximum radial runout tolerance of the shaft (or shaft sleeve) where the mechanical seal is installed shall not exceed 0:04~0:06MM.​​

(2) The axial movement of the rotor does not exceed 0:3MM.

(3) The runout tolerance of the positioning end of the sealing cavity combined with the sealing end cover facing the surface of the shaft (or shaft sleeve) should not exceed 0:04~0:06MM at most.​​

2: Confirmation of seals

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

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

(3) For mechanical seals driven by parallel coil springs, the springs are divided into left and right rotations, which must be selected according to the rotation direction of the rotating shaft.​​

3: Installation

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) Determination of installation size During installation, the installation size of the mechanical seal should be guaranteed according to the product instruction manual or sample.

(2) Before loading, the shaft (sleeve) and gland should be free of burrs, and the bearing should be in good condition; the seals, shaft, sealing cavity and gland should be cleaned.

In order to reduce frictional resistance, the part where the mechanical seal is installed on the shaft should be coated with a thin layer of oil for lubrication. Considering the compatibility of rubber O-rings, if oil is not suitable, soapy water can be applied.

The structure of floating static ring without anti-rotation pin should not be oiled, and should be installed in the gland dry.

(3) Install the static ring together with the gland on the shaft first, being careful not to collide with the shaft, and then install the moving ring assembly. The set screw of the spring seat or transmission seat should be evenly tightened several times.

Before the gland is not fixed, push the compensation ring by hand for axial compression. After loosening, the compensation ring can automatically spring back without jamming, and then the gland bolts are evenly locked.​​

4: use

(1) When the temperature of the conveying medium is too high, too low, or contains impurity particles, flammable, explosive or toxic, corresponding measures such as blocking, flushing, cooling, and filtration must be taken.

(2) Turn the car by hand before running, pay attention to whether the torque is too large, whether there is friction and abnormal sound.

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

(4) Whether the work is normal and stable after driving, whether there is abnormal torque caused by the rotation of the shaft, as well as abnormal noise and overheating.

(5) Before operation, first open the medium and cooling water valves, check whether the gas in the sealed chamber is fully discharged, and prevent leakage caused by static pressure, and then start the operation.