INSTALLATION AND USE OF MECHANICAL SEALS FOR PUMPS

Mechanical seals are one of the basic mechanical components with precise and complicated structure, and are the key components of various pump seals, reaction synthesis kettles, turbine compressors, submersible motors and other equipment. Its sealing performance and service life depend on many factors, such as type selection, the accuracy of machine, and correct installation and use. Today we mainly introduce the installation and use of mechanical seals for pumps.

1. General Principles for Installation and Use of Mechanical Seals

(1) To know the situation of the equipment. It is necessary to know the speed and diameter of the shaft of the equipment, the accuracy of the equipment manufacturing and the size of the sealed cavity, the service life of the equipment itself, and the role of the equipment in the production process.

(2) Estimate the medium pressure. The pressure of the sealed chamber of the pump is generally not the outlet pressure of the pump, but lower than the outlet pressure of the pump.

(3) Find out the sealing medium. Know the state of the sealing medium, whether it is gaseous or liquid, whether the medium contains particles. Know the nature and temperature of the medium, so as to reasonably select models and take necessary cooling, flushing, and lubrication measures.

2. The Requirements of Mechanical Seals on Machine Accuracy (take the mechanical seal for pump as an example)

(1) The radial operation tolerance of the shaft (or sleeve) where the mechanical seal is installed does not exceed (0.04 ~ 0.06mm).

(2) The axial movement of the rotor does not exceed 0.3 mm.

(3) The run-out tolerance of the positioning end of the sealing cavity combined with the sealing end cap on the surface of the shaft (or sleeve) does not exceed 0.04-0.06mm.

3. Confirmation of Seals

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

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

(3) A mechanical seal driven by parallel coil springs is used. The springs are divided into left and right, which must be selected according to the rotation direction of the shaft. This kind of mechanical seals is the spring seal. Certainly, it also can refer to the elastomer bellow seal.

4. Installation of Mechanical Seals

The installation method varies with the type of mechanical seals and the type of machine, but the installation method is almost the same. The installation steps and precautions are as follows:

(1) Determining the installation size. When installing, the installation size of the mechanical seal should be ensured according to the instruction manual or sample of the product.

(2) Before installing, the shaft (sleeve) and the gland should be free of burrs, and the bearings should be in good condition. The seals, shaft, seal cavity, and gland should be cleaned. In order to reduce friction resistance, a thin layer of oil should be applied to the part where the mechanical seal is installed. Considering the compatibility of the rubber 0-ring, if oil is not suitable, soapy water can be applied. The floating static ring has no anti-rotation pin structure and should not be oiled.

(3) First install the static ring and gland on the shaft, taking care not to touch the shaft, and then install the moving ring assembly. The fixing screw of the spring seat or transmission seat should be tightened evenly in several times. Before fixing the gland, 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.

5. Use of Mechanical Seals

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

(2) Before operation, use a handcart, pay attention to whether the torque is too large, whether there is friction or abnormal sound.

(3) Pay attention to the direction of rotation, whether the coupling is centered, whether the addition of lubricating oil 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 sealed chamber is completely discharged to prevent leakage caused by static pressure, and then start the operation.

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