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Common sense and use of mechanical seal selection

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

1、 Selection method

According to different working conditions and medium properties, mechanical seals are high temperature and low temperature resistant, high pressure and corrosion resistant, granular medium resistant and light hydrocarbon medium suitable for vaporization. Mechanical seals of different structural types and materials shall be selected according to different uses.

The main parameters of model selection are: pressure of seal cavity (MPA), fluid temperature (℃), working speed (M / s), characteristics of fluid mechanical seal and effective space for seal installation.

The basic principles of model selection are:

1. According to the pressure of the seal cavity, it is determined that the seal structure adopts the balanced type or non balanced type, single end face or double end face, etc.

2. According to the working speed, 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, as well as the correct selection of lubrication, flushing, heat preservation, cooling and other mechanical seal circulation protection system.

4. According to the effective space of installation seal, it is determined to adopt multiple springs or single springs or wave springs, internal or external.

2、 Installation and use requirements of mechanical seal

1. Requirements of mechanical seal for machine accuracy (take mechanical seal for pump as an example)

(1) The maximum radial runout tolerance of the shaft (or sleeve) installed at the mechanical seal shall not exceed 0.04-0.06mm.

(2) The 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 sleeve) surface shall not exceed 0.04-0.06mm.

2. Seal confirmation

(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) The mechanical seal driven by the parallel spring has left and right rotations, which must be selected according to the rotation direction of the 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) When determining the installation dimension, the installation dimension of the mechanical seal shall be ensured according to the product instruction or sample.

(2) Before installation, the shaft (shaft sleeve) and gland shall be pricked and the bearing shall be in good condition; the seal, shaft, sealing cavity and gland shall be cleaned. In order to reduce the friction resistance, a thin layer of oil shall be applied to the parts where the mechanical seal is installed on the shaft for lubrication. Considering the compatibility of the rubber O-ring, if it is not suitable to use oil, soapy water can be applied. Floating static ring without anti rotation pin is not suitable for oiling, and should be installed into gland dry.

(3) First, install the static ring and gland on the shaft, taking care not to collide with the shaft, and then install the dynamic ring assembly. The set screw of spring seat or drive seat shall be tightened evenly in several times. Before the gland is not fixed, push the compensating ring by hand for axial compression. After loosening, the compensating ring can automatically spring back without jamming, and then lock the gland bolt evenly.

4. Use

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

(2) Before operation, use hand turning gear, and pay attention to whether the torque is too large, whether there is any scratch and abnormal sound.

(3) Pay attention to the direction of rotation, whether the coupling is aligned, 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 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, as well as abnormal noise and overheating.