What is the common sense of mechanical seal selection-- 204 Mechanical seal

Date of issue: 2021-01-16 Author: Dongtai Guangming Mechanical Seal Co., Ltd Click:

What is the common sense of mechanical seal selection-- 204 Mechanical seal

For the selection of seals, the working conditions shall be taken into consideration, so as to select the appropriate seal form, material and installation structure.

The working conditions to be considered generally include: temperature, pressure, medium. Its mechanical seals also need to be selected according to the characteristics of the equipment itself.

As for temperature, for example, the working temperature range of NBR material is generally - 40~+120 ℃. If the temperature exceeds 120 ℃, FKM or even PTFE material will be considered. Low temperature is relatively rare. Generally, cold resistant NBR should be considered when the temperature is - 20~- 40 ℃. Generally, NBR materials in low temperature environment will lead to material hardening and leakage. For example, railway locomotives often have such problems in winter in the north.

As for pressure, it will affect the form of seal to be selected. Generally speaking, the selection of rubber or PU seal for low and medium pressure of mechanical seal will not cause too much problem. However, an impact pressure problem should be considered. For example, the impact pressure of construction machinery is much higher than the normal working pressure when it is started and closed. Therefore, impact resistance and anti extrusion clearance HBY or SPGW with pressure resistance up to 70MPA are often used as the main seal. PTFE combination seal is also a common choice.

The problem of media is relatively simple. It is only necessary to pay attention to some special small problems. For example, water glycol and phosphate hydraulic oil are often used in oil tanks in the metallurgical industry. Sometimes, although the working temperature is not high, the material selection should be very careful, and FKM should be used when using the latter hydraulic oil.

The selection of sealing elements is very important, which should be based on the situation of the equipment itself. For example, if you need to be sensitive, of course, you should choose Stefangler circle for control. High reliability is required, and Honger's GD1000K series or NOK's SPGW are often selected. For another example, the construction machinery working in the field often has impact and low temperature weather, and its dust ring will choose the exposed metal skeleton to avoid falling off.

Cylinder, compressor piston ring, high pressure oil seal and oil pump in various scientific instruments all need special structure to meet the requirements.

There are different kinds of seals. Welcome to talk with me about the selection of seals

What common sense do you have about mechanical seals?

Mechanical seal is one of the precision and complex mechanical basic elements, and it is the key component of various 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、 Selection method

According to different working conditions and medium properties, mechanical seals include high-temperature and low-temperature resistant mechanical seals, high-pressure and corrosion resistant mechanical seals, particle resistant mechanical seals, and mechanical seals suitable for light hydrocarbon media that are easy to vaporize. Mechanical seals with different structures and materials shall be selected according to different uses.

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

What is the common sense of mechanical seals? 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

Common sense of mechanical seal 1. Requirements of mechanical seal on machine precision (taking pump mechanical seal as an example)

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

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

(3) The 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.

Common sense of mechanical seal II. 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. 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 dimensions

During installation, the installation dimension of the mechanical seal shall be ensured according to the product instructions or samples.

(2) Before installation, the shaft (sleeve) and gland shall be free of burrs 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 measures such as blocking, flushing, cooling, and filtering shall 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.

The main parameters of model selection include: pressure of sealing chamber (MPa), fluid temperature (℃), working speed (m/s), fluid characteristics and effective space for installing seals.

The basic principles of model selection are:

1. According to the pressure of the sealing chamber, determine whether the sealing structure is balanced or unbalanced, single end or double end;

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

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