Mechanical seal selection requirements

Mechanical seals are one of the basic mechanical components with precision and complex structure, 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.u200bu200b

First, the selection method:

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

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 medium-resistant mechanical seals and mechanical seals suitable for easily vaporized light hydrocarbon media.

Seals, etc., mechanical seals with different structural types and materials should be selected according to different uses.u200bu200b

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 type, fluid dynamic pressure type or non-contact type.

3: According to the temperature and fluid properties, determine the friction pair and auxiliary sealing materials, and correctly select the lubrication, flushing, heat preservation, cooling and other mechanical seal circulation protection systems.u200bu200b

4: According to the effective space of the installation seal, determine the use of multiple springs or single springs or wave springs, built-in or external.u200bu200b

Second, the installation and use requirements of mechanical seals:

1: Requirement of mechanical seal on machine precision (take mechanical seal for pump as an example)

(1) The maximum radial runout tolerance of the shaft (or shaft sleeve) where the mechanical seal is installed should not exceed 0:04～0:06MM.u200bu200b

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

(3) The maximum runout tolerance of the positioning end of the sealing cavity and the sealing end cover facing the surface of the shaft (or shaft sleeve) does not exceed 0:04~0:06MM.u200bu200b

2: Confirmation of seals

(1) Confirm whether the installed seal is the same as the required model.

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

(3) For the mechanical seal driven by the parallel coil spring, the spring can be divided into left and right rotation, which must be selected according to the rotation direction of the rotating shaft.u200bu200b

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's instruction manual or sample.

(2) Before loading, the shaft (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 the 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, be careful not to touch 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.u200bu200b

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 filtering 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 lubrication oil in the bearing is properly added, and whether the piping is correct.

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

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