1、 Method for selecting mechanical 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 resistant mechanical seals, and mechanical seals suitable for light hydrocarbon media that are prone to vaporization. Different structural types and materials of mechanical seals should be selected according to their different uses.

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

The basic principles for selection are:

1. Determine whether the sealing structure adopts balanced or unbalanced type, single end face or double end face, etc. based on the pressure of the sealing chamber.

2. Determine whether to use rotary or static, fluid dynamic or non-contact type based on the working speed.

3. Determine the friction pair and auxiliary sealing materials based on temperature and fluid properties, as well as correctly select mechanical seal circulation protection systems such as lubrication, flushing, insulation, and cooling.

4. Determine whether to use multi spring, single spring, or wave spring, internal or external, based on the effective space for installing the seal.

2、 Installation and usage requirements for mechanical seals

1. Requirements for machine accuracy for mechanical seals (taking pump mechanical seals as an example)

(1) The maximum radial runout tolerance of the shaft (or sleeve) for installing mechanical seals shall not exceed 0.04-0.06mm.

(2) The axial displacement of the rotor shall not exceed 0.3mm.

(3) The maximum runout tolerance of the positioning end face of the sealed cavity combined with the sealed end cover to the surface of the shaft (or shaft sleeve) shall not exceed 0.04-0.06mm.

2. Confirmation of seals

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

(2) Before installation, carefully compare with the final assembly drawing to ensure that the number of parts is complete.

(3) The mechanical seal using parallel coil spring transmission has left and right rotation springs, which must be selected according to the rotation direction of the shaft.

3. Installation of mechanical seals

The installation method varies depending on 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 dimensions of the mechanical seal should be ensured according to the product's user manual or sample.

(2) Before installation, the shaft (sleeve) and cover should be free of burrs, and the bearing condition should be good; Seals, shafts, sealing chambers, and glands should all be cleaned thoroughly. To reduce frictional resistance, a thin layer of oil should be applied to the parts where mechanical seals are installed on the shaft for lubrication. Considering the compatibility of rubber O-rings, if oil is not suitable, soap water can be applied. Floating static rings without anti rotation pins should not be coated with oil and should be installed in a dry manner under the cover

(3) First, install the static ring and the cover on the shaft together, being careful not to touch the shaft, and then install the dynamic ring assembly. The fastening screws of the spring seat or transmission seat should be tightened evenly in several times.

Before fixing the cover, manually push the compensating ring for axial compression. After loosening, the compensating ring can automatically rebound without any jamming phenomenon, and then evenly lock the cover bolts.

4. Use of mechanical seals

(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 sealing, flushing, cooling, and filtering must be taken.

(2) Before operation, turn the car by hand and pay attention to whether the torque is too high, whether there are any scratches or abnormal sounds.

(3) Pay attention to the rotation direction, whether the coupling is aligned, whether the lubricating oil addition at the bearing part is appropriate, and whether the piping is correct.

(4) Before operation, first open the medium and cooling water valves, check if all the gas in the sealed chamber is discharged to prevent leakage caused by static pressure, and then start the machine for operation.

(5) Whether the work is normal and stable after driving, whether there are any abnormal torques caused by shaft rotation, abnormal noises, and overheating phenomena.