Type Selection Method of Mechanical Seals

According to the different working conditions and medium properties, mechanical seals have high temperature and low temperature resistance, high pressure and corrosion resistance, granular medium resistance and light hydrocarbon medium adaptable to vaporization. Different structural types and materials should be selected according to different uses.

The main parameters of type selection are: pressure of sealing chamber (MPa), temperature of fluid (C), working speed (m/s), characteristics of fluid and effective space for installation of sealing, etc.

The basic principles of type selection are as follows:

1. According to the pressure of the sealing chamber, the seal structure is determined to be balanced or non-balanced, single-end or double-end.

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

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

4. According to the effective space of the installation seal, the multi-spring or single-spring or waveform spring, internal or external type are adopted.

II. Installation and Use Requirements of Mechanical Seals

1. Requirements of Mechanical Seals for Machine Accuracy (Take Mechanical Seals for Pumps as an Example)

(1) The maximum radial run-out tolerance of the shaft (or sleeve) installed with mechanical seals does not exceed 0.04-0.06mm.

(2) The axial movement of the rotor is not more than 0.3 mm.

(3) The maximum run-out tolerance of the positioning end face of the shaft (or sleeve) surface combined with the sealing cavity and the sealing end cover is not more than 0.04-0.06mm.

2. Confirmation of Seals

(1) Verify that the installed seal is in conformity with the required type.

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

(3) Mechanical seals driven by parallel coil springs, whose springs are divided into left and right rotation, should be selected according to the rotation direction of the shaft.

3. Installation of mechanical seals

Installation methods vary according to mechanical seal type and machine type, but the installation essentials are almost the same. Installation steps and precautions are as follows:

(1) Determination of Installation Size

Installation, according to the product instructions or samples, to ensure the installation size of mechanical seals.

(2) Before loading, the shaft (sleeve) and pressure cap should be burr-free and the bearing is in good condition. Seals, shafts, sealing chambers and pressure caps should be cleaned. In order to reduce friction resistance, mechanical seals installed on the shaft should be thinly coated with oil to lubricate. Considering the compatibility of rubber O-rings, soap water can be applied if oil is not suitable. Floating static ring without anti-reselling structure, not suitable for oil, should be dry loaded into the cap.

(3) Firstly, the static ring and the cover are mounted on the axle together, and then the moving ring assembly is mounted. The fastening screw of spring seat or transmission seat should be tightened evenly several times.

Before the cap is not fixed, the manual compensation ring is used as the axial compression. After loosening, the compensation ring can automatically bounce back without sticking phenomenon, and then the cap bolt is locked evenly.

4. Use of mechanical seals

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

(2) Use the handwheel before running, pay attention to whether the torque is too large, whether there are scratches and abnormal sounds.

(3) Pay attention to the direction of rotation, whether the coupling is aligned, whether the lubricant addition at the bearing position is appropriate, and whether the piping is correct.

(4) Before operation, the medium and cooling water valves should be opened to check whether all the gases in the sealing chamber are discharged to prevent leakage caused by static pressure, and then start operation.

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