Troubleshooting of mechanical seal of water pump
Mechanical seal is also called end face seal. It relies on the pressure of spring and sealing medium to produce appropriate pressing force on the contact surface of rotating moving ring and stationary ring to make the two end faces closely fit. An extremely thin oil film is maintained between the end faces, and the medium has great resistance when passing through, so as to prevent liquid leakage, so as to achieve the purpose of sealing, and lubricate the moving ring and static ring at the same time. If adjusted well, there can be no leakage at all.
1 Characteristics of mechanical seal of water pump
The main advantage of mechanical seal of water pump is reliable seal, with little leakage in a long service cycle; Long service life, generally about 5 years; Long maintenance cycle. However, the mechanical seal has complex structure, high manufacturing and installation accuracy, high cost and high technical requirements for maintenance personnel. Because the mechanical seals used on oil pipelines are built-in, the oil pump is often disassembled when repairing the mechanical seal, resulting in heavy workload. Therefore, it is very important to ensure the reliability of mechanical seal and prolong the service life of mechanical seal.
2. Problems easy to occur in the mechanical seal of water pump
In the process of use, the main problems of mechanical seal are excessive leakage and high temperature. Touch the mechanical seal gland by hand. If it cannot stay on it, it indicates that the temperature is too high. The leakage amount on each side shall not exceed 60 drops / min. if it flows in a linear shape, it indicates that the leakage amount is too large. It can be determined whether to observe the operation; If the fuel is injected outward, stop the engine immediately for inspection.
3 control measures taken
3.1 ensure the quality of parts
Before leaving the factory, the mechanical seal must be tested for sealing performance and have a certificate of conformity. After long-term operation of the mechanical seal, the wear of the moving ring and the static ring, the corrosion and wear of the spring and shaft, the wear, aging and deformation of the sealing rubber ring can cause the leakage of the seal, which must be repaired or replaced with new parts. The sealing surfaces of the moving ring and the stationary ring shall be free of cracks, missing corners, scratches, pitting, flash and eccentric wear, and the scratches and pitting shall not penetrate the whole sealing end face. If the repaired dynamic and static ring is used, the sum of the boss heights of the dynamic and static ring shall not be less than 3mm, and the height of a single boss shall not be less than LMM, so as not to affect the heat dissipation. After the installation of the moving ring, it shall be able to move flexibly on the shaft. After pressing the moving ring against the spring, it shall be able to bounce back freely to keep the vertical and parallel of the moving and stationary rings. The specification of the dynamic and static ring sealing rubber ring shall comply with the drawing, and the surface shall be free of damage, uneven thickness and uneven hardness. The sealing rubber ring shall be replaced during overhaul. The outer surface of the spring shall be clean and free of rust. Before use, the length and shape detection and pressure test shall be carried out. The pressure difference of each group of springs in the specified compression length shall meet the requirements, and the pressure error of each group of springs in the specified compression length shall meet the requirements. The allowable deviation of free length shall not exceed 0.5mm, and the compression amount shall not be too large or too small. The required error is ± 2mm. The seal sleeve and the pump shaft cannot be made of the same material, and the parallelism tolerance of the end faces on both sides and the non perpendicularity tolerance with the axis shall not exceed ± 0.20mm.
3.2 ensure sufficient cooling and lubrication
Adjust the opening of the regulating valve of the cooling pipeline to ensure that the cooling pipeline of the mechanical seal is unobstructed. Open the emptying valve when the tank water pump is opened to exhaust the gas in the sealing cavity.
3.3 ensure installation accuracy
When disassembling the mechanical seal of the water pump, the dynamic and static rings shall be cleaned, and a small amount of clean lubricating oil shall be applied on the friction pair surface. The high-pressure end and low-pressure end shall be considered, and collision is strictly prohibited. When installing the static ring gland, the force shall be uniform to prevent pressure deviation. Check with a feeler gauge. The deviation of the upper, lower, left and right positions shall not be greater than 0.05mm; Check the fit clearance between the gland and the outer diameter of the shaft. It shall be uniform around, and the allowable deviation of each point shall not be greater than 0.1ram. The radial runout of the pump shaft where the mechanical seal of the water pump is installed shall not exceed 0.05mm. Before connecting the pump cover and seal end cover, carefully review the installation and positioning dimension of the mechanical seal. If the positioning dimension does not meet the requirements, it can be adjusted with a steel pad between the shaft sleeves, but the precision of the steel pad shall be high, and the thickness difference shall not exceed 0.01mm. Measure the radial runout of the mechanical seal sleeve and the end face runout of the sealing surface to meet the requirements.
For the operating mechanical seal, if the gland is loose and the sealing surface moves, the dynamic and static ring parts must be replaced and shall not be tightened again for further use. Because after such loosening, the original motion track of the friction pair will change, and the sealing performance of the contact surface is easy to be damaged.
4.4 adjust the end face specific pressure
The specific pressure of the end face is an important parameter related to the sealing performance and service life. It is related to the structural type of the seal, the size of the spring and the medium pressure. Excessive specific pressure on the end face will damage the friction pair; If the specific pressure is too small, it is easy to leak. The manufacturer often gives a suitable range, and the specific pressure of the end face is generally 3 ~ 6kg / cm2. Adjusting the specific pressure is to adjust the compression size of the spring. The free length of the spring is represented by a, the load borne by the spring stiffness when generating the unit compression is k, and the specified specific pressure is represented by P. these are the parameters given by the manufacturer. The dimension after compression is represented by B, then p / A-13 = k, and 13 = A-E / K is obtained, which is the dimension after spring installation and compression. If the size of the spring after installation is too large, the thickness of the adjusting pad can be increased between the spring seat and the spring. If the size is too small, the thickness of the adjusting pad can be reduced. The thickness of the adjusting pad shall be measured with a micrometer.
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