How To Maintain The Mechanical Seal Of Centrifugal Pump (selection Of Mechanical Seal For Centrifugal Pump)
Sep 21, 2024
Maintenance of mechanical seal for centrifugal pump
The mechanical seal of centrifugal pump is a key consumable of centrifugal pump, and its service life will gradually shorten after long-term operation. How to extend the service life of centrifugal pump mechanical seals? We have strong maintenance skills for centrifugal pump mechanical seals to help extend their lifespan.
1. Cleaning and inspection of mechanical seal maintenance
The working principle of mechanical seal maintenance for centrifugal pumps stipulates that there should be no other residue inside the mechanical seal. Before assembling the mechanical seal for maintenance, thoroughly clean the moving ring, stationary ring, shaft sleeve, and other components. Check whether there are scratches, cracks, and other defects on the surface of the dynamic and static rings, which can cause serious leakage of the mechanical seal. If conditions permit, tools can be used to check whether the sealing surface is flat. If the sealing surface is not flat, the working pressure medium will enter the sealing surface of the assembled mechanical seal's dynamic and static rings, separating the dynamic and static rings and causing mechanical seal failure. If necessary, fixtures can also be made for hydrostatic testing before assembly;
2. Technical specification verification for mechanical seal maintenance and assembly
Accurately measure the external dimensions of the sealing surface of the dynamic and static rings. This statistical data is used to verify the radial width of the dynamic and static rings. When using different friction materials, the radial width of the hard material friction surface should be 1-3mm larger than that of the soft material, otherwise it may cause the edges and corners of the hard material end face to be embedded into the soft material end face. Check the gap between the dynamic and static rings and the shaft or shaft sleeve. The inner diameter of the static ring is usually 1-2mm larger than the shaft diameter. For the dynamic ring, in order to maintain suspension, the inner diameter is 0.5-1mm larger than the shaft diameter to compensate for shaft vibration and deflection. However, the gap cannot be too large, otherwise it will cause the sealing ring of the dynamic ring to get stuck and damage the mechanical seal function of the centrifugal pump;
3. Grinding of the end faces of the moving and stationary rings
After the moving ring is removed, it is processed by cutting, and rough grinding is completed first, followed by fine grinding. If conditions permit, polishing can be done well. When rough grinding, use high grain abrasives to first remove production and processing marks. Subsequently, precision grinding is carried out to achieve the design standard for smoothness. Hard alloy or ceramic dynamic rings need to be polished with a polishing machine after precision grinding. The amplitude of the polishing machine can use boron carbide. Polish and polish to achieve a mirror finish. Ceramic rings can be finely ground with agate powder and then polished with chromium oxide. The static ring filled with graphite and polytetrafluoroethylene needs to be finely ground with kerosene, gasoline, or water due to the softness of the raw material, without the need for grinding agents. During the entire running in process, it can also be self-developed, so the smoothness requirement is not too high. The grinding method can be used for those with a grinder, while for those without a grinder, an 8-shaped manual grinding method can be used for flat glass;
4. Shaft sleeve inspection
After disassembling the mechanical seal shaft sleeve for maintenance, check the condition of rust and damage. If the rust or wear is minor, use fine sandpaper to polish it before use. If the rust or wear is severe, use electroplating after production processing or replace the shaft sleeve;
5. Sealing ring
After a period of use, mechanical seals often lose their elasticity or age, and usually need to be replaced with new ones;
6. Spring
If the mechanical seal spring is not severely rusted and can maintain its original elasticity, it does not need to be replaced. If the corrosion is severe or the elasticity is greatly reduced, it is necessary to replace the spring with a new one. For mechanical seals with assembly boxes, the boxes should be cleaned thoroughly and the grooves should be checked for wear or deformation, in order to facilitate calibration and repair, re slotting or replacement. After repairing the mechanical seal components, repeat the assembly process and conduct a working pressure test before putting them back into normal use.
To effectively maintain the mechanical sealing surface of the centrifugal pump without leakage, the dynamic and static surfaces can be compressed on the fitter platform, and water can be poured over for leakage testing. If the static water does not leak, it indicates that the surface roughness, precision, and flatness of the sealing surface meet the requirements. The vertical deviation of the end face during installation shall not exceed 0.015mm.
Selection of mechanical seals for centrifugal pumps
When selecting mechanical seals for centrifugal pumps, sealing pressure is one of the important parameters to consider. The working speed of the seal is an important factor affecting the stability of operation and the wear of the sealing end face. Mechanical seals with general working temperature can be applied. For mechanical seals working at high and low temperatures, in addition to selecting suitable auxiliary systems, it is also necessary to fully consider the sealing materials and structure. Mechanical seal auxiliary systems can also be used to achieve cooling, lubrication, and filtration through different flushing methods, creating a favorable environment for the reliable operation of mechanical seals.
1, Physical and chemical properties of the medium
For media that are not corrosive or have weak corrosiveness, internal mechanical seals can be used. For highly corrosive media, due to the difficulty in selecting springs in elastic components, external mechanical seals can be used when the pressure is low. For media that are prone to crystallization, contain solid particles, and have high viscosity, spring mechanisms should be used. For flammable, explosive, toxic and other media that are prohibited from leaking, dual mechanical seals must be considered to ensure safety.
2, Sealing pressure
Sealing pressure is one of the important parameters to consider when selecting mechanical seals. In general, when the sealing pressure is less than 0.7Mpa, both balanced and unbalanced mechanical seals can meet the requirements for use. When the sealing pressure is between 0.7~12Mpa, consider using a balanced mechanical seal. When the sealing pressure is greater than 12Mpa, consider using a series sealing form (non pressure dual mechanical seal) to achieve step-by-step pressure reduction.
3, Sealing working speed
The sealing working speed refers to the linear velocity of the sealing working surface, which is an important factor affecting the stability of operation and the wear of the sealing end face. When the linear velocity is greater than 30m/s, it is usually referred to as a high-speed seal, and a static mechanical seal should be selected. The end face materials of the dynamic and static rings should also be specially treated to meet the wear requirements.
4, Working temperature
The working temperature usually refers to the temperature of the medium inside the sealed chamber. When the working temperature is below 80 ℃, general mechanical seals can be used. For easily vaporized media, the working temperature should be considered simultaneously with the pressure to be 13.9 ℃ lower than the boiling point, otherwise it is difficult to ensure a stable liquid film between the sealed friction pairs. Mechanical seals with medium temperatures between 80-150C are considered ordinary seals, while mechanical seals with temperatures above 150C are considered high-temperature seals. For high-temperature sealing, an auxiliary system with a heat exchanger is usually used according to specific operating conditions to control the temperature of the medium inside the sealing chamber within a reasonable range, ensuring that the temperature of the sealing ring and friction pair does not exceed the usage limit specified in the specific sealing technology conditions. Mechanical seals used below 20 ℃ are low-temperature seals. For mechanical seals working in low-temperature environments, in order to avoid the freezing of moisture in the external air of the friction pair, an auxiliary system is usually required to use nitrogen blowing to remove steam. For mechanical seals working at high and low temperatures, in addition to selecting suitable auxiliary systems, it is also necessary to fully consider the sealing materials and structure.
5, Mechanical seal auxiliary system
A good liquid film exists between the end faces of the mechanical seal to ensure that there is no dry friction on the sealing end face, and that the corresponding auxiliary components do not fail due to dissolution, denaturation, and aging under working conditions, which is a necessary condition for the reliable operation of the mechanical seal. However, under various harsh working conditions such as high temperature, low temperature, high pressure, and poor lubrication of the medium, relying solely on the form and materials of the mechanical seal itself is difficult to meet the requirements for use. Usually, mechanical seal auxiliary systems are used to achieve cooling, lubrication, and filtration through different flushing methods, creating a favorable environment for the reliable operation of mechanical seals.
We develops and produces all kinds of pumps, roots blowers and related complete sets of equipment. It is a key backbone of general machinery and a national high-tech enterprise. It can provide scientific research and development, design consultation, production, sales and other services. The company is located in Boshan District of Zibo City, which is known as the "famous pump city of China", with convenient transportation conditions.
Professional team
Our factory has the advanced B-grade testing station of computer-controlled submersible motor pump, national 2-grade physical-chemical measurement and inspection center, own the only province-grade investigate institution in Shandong and own the advanced machining centre, computer center and product inspection center. Our factory covers an area of 150000 square meters, with 649 employees and more than 240 technicians above college level, accounting for more than 35% of the total number of employees.
7x24 hours delivery
Located in 27 cities around the world,with 50 delivery centers,providing 200+ languages,7x24 hours delivery capacity,is the best partner for enterprise globalization
134M
Total Freelancer
632M
Positive Review
380M
Order recieved
936M
Projects Completed