Advantages And Disadvantages of Mechanical Seals

Advantages and Disadvantages of Mechanical Seals

1. Advantages

(1) The structure is reliable and the leakage can be limited to very little. As long as the surface roughness and flatness of the main sealing surface can meet the requirements, and as long as the material has good wear resistance, the mechanical seal can achieve very little leakage, even invisible to the naked eye. leakage.

(2) Long life. In mechanical seals, the main wear part is the end face of the seal friction pair. Because the wear amount ofthe seal end face is not large under normal working conditions, it can generally be used continuously for 1 to 2 years. It can also be used for 5 to 10 years in special occasions.

(3) No adjustment is required during operation. Since the mechanical seal relies on spring force and fluid pressure to make the friction pair fit and automatically maintain contact during operation, there is no need to adjust and tighten like ordinary soft packing after assembly.

(4) It has vibration resistance. At a speed of 3000r/min, the maximum amplitude does not exceed 0.05mm and the PV value continues to increase.

(5) Small power loss. The packing seal works on the shaft or sleeve by the compression of the packing. The packing seal is in direct friction with the shaft. The tighter the packing is pressed, the greater the friction and the greater the powerconsumption. The friction of the mechanical seal is in a semi-liquid friction state, and the friction coefficient is very small. The power loss of the mechanical seal is 10 to 50% of that of the packing seal.

(6) The bellows seal shaft or sleeve is not subject to wear and is not sensitive to the vibration of the rotating shaft and the deflection of the shaft to the housing.

(7) Wide scope of application. When the medium is flammable, explosive, toxic and harmful, mechanical seals can be used to ensure sealing. It is also suitable for sealing equipment with high temperature, low temperature, high pressure, vacuum, various speeds and corrosive media.

2. Disadvantages

(1) If the structure is more complex than a packing seal, the processing accuracy is high, and certain installation techniques are required. In particular, the installation requirements of dry gas seals are higher. Moreover, sealing technology is developing rapidly, and the continuous emergence of new technologies has brought new issues to our maintenance.

(2) The structure is complex and it is inconvenient to disassemble and assemble. Compared with other seals, mechanical end face seals have a large number of parts, require precision, and have a complex structure. It is especially difficult to assemble. During disassembly and assembly, the sealing ring must be pulled out from the shaft end, and part of the machine (coupling) or all must be disassembled. Some improvements have been made to this problem, such as the use of split and cartridge mechanical seals that are easy to disassemble and assemble and can ensure assembly quality.

3. Working principle of mechanical seal

Mechanical seals, also known as end face seals, rely on one or several pairs of end faces that slide relative to each other perpendicular to the shaft. Under the action of fluid pressure and the elastic force (or magnetic force) of the compensation mechanism, the mechanical seal relies on the cooperation of the auxiliary seal to maintain fit with the other end, and slide relative to each other to prevent fluid leakage.

4. Selection of commonly used materials for mechanical seals

Clean water, normal temperature: (dynamic) 9Cr18, 1Cr13 surfacing cobalt chromium tungsten, cast iron; (static) impregnated resin graphite, bronze, phenolic plastic.

River water (containing sediment), normal temperature: (dynamic) tungsten carbide, (static) tungsten carbide.

Sea water, normal temperature: (dynamic) tungsten carbide, 1Cr13 surfacing cobalt chromium tungsten, cast iron; (static) impregnated resin graphite, tungsten carbide, cermet.

Superheated water 100 degrees: (dynamic) tungsten carbide, 1Cr13 surfacing cobalt chromium tungsten, cast iron; (static) impregnated resin graphite, tungsten carbide, cermet.

Gasoline, lubricating oil, liquid hydrocarbon, normal temperature: (dynamic) tungsten carbide, 1Cr13 surfacing cobalt chromium tungsten, cast iron; (static) impregnated resin or tin-antimony alloy graphite, phenolic plastic.

Gasoline, lubricating oil, liquid hydrocarbon, 100 degrees: (dynamic) tungsten carbide, 1Cr13 surfacing cobalt chromium tungsten; (static) impregnated bronze or resin graphite.

Gasoline, lubricating oil, liquid hydrocarbons, containing particles: (dynamic) tungsten carbide; (static) tungsten carbide.