The Difference Between Metal Bellows Mechanical Seal and Ordinary Mechanical Seal

The welded metal bellows mechanical seal has good floating and random compensation, which can compensate the leakage of the sealing ring due to wear, axial movement and vibration. The welded metal bellows itself serves as both an elastic element and a seal, so there is no need to design the dynamic auxiliary sealing ring of the general push-ring type spring-type mechanical seal, thereby avoiding the fine particle blockage caused by the dynamic auxiliary sealing ring. The seal is not resistant to high temperature and has the problem of reducing the seal compensation ability due to the axial friction resistance generated.

1. Advantages of metal bellows mechanical seal compared with ordinary mechanical seal

There is no auxiliary sealing ring in the middle of the metal bellow mechanical seal, which reduces a leakage point; at the same time, it reduces the frictional resistance of the compensation mechanism and improves the followability; in the petrochemical industry, the service temperature of the welded bellows seal is not limited by the auxiliary sealing ring; For PTFE bellows seals can be used in corrosive media.

The welded metal bellows is tightly welded by the inner and outer diameters of each wave plate, so no matter whether it is used as a static or rotating type, it is not necessary to consider the problem of rotation. Welded metal bellows can be made of precipitation-hardening stainless steel, high-temperature nickel-based materials and chromium-nickel corrosion-resistant materials, so welded metal bellows can be applied to a wider temperature range and various acid, alkali and salt media. Choose different wave plate thicknesses and layers to withstand pressures up to 7MPa in special pumps. The welded metal bellows mechanical seal is generally designed as a balanced type, so its bearing pressure has little effect on the specific pressure of the end face. The welded metal bellows mechanical seal is not only suitable for non-hydrocarbon media, but also suitable for flash hydrocarbon media. Compared with ordinary mechanical seals, its service life has also been greatly improved, so it has a higher performance-price ratio.

2. Features of metal bellows mechanical seal

(1) Good floatability. One of the most notable features of the metal bellows mechanical seals is its good floatability. It is therefore insensitive to shaft vibrations, yaws and deflections of the rotating shaft to the housing bore. For example, the mechanical seal for the kettle with large deflection, the seal with severe vibration and the deflection caused by improper installation, the bellows mechanical seal has a good adaptability and obtains a satisfactory sealing effect.

(2) The secondary dynamic sealing ring is canceled. Therefore, the high temperature resistance, corrosion resistance, gas escape and loss of elasticity of the rubber are excluded, and the tendency of relaxation caused by the use of PTFE wedge rings and U-shaped sealing rings, and the fact that it is difficult to maintain its original shape under load, The disadvantage of sealing materials losing their sealing effect due to creep and hardening at high or low temperatures.

(3) The shaft or sleeve is not subject to wear. Since the auxiliary sealing ring of the metal bellows mechanical seal can be designed as a relatively static seal, there is no axial displacement between the shaft or the sleeve, thereby avoiding the wear of the shaft or the sleeve.

(4) The metal bellows mechanical seal is designed as a static type, which has good anti-evacuation and anti-unbalance performance, so it is very suitable for pumps that often have evacuation due to process reasons.

(5) It is more suitable to use metal bellows for high temperature and flammable media. Because high-temperature pyrolyzate deposits can block the spring. On the other hand, under high temperature conditions, the dynamic sealing ring is also the weakest link.

(6) Metal bellows mechanical seal, because the inside or outside of the bellows is filled with sealed liquid to maintain pressure balance, it can obtain a smaller end face specific pressure and prolong its life.

(7) Simple structure and easy installation. The bellows is not only used as a transmission element to drive the seal ring to rotate, but also can be used as a compensator to generate spring specific pressure and reduce the dynamic seal ring, so it is simpler than conventional mechanical seals and easy to install.

(8) Wide application range. The bellows mechanical seal parts choose different materials and structures according to different conditions of use, and it is particularly effective in solving corrosive media, high temperature, low temperature, high pressure and high speed sealing. For example, double-layer welded metal bellows solves high-pressure sealing, and metal bellows solves high-temperature and low-temperature media.

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