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The Structure and Development of Sleeve Compensators
Release time:
Aug 19,2021
The sleeve compensator is an age-old type of pipeline expansion joint. Due to its large compensation capacity, low resistance, low cost, and long service life of the sleeve body, it was widely used until the 1970s. However, it suffered from frequent leaks at the sealing points, necessitating regular maintenance. After the 1980s, when bellows expansion joints began to be applied in pipeline systems, they gradually captured a larger market share. Yet, during their use, problems such as short-term failure due to factors including material quality, water conditions, and installation practices emerged. Coupled with their high cost, attention once again turned toward the use of sleeve compensators. Meanwhile, in the early 1990s, to overcome the sealing defects and eliminate the axial forces generated by medium pressure, elastic sleeve compensators were successively developed.
The sleeve compensator is an age-old type of pipeline expansion joint that has been widely used since before the 1970s due to its large compensation capacity, low resistance, low cost, and long service life of the sleeve body. However, it suffers from frequent leaks at the sealing points, necessitating regular maintenance. After the 1980s, when bellows expansion joints began to be applied in pipeline systems, they gradually captured a larger market share. Yet, during their use, problems such as short-term failure due to factors including material quality, water conditions, and installation practices emerged. Coupled with their relatively high cost, attention once again turned to the use of sleeve compensators. Meanwhile, in the early 1990s, to overcome the sealing defects and eliminate the axial forces generated by medium pressure, elastic sleeve compensators and thrust-free sleeve compensators, along with new sealing structures and materials—including oil-sealed designs—were successively developed. These innovations not only boosted the adoption of sleeve compensators but also spurred the further development of bellows expansion joints, thanks to the structural advancements introduced by thrust-free compensators. Patent searches reveal that China has taken a leading position in the field of sleeve compensators.
There are many enterprises producing sleeve compensators. To standardize the development and application of sleeve compensators and improve product quality, China’s Ministry of Construction issued an industry standard for welded sleeve compensators used in urban heating systems in 1994.
The sealing structure of the sleeve compensator employs both packing seals and mechanical seals. The packing seal is a contact-type seal in which an elastic sealing material is packed between the outer sleeve and the core tube. After the packing is compressed by an axial force, it tightly adheres to the surface of the core tube. The elastic deformation of the sealing material compensates for wear on the sealing surfaces, thereby preventing leakage of the medium. Since the packing exhibits both elasticity and plasticity, the radial forces generated by the axial force along the depth of the packing are uneven, resulting in a pressure coefficient.
Due to this characteristic, packing materials have evolved from single-material configurations to combined-use designs—for example, hard packing placed in the deeper sections, soft packing near the gland, or a sealing oil layer inserted between the hard and soft packings. In the event of leakage, auxiliary oil injection can be used to stop the leak, or alternatively, a fully oil-sealed packing structure can be employed.
In the past, mechanical seals were primarily used as dynamic seals for rotating shafts. They consist of at least one pair of end faces perpendicular to the axis of rotation, which, under the action of fluid pressure and the elastic force of a compensation mechanism, remain in close contact with and slide relative to another end face, thereby preventing fluid leakage. For this reason, they are also referred to as face seals. Currently, these seals have reached the following performance levels: maximum rotational speed of 50,000 rpm, maximum linear velocity of 150 m/s, operating pressures up to 35 MPa, service temperatures as high as 1,000°C, shaft diameters up to 1,000 mm, allowable leakage rates ranging from 3 to 0.1 mL/h, and service lives spanning from 1 to 15 years. Therefore, using this sealing technology to address the sealing requirements of sleeve compensators is entirely feasible. However, it also entails significantly higher geometric tolerance and fit precision requirements, leading to a substantial increase in costs.
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