During the installation of a BSP thread with captive seal, preventing excessive compression and deformation of the sealing ring is crucial to ensuring sealing performance and service life. BSP thread with captive seals are divided into parallel thread (BSPP) and tapered thread (BSPT). BSPP relies on the sealing ring for sealing, and the installation quality of the sealing ring directly affects the reliability of the system. The following details specific measures to prevent excessive compression and deformation of the sealing ring from seven aspects: installation preparation, tool selection, operating procedures, material matching, pressure control, environmental adaptation, and maintenance inspection.
Preparation before installation is fundamental to preventing sealing ring deformation. Before installation, the threaded interface and sealing ring must be thoroughly cleaned to avoid impurities scratching the sealing ring surface or affecting the sealing effect. Simultaneously, check whether the sealing ring specifications match the dimensions of the BSP thread with captive seal, ensuring that the inner diameter, outer diameter, and cross-sectional diameter of the sealing ring meet the design requirements. If the sealing ring is too small, it is easily overstretched during installation; if it is too large, insufficient compression may lead to leakage. In addition, it is necessary to confirm that the material of the sealing ring is suitable for the working environment. For example, fluororubber (VITON) is suitable for high-temperature and chemically corrosive environments, while nitrile rubber (NBR) is more suitable for petroleum-based media.
Using specialized tools can effectively prevent damage to the sealing ring during installation. When installing manually, avoid using sharp tools to directly push the sealing ring to prevent scratching or shearing the sealing surface. It is recommended to use plungers or push rods made of soft resin with a smooth, rounded top design to evenly distribute pressure and reduce the risk of localized deformation. For combined sealing rings (such as Step seals or Glyd rings), the O-ring and slip ring should be combined first before installation as a whole to prevent uneven stress on the sealing ring due to misalignment during individual component installation. Furthermore, when passing through threaded, keyway, or sharp-edged areas, a special guide sleeve can be used to protect the sealing ring lip from scratches.
Following operating procedures is crucial to preventing sealing ring deformation. During installation, the sealing ring should be manually pre-installed to the starting position of the threaded interface, and then slowly pressed in using a specialized tool, avoiding forceful impact or rapid insertion. For lip seals, ensure the lip direction aligns with the medium pressure direction to prevent reverse installation that could cause the lip to roll over or tear. When tightening a BSP thread with a captive seal, control the tightening torque to avoid over-tightening and squeezing the seal out of the groove gap. For example, in low-pressure scenarios, BSPP threads typically rely on the elastic deformation of the seal to achieve a seal; excessive tightening torque may lead to permanent deformation or breakage of the seal.
The appropriateness of material matching directly affects the seal's compression resistance. Seals made of different materials have different compression deformation characteristics, requiring the selection of suitable materials based on the working environment. For example, silicone rubber (SIL) has excellent high and low temperature resistance but low tensile strength, making it unsuitable for high-pressure scenarios; polyurethane rubber (PU) has excellent wear resistance and high-pressure resistance, but is prone to hydrolysis at high temperatures and should be avoided in high-temperature media. Furthermore, the seal's hardness is also a critical parameter; excessive hardness may reduce sealing performance, while insufficient hardness makes it susceptible to deformation under pressure. Typically, the recommended compression for dynamic seals is 20% of their diameter, and for static seals, 30%, to ensure a good seal while preventing excessive deformation.
Precise pressure control is crucial to preventing seal deformation. In high-pressure scenarios, seals must withstand higher radial pressure. This requires optimizing the groove design or adding a retainer ring to distribute the pressure. For example, when the working pressure exceeds a certain value, a retainer ring can be added to one side of the seal root to prevent it from being squeezed out of the groove. The retainer ring should be installed in the opposite direction to the medium pressure to effectively prevent axial movement of the seal. Furthermore, composite lip rings or metal-rubber seals are recommended for high-pressure scenarios. These seals have higher compressive strength and wear resistance, and are better suited to high-pressure environments.
Environmental adaptability considerations can extend the service life of seals. In high-temperature environments, seals are prone to hardening or cracking due to thermal aging. High-temperature resistant materials (such as fluororubber) must be selected, and the operating temperature must be controlled within the material's allowable range. In low-temperature environments, seals may lose elasticity due to shrinkage. Low-temperature resistant materials (such as silicone rubber) must be selected, and rapid temperature changes should be avoided. Furthermore, in chemically corrosive environments, corrosion-resistant materials (such as fluorosilicone rubber) must be selected, and the surface of the sealing rings should be regularly inspected for signs of aging such as swelling and cracks.
Regular maintenance and inspection are essential to ensure the long-term effective operation of the sealing rings. During equipment operation, the sealing rings should be regularly inspected for leaks, deformation, or signs of aging. If any problems are found, they should be replaced promptly. When replacing the sealing rings, the threaded interface and grooves must be thoroughly cleaned to remove contaminants, and the bottom surface of the grooves should be polished to ensure a tight fit of the new sealing ring. At the same time, avoid using old sealing rings or sealing rings of different specifications to prevent seal failure due to size mismatch.
