Universal flange adapters are core components for pipeline connections in heating, ventilation, and air conditioning systems, undertaking the sealing and pressure-bearing functions for the transportation of hot and cold media. Their installation quality directly affects the operational efficiency, sealing performance, and service life of the system. In view of the characteristics of HVAC systems, such as large and medium temperature fluctuations, high vibration frequency, and strict sealing requirements, standardised installation procedures must be followed and key technical points controlled.
I. Pre-installation Preparation Work
1. Inspection of Materials and Accessories
Verification of Flange Adapter Selection: Confirm that the pressure rating and nominal diameter of the universal flange adapter are fully matched with the pipeline specifications. The material shall be suitable for the system medium. For air conditioning water systems, carbon steel galvanized flanges or 304 stainless steel flanges are preferred to avoid rust and pipeline blockage. For corrosive media, 316 stainless steel flanges shall be adopted.
Selection of Sealing Gaskets: Select gaskets according to system working conditions. For ordinary air conditioning water systems, rubber asbestos gaskets or EPDM rubber gaskets can be used. For high-temperature hot water systems, flexible graphite gaskets are required. Damaged, aged, or uneven-thickness gaskets are strictly prohibited. The inner diameter of the gasket should be slightly larger than the pipeline inner diameter, and the outer diameter should be smaller than the outer diameter of the flange sealing surface.
Inspection of Fasteners: Bolts and nuts must be matched with flanges, and their material strength grade should not be lower than Grade 8.8. The threads shall be free from slipping and rusting, with complete matching flat washers and spring washers to ensure uniform force during the fastening process.
2. Pre-treatment of Pipelines and Flanges
Processing of Pipeline Ends: The pipeline connection ends shall be cut flat, with the perpendicularity deviation ≤ 0.5mm/m, free from burrs, grooves, or deformation. Use a grinder to polish the outer wall of the pipeline and the flange sealing surface, remove impurities such as oil stains, rust, and oxide scale to expose the metallic luster, and avoid impurities affecting the sealing effect.
Pre-assembly of Flange Groups: Slide the flange over the pipeline and fix it by welding or threaded connection. Ensure that the flange sealing surface is perpendicular to the pipeline axis, with the coaxiality deviation ≤ 1mm. During welding, protective measures shall be taken for the sealing surface to prevent welding slag splashing and damaging the sealing surface.
3. Preparation of Construction Tools and Environment
Equipped with special tools such as a torque wrench, level ruler, feeler gauge, and flange spreader. The torque wrench shall be calibrated in advance to ensure accurate fastening torque.
The installation area shall be clean and dry, and construction in humid or dusty environments should be avoided. For high-altitude operations, stable scaffolding shall be erected, and safety protection measures shall be taken.
II. Key On-Site Installation Procedures
1. Flange Butt Alignment and Positioning
Adjust the flange sealing surfaces of the two pipeline sections to make them parallel and aligned with uniform gaps. It is strictly prohibited to correct flange deflection by forcibly tightening bolts to prevent flange deformation or excessive stress on bolts.
Use a level ruler and feeler gauge to detect the coaxiality and parallelism of flanges, ensuring that the deviation meets specifications. For large-diameter pipelines, lifting equipment shall be used for auxiliary positioning to avoid flange misalignment caused by the self-weight of pipelines.
2. Installation of Sealing Gaskets
Ensure that the flange sealing surface is clean and dry. Place the gasket flat in the center of the sealing surface. Partial installation, overlapping installation, or multi-layer gaskets are strictly prohibited. For high-temperature and high-pressure working conditions, a thin layer of graphite powder can be evenly applied on both sides of the gasket to enhance sealing performance.
Do not move the gasket at will after installation to prevent gasket displacement and sealing failure.
3. Bolt Fastening Process
Fastening Sequence: Strictly follow the principle of diagonal crossing and step-by-step fastening. Tighten bolts in a "cross-symmetric" or "star-symmetric" sequence to avoid uneven stress on the flange sealing surface caused by unilateral stress.
Fastening Steps: Complete the fastening in 3 steps. First, preliminary tightening to make the gasket evenly fit the sealing surface. Second, intermediate tightening, and use a feeler gauge to check the uniformity of the flange gap. Third, final tightening to ensure uniform force on all bolts.
Torque Control: Determine the fastening torque according to the flange specifications and bolt diameter. Specific values refer to the product technical manual. Over-torque fastening is strictly prohibited to prevent bolt breakage or flange deformation.
III. Installation Quality Acceptance Standards
Visual Inspection: The flange sealing surface shall be free from damage, the length of bolts exposed beyond nuts shall be consistent, and there shall be no gasket extrusion or displacement.
Sealing Performance Test: Conduct a hydrostatic test on the system after installation, with the test pressure being 1.5 times the working pressure. Keep the pressure stable for 30 minutes. Qualified standards require no leakage or pressure drop at flange adapters. For gas medium pipelines, an air-tightness test shall be conducted. Apply soapy water to the flange connections, with no bubbles generated, as per the qualified standard.
