1. Preparation before installation
Inspection of valves and tools
Check the specifications and models of the valves, confirm that there is no damage to the appearance, and that the valve stem, butterfly plate and other parts are moving normally;
Prepare tools: bolt and nut set (adapted to the flange aperture), gasket (rubber or metal spiral wound gasket), torque wrench, and cleaning agent (such as alcohol).
Pipe and flange treatment
Clean the connection surface of the pipeline flange, remove oil, rust and welding residues, and ensure that the sealing surface is flat and scratch-free;
Check whether the pipeline flange holes are aligned, and the center distance of the bolt holes must be consistent with the valve body flange.
2. Core installation steps
Pre-joint flange and valve
Place the butterfly valve between the two pipeline flanges, manually adjust the flange to align the bolt holes, and insert a small number of bolts (such as two at the top) to temporarily fix it to calibrate the concentricity;
Note: The butterfly plate needs to be kept slightly open (about 5%-10% opening) to avoid deformation of the sealing ring due to high welding temperature.
Flange welding fixation
Use spot welding to initially fix the pipeline flange on the pipeline, then remove the valve and complete the full-circle welding of the flange and the pipeline (avoid the welding heat being directly transferred to the valve body);
After welding, it needs to be cooled to room temperature to prevent thermal expansion from causing flange deformation.
Gasket installation and valve connection
Place gaskets evenly on the flange sealing surface (one side or two sides according to the working conditions), and ensure that the gaskets are centered without offset;
Reinstall the butterfly valve, insert all bolts and pre-tighten them by hand, and tighten them in diagonal order in batches (such as 50% torque for the first time, 80% for the second time, and 100% for the third time).
3. Commissioning and acceptance
Functional test
Manually rotate the handwheel or operate the actuator to confirm that the butterfly plate can be fully opened and closed without obstruction, and the valve stem can rotate flexibly;
Open the valve to the maximum opening and check whether the edge of the butterfly plate interferes with the inner wall of the pipeline.
Sealing Verification
Perform a pressure test (1.5 times the working pressure), maintain the pressure for 5 minutes, and observe whether there is leakage at the flange connection and the valve stem seal;
If it is a pneumatic/electric valve, it is necessary to simultaneously verify the consistency of the actuator stroke and the valve opening.
4. Precautions
Bolt tightening specifications: Avoid excessive pressure on one side to cause flange warping. It is recommended to use a torque wrench and operate according to the manufacturer's recommended value;
Welding protection measures: Wrap the valve body with fireproof cloth during welding to prevent splashes from damaging the sealing surface or the inner coating of the valve body;
Regular maintenance: Retighten the bolts after 1 month of operation, and check the wear of the seals and the flange connection status every six months thereafter.
