1. Initial Symmetrical Pre-Tightening

Begin by hand-tightening all flange bolts to ensure each makes full contact with the flange surface and the gasket between the valve and pipe flanges. Follow a symmetrical pattern during hand-tightening—after turning one bolt a small amount, move to the bolt directly opposite it before proceeding to the next.

This even distribution of initial pressure prevents uneven compression of the gasket or warping of the flange, both of which can lead to leakage once the valve is in use. Ensure every bolt is hand-tightened to a consistent degree, with no bolt left noticeably looser than others.

2. Gradual Torque Increase

Use a torque wrench to apply force in incremental stages, rather than tightening any single bolt to its full recommended torque immediately. Start with a lower torque value that is a portion of the final required torque, maintaining the same symmetrical sequence as the hand-tightening step.

Increase the torque in small, consistent increments with each subsequent pass. This gradual approach allows the gasket to compress slowly and settle into the flange joint, avoiding damage to the gasket or distortion of the flange that can occur from sudden, excessive force.

3. Cyclic Retightening

After reaching the initial target torque for all bolts, perform multiple rounds of retightening using the same symmetrical order. Bolts tightened earlier may loosen slightly as the gasket continues to compress and adjust to the flange pressure.

Each cyclic pass helps balance the torque across all bolts, ensuring uniform pressure on the gasket. Repeat this process until no further adjustments are needed—this sign indicates that the gasket has fully seated and all bolts are evenly tensioned, creating a stable seal.

4. Final Inspection and Verification

Conduct a final check of each bolt’s torque with a calibrated torque wrench to confirm all meet the manufacturer’s specified values. Visually inspect the flange joint for any gaps between the flange surfaces or signs of gasket extrusion, which would suggest uneven tightening.

• If required by the application, perform a pressure test on the assembled valve and pipe system to verify the seal—absence of leakage confirms the tightening sequence was executed correctly.
• Record the final torque values and inspection results for future maintenance and reference purposes.