If proper bolt tightening sequences are not followed or if improper torque is applied to the bolts, sealing problems will result (see Picture 1). A slight bow in the flange or lid top (exaggerated for illustration) occurs, which applies uneven pressure to the gasket. This bow compromises the seal, and the gasket will eventually leak. Picture 2 illustrates proper bolting sequences for various type flanges/covers. Bolt numbers show the correct tightening sequences. The numbers do not have to be followed exactly; however, the diagonal tightening patterns should be followed. By using proper torque and the illustrated sequence patterns, sealing problems from improper tightening and uneven pressure on the gasket can be avoided. Use a torque wrench and torque bolts according to the head stamp on the bolt. Check the manufacturer’s instruction book for pancake gasket torque values.
Picture 1: Bowing at Flanges
Picture 2: Bolt Tightening Sequences
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