Leak-tight seal, establishing

Establishing a leak-tight seal for new brass valves in new steel cylinders... 

Using a predetermined amount of torque to establish a leak-tight seal also has some drawbacks. Variations in coefficients of friction, thread damage, type of sealant used, and other factors can influence the amount of applied torque that is necessary to create a seal. For example, if the first thread on the cylinder valve is severely damaged, much of the torque may be used just to overcome the resistance of the damaged thread. 

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