Dr. Duane Priddy, Plastic Failure Labs
A toilet ballcock valve assembly was sold preinstalled in a toilet tank. The retaining nut is factory installed at the factory using at a prescribed torque and the installation does not leave any tool marks on the retaining nut. Our experts determined that the failure of the ballcock material in the threaded shank was due to tensile overload on the material resulting from over-tightening of the retaining nut. Tool marks were found on the retaining nut left by someone who felt the need to give the nut an extra turn resulting in a stress overload on the material.