Why should packings not be over-tightened in a centrifugal pump?

In a centrifugal pump, packings are designed to prevent leakage of fluid along the shaft while allowing for some minimal leakage to ensure proper functioning. A slight leakage is beneficial because it helps to cool and lubricate the packing material and the shaft, which can prevent overheating and wear. If packings are over-tightened, it can create excessive friction, leading to increased wear and heat generation. Furthermore, an overly tight packing can lead to complete obstruction of flow, disrupting the necessary lubrication that keeps the pump operating effectively. Therefore, allowing for slight leakage by not over-tightening the packings is crucial for the longevity and efficiency of the pump system.