Looseness of connection of moving parts of a chain drive pumping unit is one of the main factors causing the impact of the unit in reversing.

• 链条等传动件的联结松弛是导致链条抽油机换向冲击的主要原因。冲击造成机件损坏的过程缓慢而渐进，达到一定程度可导致链条断脱、特殊链节失效、链轮轴滚键等事故。