我处1988年购进一台日立公司牛产的UH181型反铲挖掘机，运转到9450h突然发生下列故障：左侧履带停驶，大臂起升速度变慢，铲斗挖掘无力，但其它动作正常。在此之前，该机未发现液压或机械故障前兆。1故障分析根据行走液压系统原理图分析，发生上述故障的可能原因有：门）左行走 In 1988, we purchased a UH181 backhoe excavator from a Hitachi cow. During the operation to 9450h, the following faults suddenly occurred: the left crawler was stopped, the boom lifting speed was slow, and the bucket was digging, but other actions normal. Prior to this machine did not find hydraulic or mechanical failure precursors. 1 Failure Analysis According to the hydraulic system schematic diagram of walking, the possible causes of the above failures are: door) left walk