1、固定式升降货梯液压泵输油量不足，包括固定式升降货梯液压泵泵油量不够，吸油阻力过大，吸油管道漏气，油液黏度过大或油温太低，油箱中油面高度过低以及油箱通气孔堵塞。
Stationary hydraulic cargo lifter insufficient amount of oil, including fixed cargo lifter hydraulic pump enough oil, oil resistance is too large, oil pipeline leaks, oil viscosity is too large or too low oil temperature, oil tank surface height is too low and a fuel tank vent clogged.

2、固定式升降货梯液压泵内泄漏严重，如零件磨损过大、密封问隙变大、泵体因铸造缺陷等，使压油腔和吸油腔连通。
Fixed cargo lifter pump leak serious, such as too much wear and tear parts, seals ask gap becomes larger, the body due to casting defects, so that the pressure oil chamber and the suction chamber in communication.
  
3、固定式升降货梯压力油路的管接头及各种阀的泄漏，如固定式升降货梯液压缸、液压马达的密封装置损坏，引起内泄漏严重。
Fixed cargo lifter pressure oil leakage of various valves and fittings, such as fixed cargo lifter hydraulic cylinder, hydraulic motor seal damage, causing severe internal leakage.