放松制动器，重物即可自行快速下降，缩短返程时间，但这种千斤顶构造较复杂。
Relaxes the brake, the heavy item then voluntarily fast drops, reduces the return trip time, but this kind of hoisting jack structure is complex.
自降螺旋千斤顶的螺纹无自锁作用，装有制动器。
From falls screw jack's thread non-self-locking action, is loaded with the brake.
自降螺旋千斤顶的螺纹无自锁作用，装有制动器。
From falls screw jack's thread non-self-locking action, is loaded with the brake.
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