main jack meaning in Chinese

电源插座
主起落架动作筒
主千斤顶

When the main jacks of the front supports are released , the structure rests hung to these beams
当前支撑的主千斤顶松开时，结构就吊在这些梁上。
The whole system is supported by the main jack arrangement when concreting , placed at the front supporting bracket and the ( rear ) suspension gallows ? or on supporting brackets only at the start and expansion joint spans
整个系统在混凝土浇注过程中由前牛腿及（后）吊架上主千斤顶系统支撑，在起始段和伸缩缝处则在前后牛腿处支撑。