upper plunger

例句：

1. 1.The upper plunger was used to lift the heavy object.
   上压柱被用来举起重物。
2. 2. The upper plunger is responsible for maintaining the proper pressure in the system.
   上压柱负责保持系统中适当的压力。
3. 3. The upper plunger was damaged during the installation process.
   在安装过程中，上压柱受损了。