求翻译：当柱塞位于最上面的位置时，燃油从环形油腔通过柱塞套的上由孔，环形切槽与柱塞的中心孔流入并充满柱塞套内的下部油室，同时也直接从下油孔充满油室。当柱塞向下运动时，柱塞套下油孔先被柱塞的端面遮住，一部分燃油从上油孔压回环形油腔。是什么意思？

When the plunger is located in the top position, fuel from the annular oil chamber through the plunger sleeve, plunger center hole into the hole, annular grooving and filled with the lower oil chamber of the piston kit, and also directly from The hole filled with oil chamber. When the plunger downwa