Aluminium is used for the bottom cap for increased durability, lower maintenance and ease of rebuilding.

铝是用于底部的上限，增加耐用性，降低维护和易用性的重建。

Tube cap in the situation of low pressure, remove maintenance, high pressure situation general don't tube cap.

用管帽一般在压力较低的情况下，便于拆卸检修，高中压情况下一般不用管帽。