double casing meaning in English

双层罩
双属外壳

Double case construction fuel tank
双层包箱
This device has many advantage character with lower flow , higher delivery lift , small area for occupying and also has double cases structure , in which internal case is vertical and sectional type and external is simple sack type in order to guarantee safety arriving without any leaking absolutely
该型泵具有流量小、扬程高，占地面积小的优点，该泵为双层壳体结构，内壳为立式节段式，外壳为筒袋式，确保运行安全，达到绝对无泄漏。