| 摘要 |
<p>The valve consists of two rectangular pieces of thermoweldable film (50, 51), one of which has an aperture (52). A filter square (53) is sandwiched between the films and held at its four corners by welds. The valve is then attached to the outside of the sack, opposite an aperture (62), by a ring of weld (61) which completely encloses the filter area. The two pieces of film are then completely welded together (63) except for one end (64) which is left open. When the sac has been filled with granular material it is evacuated via the open end of the valve which is then sealed by weld.</p> |
