The author introduced the construction character and hermetical principle and application in practice of multiple arrangement metal and hard hermetical gas butterfly value.
Conservation: hermetical product can be saved for a yeay in the shade and in the dry place.
The novel and hermetical structure is suitable for operation under the states of both positive and negative pressure.
By 2005, all the gas stations, main oil storage tanks and the oil refinery enterprises in the city should have installed hermetical oil gas recovery facilities.
