... Clamp-ring type is our patent product. The quick-opening closure consists of cover, base, start system, seal ring, swiveling jib ... , and it doesnt rotate relatively to the cover when the closure is locked. The trivalvular clamp-ring achieves even stress which ... ), which is designed and manufactured according to SY/TO556-1999 PRC Line Standard for Petroleum and Gas Quick Opening Closure and referring ...