This type of seal utilizes a band of compression plates pushing against the tank wall. Behind of each compression plate one or more leaf spring is used to spring back the compression plates. The plates may be mounted on horizontal or vertical roof rims and made to accept specific bolt pitching. Adjacent compression plates are overlapped and the installation of a flexible vapor barrier which is fitted in between leaf springs and compression plates ensures the vapor tightness of the seal.
Generally speaking, each and every tank has its own particular and unique dimensional and operational parameters; thus, VISTA’s solution covers many different designing aspects considering the Rim Gap space, the particulars of the fluid to be stored, the material of the tank, various geometrical dimensions of the tank, and etc. leading to the construction of a seal according to the needs of customers. In VST – 15 design the following points are of paramount importance: - The vapor Barrier extends downward, into the stored liquid, withholding the vapors and fumes in the tank to the maximum extend. - VST – 15 seals are suitable for tanks with Rim Gap measuring 100 mm – 450 mm with the life expectancy of 10 – 20 years.
The materials selection is carried out in view of the tank’s operational condition taking into account the product stored, ozone factor, UV radiation, rainwater downfall and etc. to reach the best solution and life expectancy for a long and trouble free service at the lowest cost. The material used in VST – 15 is as below: Compression Plates: galvanized mild steel or stainless steel alloys. Channels: galvanized mild steel or stainless steel. steel. Fasteners: stainless steel Vapor Barrier: PTFE(Teflon). Leaf springs: Stainless steel Aromatic Resistance: 100%.
Wax Scraper: when storing waxy products, in accordance with the seals specification, VISTA would design a Wax Scrapper Device which could be easily installed at the lower sections of the compression Plates to prevent the accumulation and deposition of wax on the floating roof deck. Secondary Seal: VST – 21 is recommended as the secondary seal to all sealing solutions. However, all the other secondary seal devices including Shoe Mounted Secondary Seals can be supplied and installed.