Full secondary seal, wiper type, for a floating roof tank

In a vertical cylindrical liquid storage tank of imprecise circularity having a circular floating roof of smaller diameter than the tank thereby defining a vapor space between the roof edge and the tank wall, an improved sealing means for substantially preventing flow of vapor from a liquid product stored in the tank through the vapor space to the atmosphere, said sealing means including:

• an elongated elastomeric composite strip, with parallel inner and outer edges, impermeable to vapor connected at its inner edge by an essentially vapor tight joint to the roof edge and extending as an annulus outwardly into contact with the tank inner side wall, said strip having uniformly smooth surfaces on both sides adjacent the outer edge,
• the elastomeric composite strip comprising a plurality of flexible resilient elongated stiffeners laterally positioned and embedded in elastomeric material,
• the elongated stiffeners extending from the strip edge joined to the roof and terminating short of the outer strip edge at the tank wall, and
• said elastomeric strip flexing in a vertical arc as the roof moves toward and away from any adjoining tank wall portion, with circumferential stretching and contraction of the strip at its outside periphery unrestrained by the stiffeners thereby permitting the strip to very readily and efficiently contact and accommodate to the contour and spacing of the tank wall from the roof edge to maintain sealing contact with the tank wall above the vapor space as the roof moves laterally and vertically and thus keep vapor from escaping.