Storage Tank Foam Seal

Resilient toroids are the best fit for vapour mounted service because if a small tear or puncture occurs, the seal can continue to function. If the seal is liquid-mounted, the envelope quickly fills with product and either destroys the inner material or causes the seal to lose its shape and expansivity. However, they are used in both vapor and liquid mounted applications. Resilient toroids have a typical life of only 5 to 7 years compared to at least 20 to 30 years for mechanical shoe seals, but the installed cost is much less. Resilient toroid seals have very few mechanical hardware components to corrode or wear away. However, the toroid materials tend to wear fast and puncture easily as the roof moves up and down.

Liquid mounted (primary only): Mechanical Shoe - rugged, long-lasting, most costly, details of attachment important for long life, tends to wear away internal shell coatings faster than other seal types, can attach wax scrapers.

Liquid or vapour mounted (primary or secondary): Resilient Toroid (liquid or foam) - good seal, low cost, subject to tearing on rough surfaces, deflates when torn, poor in liquid-mounted service, material compatibility critical for long life, main failure mode is wear of outer protective cover, cannot attach scrapers.

Vapour mounted (primary only for internal roofs, secondary): Flexible wiper - low cost, good seal, conforms to shell irregularities, best designs use compressor plates and vapor barrier fabrics, material and trim selection important, wiper tip subjuct to wear, subject to approval by air agency.