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  • Specialised Seals and Flow Solutions


Viscous substances such as syrups, tars, thick oils, resins, and glues prove to be challenging for most mechanical seals. Lip seal designs have been the go-to option for these processes that have centipoise values well above the normal range for seal face operation. The Multi-Lip Cartridge Seal (MLC3) design by Flexaseal Engineered Seals and Systems, achieves optimum pumping rates at lower speeds with fewer sealing issues than products currently in the field and requires virtually no seal support system.The MLC3 is a modular triple lip seal arrangement designed to reliably handle a variety of harsh services. It is a versatile solution designed for use in common rotating equipment such as centrifugal pumps, positive displacement pumps, mixers, and agitators.

The operating principle of a multiple lip seal differs from a traditional mechanical seal in the way that the seal is formed. In an end-face mechanical seal, leakage is prevented via an axial load between a primary face which can be various grades of carbon, silicon or tungsten carbides and a mating face – typically a hard material such as silicon or tungsten carbide. An end-face seal operates on and is cooled by a micro-thin fluid film and can utilize hydraulic pressures to balance face loads for decreased heat generation and management of high pressures. These seals are extremely common across all industries and have been the standard solution for reliable sealing of rotating equipment for decades. In addition, many mechanical seal piping plans have been defined to provide leakage detection and monitoring of seal performance for both single and double mechanical seal configurations.

Multiple lip seals do not seal in an axial direction like their mechanical seal counterparts, but rather have a circumferential interference with the mating shaft/sleeve. The sealing arrangement is completely stationary aside from the rotating seal sleeve; this component is normally set and driven by the rotating shaft of the equipment. Multiple lip seals are especially suited for services that are highly viscous, slow-moving, and those that entail recurring start-ups or upset conditions. Some common media for triple lip seals include adhesives, paints, resins, and greases/oils, as well as common food products like syrups, molasses, and chocolate1. The Flexaseal MLC3 can handle viscosities up to 500,000 cP, pressures up to 300 psig, and surface speeds of 5,000 fpm with environmental controls or 3,000 fpm dry-running2.

The Flexaseal MLC3 cartridge seal design is helpful for ease in both installation and removal, as well as for installation on various equipment without a need to reconfigure the seal chamber’s dimensions. The radial squeeze of the lips allows them to operate independent of axial displacement; the MLC3 can handle up to 0.125” axial runout in its standard configuration. The TIR of .025” allowable radial run-out enables the standard MLC3 design solution to be applied in most suitable applications. The MLC3 triple lip seal arrangement provides the freedom to reconfigure the lips for a variety of service conditions, thereby allowing for the application of piping plans very similar to those employed with traditional double mechanical seals. In the conventional application, the lips are arranged to face the sealed media such that the seal chamber pressure increases the bending load on the seal element and circumferential squeeze on the rotating element. For vacuum service, the internal construction can be rearranged to maintain the pressure differential across the inboard lip in the energizing direction. The modular design allows for simple and consistent field service and repair.

The Style MLC3 utilizes a standard silicon carbide sleeve; a coated stainless steel sleeve option is also available. This sleeve design and material prevents the lips from wearing the shaft and any subsequent leakage caused by that wear. In addition, the hardened seal sleeve is an ideal surface on which the proprietary, filled PTFE-ML lips can operate. The MLC3’s specific engineered lip geometry combined with the PTFE-ML compound provide solutions for traditional elastomer lip seal issues by way of a lower coefficient of friction which leads to lower heat generation, as well as a nearly inert lip that is highly resistant to chemical attack. The enhanced lubricity of the PTFE-ML compound also allows for a higher pressure and speed rating (PV), which permits sustained dry running operation under certain conditions without degrading the lips or performance of the seal.

The versatility of the Flexaseal Style MLC3 creates a solution that can be readily applied in services across multiple industries.

Contact Specialised Seals and Flow Solutions to learn more.

1FDA-compliant materials of construction available upon request. 2Maximum ratings indicate operating extremes independently and does not imply the seal will function at these extremes at the same time. Reach out to the Specialised Seals and Flow Solutions Applications team ( for inquiries regarding specific operating parameters.


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