A Spotlight on MECO EA Type-1 SealsDecember 11, 2018
Meeting the highly specific needs of process manufacturing often requires semi-customized seals that are engineered and designed for fit and function for a particular application and the specific original equipment manufacturer’s (OEM) sizing standards. Custom-engineered shaft seals from MECO Seal eliminate many common problems with respect to performance (tolerating 0.25 inch and more of diametric runout), safety (no braided packing to pull out of the stuffing box), productivity (fully split installation) and harmony (less physical strain on personnel). MECO can also help train maintenance staff on seal maintenance, repair and overhaul (MRO).
Wet slurry environments present a unique sealing challenge. Typically, slurry particles continually attack any sealing interface, resulting in destructive wear near or at this interface. Minor upsets related to stopping and starting, emptying, and loading of the slurry components and their changing viscosities all place non-steady-state operating conditions on the equipment and seals. These change-of-state conditions commonly introduce hard slurry particulates into the sealing interface or the softer particles fracture into smaller, jagged particles that tenaciously invade openings as they gradually seep into the dynamic interface, wearing all the components they touch.
A slurry seal often employs a water flush, water quench, water purge or continual greasing to help survive the harsh environment. All are prone to clogging, causing excess heat generation and positive pressure in the seal cavity. Additionally, purging or pressurizing the seal cavity risks diluting the process with water. Greasing the seal cavity provides a collection medium for wearing particles to gather, eventually accelerating the wear rates and the number of parts wearing. Proper controls and understanding of their functions are important.
The MECO EA Type-1 is a fully split seal that facilitates easy installation and maintenance. This model addresses the issues associated with sealing in wet slurry conditions. To resist scoring, the EA Type-1 features two hardened, stainless steel seal faces that rotate against two stationary, bearing-grade, polymeric seal faces. The plane of the seal faces is perpendicular to the shaft axis and uses an elastomer drive. The split polymeric seal faces mount on two fully split stainless steel plates. During installation, one split plate is mounted on the vessel wall while the other is positioned a specific distance from the mounted plate, separated by an elastomer, which creates the seal cavity. Very low pressure or gravity-fed water flushes out the bottom of the seal, removes invading particles and cools the seal cavity’s sliding interfaces without applying backpressure or risking dilution. Discharge plumbing is very short, directed downward without any traps, horizontal runs or flow restrictions, and is positioned for easy inspection.
How Does the MECO EA Type-1 Seal Model Work?
The EA Type-1 mechanical seal consists of two main components: a rotating member and a stationary member. The rotating member consists of the driving elastomer and two stainless steel seal faces. The elastomer is located on the surface of the shaft between and interlocked with the two stainless steel seal faces. The elastomer provides two key functions. It creates a watertight seal while it turns or “drives” the two seal faces, or “rotors,” as the shaft rotates.
The second main component is the stationary member, consisting of an inboard and outboard housing that contains the two self-lubricating, stationary polymeric seal faces, or stators. The inboard and outboard housings are bolted together to form the stationary part of the seal. An adjusting gasket between the inboard and outboard housings forms a seal cavity between the two housings for containing the flush and quench water.
The rotor and stator seal faces are mounted perpendicular to the shaft axis and operate without boundary lubrication. A water flush removes debris from within the seal cavity, cools the hardened stainless steel faces and assists in determining when to make an adjustment.
How is the MECO EA Type-1 Seal Model Maintained?
Walk-by inspections or remote flow sensors help ensure that the seal is in good operating condition to maximize the mean-time-to-repair (MTR) and minimize costly downtime. Flush water becomes cloudy over time, indicating that the seal may require an adjustment or that a pressure surge occurred. Seal adjustment is possible without emptying or disassembling the vessel. However, performing adjustments prior to leaking is important. When an adjustment is required, simply reduce the distance between the housings by an incremental amount.
Additional items can and should be inspected routinely. Excessive temperature increases between the flush water inlet and outlet indicate a problem. To check the calibration, the seal should contain low backpressure restrictions for a 20 to 30 second timeframe. A few drips are permissible, but a stream indicates that it is time for an adjustment. A seal that can no longer contain flush water or product requires a rebuild. Rebuilding entails removing the seal and replacing the hardened seal faces, the polymeric sealing faces and elastomer elements. Seal rebuilding on site is typical. Often, the hardened seal faces may be reconditioned.
What Construction is Available?
All MECO EA Type-1 seal components are designed for durability and long life. Several standard material options are available and custom material solutions are workable.
The standard assembly uses hardened stainless steel rotating seal faces with housings machined from 304 or 316 stainless steel. Several bearing-grade, stationary seal face materials are available. Selection of the appropriate material depends on the operating environment and application. Common high-performance bearing-grade stationary seal face options are as follows:
· MECO 3000, a slick, polymer-filled PTFE
· MECO 3120, a malleable, ceramic-filled PTFE
· MECO 4000, a hard carbon fiber, graphite and PTFE-filled PEEK
Several elastomer material options are available as well, including EPDM (the most common elastomer), white silicone, Viton® and nitrile. FDA-compliant options are available.
What Sizing is Available?
All MECO EA Type-1 seals are built to order. Common shaft diameters range from 4 in (100 mm) to 16.5 in (420 mm), in addition to many sizes outside of this range. Although typical dimensions are available, each seal is designed to fit the application. Seals can be built with either SAE or metric fasteners. Typically, all EA Type-1 seals are fully split for easier assembly and maintenance.
When Are EA-Type 1 Seals the Best Option?
The MECO EA Type-1 seal model is ideal for sealing wet, abrasive slurries in rotating equipment such as pulpers, agitators, cylindrical blenders, paddle mixers, holding vessels, flocculators and mixing conveyors with limited axial or linear space. EA Type-1 seals are used in industries that require processes handling water slurries: pulp and paper, home building products, sewage and water treatment, biomass, and ethanol production, to name a few. These seals are well-suited for side-entry mixers containing drywall or sheetrock mud. Customization and enhanced features make these seals easier and safer to maintain.
Pulpers that recycle office paper and old corrugated containers (OCC) benefit from EA Type-1 seals’ ability to withstand shock loading, high shaft runout and abrasives. The entire assembly is fully split and serviceable onsite.
To begin collaboration on the custom solution for your applications, visit MECO or call 1-800-526-8800.