Process machinery often does not conform to sizing standards. Used in widely varying applications across a broad range of industries, the machines have unique dimensions and operating conditions tailored to diverse process requirements.

This presents a challenge during the selection of seals that prevent leakage of process materials from machinery. A single seal type and size will not be the ideal solution for every application. To ensure proper seal function, the seal’s specifications must be matched to the application.

In the case of rotating shafts entering a machine, mechanical seals serve as the interface between the shaft and machine, allowing smooth, low-friction motion while blocking any material from escaping the machine along the shaft and end wall.

MECO Seal, a manufacturer of custom-engineered mechanical seals, works closely with customers to design shaft seals that meet the unique requirements of their specific machinery and process parameters.

The MECO EP Type-1 shaft seal is optimized for applications involving wet abrasive slurries with medium-to-large diameter shafts in horizontal, vertical or inclined orientations. The EP Type-1 seal is ideal for industrial process applications such as the recycling and processing of pulp and paper, the manufacture of home building products, the treatment of sewage and water and the production of biomass and ethanol. The seal is well-suited for installation on pulpers, agitators, cylindrical blenders, paddle mixers, holding vessels, flocculators, mixing conveyors and other machinery in which a rotating shaft needs to be sealed where it passes through a vessel wall.

Operating principle

EP Type-1 seals are fully-split, which means that its 10 components are each divided into two halves. This design simplifies installation, eliminating the need to disassemble equipment. Each component of the seal is simply placed around the shaft and then joined together. Typically the two halves are secured by fasteners.

The design of EP Type-1 seals shares similarities to a stuffing box and gland follower. The rotary components of the seal consist of a drive elastomer sandwiched between two rotating seal faces to create a watertight seal with the shaft. The hardened rotating seal faces are lapped and polished to maximize performance. They press against the malleable material of the precision-machined stationary seal faces to form an effective, low-friction interface.

Figure 1: MECO EP Type-1 seal installed on a 415 mm shaft entering a pulper that is processing recycled office paper. Source: MECO SealFigure 1: MECO EP Type-1 seal installed on a 415 mm shaft entering a pulper that is processing recycled office paper. Source: MECO Seal

The two stationary seal faces consist of the inboard (or primary) stationary seal face and the outboard (or secondary) stationary seal face. The inboard seal face is built into a plate at the bottom of the seal housing, while the outboard seal face is formed by the nose of the gland follower. Sufficient force to align and press the seal faces closed is provided by springs attached to the external face of the gland follower.

Figure 2: Exploded view of the MECO EP Type-1 seal. Source: MECO SealFigure 2: Exploded view of the MECO EP Type-1 seal. Source: MECO Seal

Maintenance

A continuous flow of water enters and exits the cavity of the seal to perform three important functions. The water flushes out process debris to ensure a clean operating environment within the seal. It also serves as a heat transfer fluid, absorbing heat generated during the seal’s operation and transporting it away from the seal to keep the device within an acceptable operating temperature range. Lastly, the water acts as a diagnostic tool, helping verify proper seal calibration and assisting in predictive maintenance analysis through observation of the water’s clarity, change in temperature and leak-free passage through the seal cavity.

The stationary seal faces eventually wear by pressing against the rotating seal faces. As this process occurs, the external springs attached to the gland follower will expand to maintain contact between seal faces. The springs should occasionally be tightened to ensure maximum operating life for the seal. Eventually, wear of the seal faces will bring the gland follower flange into contact with the seal housing, requiring a rebuild of the seal. This may be accomplished on site or at MECO’s factory.

Construction

MECO EP Type-1 seals are engineered for long operational life and constructed with high-quality, rugged materials. The materials of construction for EP Type-1 seals are broadly customizable; MECO Seal can accommodate any specific material requests for unique applications. Common material choices are listed below.

The rotating seal faces are fabricated from hardened stainless steel, while the housings and gland follower are made out of 304 or 316 stainless steel.

Figure 3: MECO EP Type-1 seal installed on a 300 mm shaft entering the bottom of a high-consistency pulper. The inlet and outlet water flush lines are visible on the left and right sides of the seal. Source: MECO SealFigure 3: MECO EP Type-1 seal installed on a 300 mm shaft entering the bottom of a high-consistency pulper. The inlet and outlet water flush lines are visible on the left and right sides of the seal. Source: MECO Seal

Typical options used for the stationary seal faces include the following high-performance, bearing-grade materials.

  • MECO 3000: a slippery, polymer-filled polytetrafluoroethylene (PTFE)
  • MECO 3120: a malleable, ceramic-filled PTFE
  • MECO 4000: a hard, carbon fiber, graphite and PTFE-filled polyetheretherketone (PEEK).

For elastomer materials, ethylene propylene diene monomer (EPDM) is a common choice. White silicone, Viton and nitrile rubber are other possibilities. FDA-compliant options are also available for these materials.

Figure 4: Typical dimensions for a MECO EP Type-1 seal. Source: MECO SealFigure 4: Typical dimensions for a MECO EP Type-1 seal. Source: MECO Seal

Specifications

MECO EP Type-1 seals are custom designed and built to meet the specific operating conditions and the dimensional needs of widely varying types of process equipment. The seals are typically used on shaft diameters ranging from 4” (100 mm) to 16.5” (420 mm), although sizes outside of this range can be accommodated. Optimal axial clearance for ease-of-installation is 12” (300 mm), although a clearance of just 6.5” (165 mm) is feasible. A minimum shaft protrusion of 3” (76 mm) is required, with 5” (127 mm) desired.

The typical mounting bolt circle diameter is the shaft diameter plus 3.5” (90 mm). The total outside diameter of the seal is typically the shaft diameter plus 6” (150 mm).

Figure 5: Mechanical capabilities of the MECO EP Type-1 seal. Source: MECO SealFigure 5: Mechanical capabilities of the MECO EP Type-1 seal. Source: MECO Seal

Conclusion

MECO EP Type-1 seals are the best option for sealing wet, abrasive slurries in a wide range of rotating process equipment. The ideal choice for both retrofits and new equipment, the seal’s fully-split assembly eases installation, its precision-machined components prevent leakage and its water flush design clears out process debris, removes heat and ensures reliable seal operation and predictable maintenance.

Contact MECO Seal today through their website or by phone at 1-800-526-8800 for assistance with engineering the perfect seal for your process.