Machine Design

Change seals without stopping equipment

Externally adjustable seals can be installed and rebuilt while equipment is still running.

Externally adjustable seals (EAS) keep powders, pastes, fluids, vapors, and gases from escaping a variety of rotating equipment. Traditional packings usually fail in such equipment. The seals are manufactured fully split, so they can be installed and rebuilt without removing bearings or the drive.

Seal face pressures are fully adjustable, so there are no internal springs to loosen due to seal face wear, or to corrode in hostile environments. All adjustment hardware is outside the seal's purge cavity, so seals can be adjusted without disassembly, often while the equipment is operating.

The seal incorporates separate inboard and outboard stator housings, which come together to compress two seal rotors against a central driving elastomer. The elastomer pressures the seal faces and grips the circumference of the shaft. As the driving elastomer rotates with the shaft, the two seal rotors turn with it.

A circle of adjusting studs connects the two housings, which contain the inboard and outboard stator surfaces. The inboard stator housing, with adjusting studs, is bolted flat against the machinery bulkhead or stuffing box. Nuts on the ends of the adjusting studs control the gap between the stator housings, controlling the internal seal face pressure. A special gage is furnished for measuring this gap.

Two seals are formed at the interfaces of the rotors and stators. The driving elastomer's tight grip against the shaft prohibits material from leaking along the length of the shaft. An adjusting gasket lets the gap between the two stator housings change, while still containing a purge medium within the seal. The seal can be purged with air, inert gas, or fluids, depending on the process involved.

The EAS and stator housings can use various materials to withstand a wide range of physical and chemical environments. Stators and rotors are stainless steel or bearing plastics. Seals can be made that withstand process temperatures of up to 500°F.

The EAS is custom-designed for each application but normally incorporates 1/4 in. of total runout/misalignment capacity. Where needed, more runout capacity can usually be provided.

Although originally designed for paper pulps, the EAS is now in service on a variety of equipment in the chemical, plastics, food, pharmaceutical, and biotechnology industries.

The EAS can be used on applications with speeds from less than one to 3600 rpm. The company also makes fan and blower seals for safe, reliable containment of hazardous fumes and gases.

This information provided by MECO Systems.

TAGS: Hydraulics
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