mechanical seal

What is a split mechanical seal?

A mechanical seal is a device used to contain fluid within a vessel where a rotating shaft passes through housing, or sometimes where housing rotates around a shaft. These vessels are usually pumps, mixers, agitators, grinders, etc. The purpose of a mechanical seal is to allow the shaft to rotate freely without allowing large amounts of fluid to escape.

How is a split mechanical seal different from a component or cartridge seal?

A split seal comes in two separate pieces. Unlike ordinary cartridge mechanical seals, these two pieces can be installed or removed from around the shaft without disassembling the equipment. When joined, the sealing elements are mated to create a proper seal around the shaft.

When should a split mechanical seal be used?

The challenges facing process industries have changed although they continue to pump fluids, some hazardous or toxic. Safety and reliability are still of prime importance. However, operators increase speeds, pressures, flow rates and even the severity of the fluid characteristics (temperature, concentration, viscosity, etc.) while processing many batch operations. For the operators of petroleum refineries, gas processing facilities and petrochemical and chemical plants, safety means controlling and preventing loss of, or exposure to, the pumped fluids. Reliability means pumps that operate efficiently and economically, with less required maintenance.

A properly designed mechanical seal assures a pump operator of long-lasting, safe and reliable pump performance with a proven technology. Among multiple pieces of rotating equipment and a myriad of components, mechanical seals are proven to perform dependably under most types of operating conditions.

Pumps & Seals—A Good Fit

It is hard to believe that almost 30 years have passed since the mass promotion of sealless pump technology into the process industry. The new technology was promoted as the solution to all the issues and perceived limitations of mechanical seals. Some suggested that this alternative would eliminate the use of mechanical seals entirely.

However, not long after this promotion, end users learned that mechanical seals could meet or exceed legislated leakage and containment requirements. Further, pump manufacturers supported the technology by providing updated seal chambers to replace the old compression packing “stuffing boxes.”

Today’s seal chambers are designed specifically for mechanical seals, allowing for more robust technology in a cartridge platform, providing easier installation and creating an environment that allows the seals to function to their full potential.

Design Advancements

In the mid 1980s, new environmental regulations forced the industry not only to look at containment and emissions, but also at equipment reliability. The average mean time between repair (MTBR) for mechanical seals in a chemical plant was approximately 12 months. Today, the average MTBR is 30 months. Currently, the petroleum industry, subject to some of the most stringent emission levels, has an average MTBR of more than 60 months.

Mechanical seals maintained their reputation by demonstrating the ability to meet and even exceed the requirements of best available control technology (BACT). Further, they did so while remaining an economical and energy efficient technology available to meet emission and environmental regulations.

Computer programs allow seals to be modeled and prototyped prior to manufacturing to confirm how they will handle specific operating conditions before being installed in the field. Seal manufacturing design capabilities and the technology of seal face materials has progressed to the point that they can be developed for a one-to-one fit for a process application.

Today’s computer modeling programs and technology allow the use of 3-D design review, finite element analysis (FEA), computational fluid dynamics (CFD), rigid body analysis and thermal imaging diagnostic programs that were not readily available in the past or were too costly for frequent use with earlier 2-D drafting. These advancements in modeling techniques have added to the design reliability of mechanical seals.

These programs and technologies have led the way to the design of standard cartridge seals with much more robust components. These included the removal of springs and dynamic O-rings from the process fluid and made flexible stator technology the design of choice.

Consider mechanical seals, gland packed seals, and lip seals.

The drive for operational efficiency, optimization of assets, and adherence to the International Standards Organization (ISO) 14001 Standard for environmental management systems and ISO-50001 standard for energy management systems must always be balanced against the bottom line.

However, it is fair to say in some cases this can lead to short-sightedness when it comes to selecting sealing solutions, with lower cost at point-of-purchase taking precedence over total cost of ownership.

Mechanical seals have been on the market for around 80 years, and while pump design has remained largely unaltered, sealing technology has evolved over time. This has resulted in advances in reliability, operational efficiency, and environmental sustainability.

Traditional sealing options like gland packed seals and lip seals are traditional for a reason. These products are comparatively inexpensive when taking the purchase price into account, and work well in many applications. This article will take a look at the differences between mechanical seals, gland packed seals and lip seals.

Excessive Wear

Leakage, product loss and bearing contamination that leads to premature failure are three common issues with traditional seals.

There is no reason why bearings should not last for their full predicted lifespan, which is typically calculated at roughly 15,250 operational hours. Leakage caused by inefficient sealing is the simple reason why they do not last. With research showing that water contamination of just 0.002 percent—a single drop—in a bearings chamber can reduce bearing life by almost half, it is easy to see why bearing failure is one of the most frequent causes of pump malfunction. The cost of regularly replacing damaged seals and bearings accumulates over time and can escalate if the pump shaft suffers wear damage and must be repaired or replaced.

Another key cost, which is often overlooked, is the number of hours demanded to maintain, repair and replace these components.

Espey chamber seals have a modular design which means the seals can be composed using standard parts to meet individual application requirements. Espey chamber seals work with a very small operation gap between shaft and seal ring – leading to very low leakage – and are designed for dry-running and compensate radial and axial shaft deflections. Another advantage is that no sealing components which could generate additional shaft vibrations are actually fitted on the shaft. The seal rings are axially spring-loaded to prevent swinging up at pressure-less machine operation.

Espey chamber seals are applied in several turbo machines: integral gear, screw and chiller compressors, steam turbines, and shut-off valves for power plants. The main industries in which it is implemented are oil and gas, refining, chemical and petrochemical industry, power plants, and plants for iron and steel production. A further industry field with several references and successes is carbon dioxide

Mechanical Seals & API 682 4th Edition

A sealing system, consisting of a mechanical seal and an associated supply system that is balanced by individual applications, is the utmost guarantee for a reliable sealing point and uninterrupted pump service. The performance of the seal is greatly influenced by the environment around the seal faces, making the provision of suitable, clean fluids as well as a moderate temperature an essential topic.

This guiding booklet provides a condensed overview of all piping plans established by the API 682 4th edition guidelines. Each illustrated piping plan is briefly described, and a recommendation that considers the media characteristics in terms of the relevant application and corresponding configurations is given to help you reliably select your sealing system. Furthermore, the content of this booklet has been enriched by providing clues – so-called ‘remarks and checkpoints’ – where EagleBurgmann

Mechanical Seal SHVI and Plan 66A for Unmanned Pump Station of an Oil Pipeline

A well-known Canadian operator of an oil pipeline commissioned EagleBurgmann to develop a sealing solution for crude oil pumps. The requirement: It needed to be a single seal that was just as safe as a double seal with buffer pressure system. In addition, the sealing solution was not to be designed for only one pump type but should be installed in various pumps of one station.

The operating parameters were quite extensive: The seal needed to be suitable for a pressure range from 2.5 bar (36 PSI) to 99 bar (1,436 PSI) as well as for shaft diameters from 115 mm to 155 mm (4.53’’ to 6.10’’). Since the pump stations are operated unmanned, the seal must operate without