mechanical seals
- July 21, 2025
Elastomer Technology in Mechanical Seals
Evaluate properties of rubber during installation and seal life.
Elastomers (or rubbers) are a ubiquitous family of materials whose use stretches across nearly the entire range of mechanical seal designs. From plant-sourced natural rubber, so named by John Priestly in 1770 for its utility in rubbing away pencil graphite, to petroleum-sourced synthetic rubber first developed around the turn of the 20th century, the "elastomer" and their properties are familiar but should not be overlooked—especially when dealing with mechanical seals.
How Elastomers Work in Mechanical Seals
Rubber seals come in a variety of profiles—O-rings, cup gaskets, bellows diaphragms, sealing/wiper lips and many others. They are classified as either static or dynamic and create positive pressure against surfaces to eliminate or control the leakage of liquids and/or gases while preventing the entrance of external contaminants such as dust and dirt. Static sealing occurs between adjacent surfaces with no relative motion, such as between the pump casing and cover. Due to frictional wear and heat generation, dynamic sealing is less straightforward, occurring between adjacent surfaces that are continuously or intermittently moving relative to another, such as between the pump casing and shaft.
In mechanical face seals, elastomers tend to take second chair because the primary seal—the dynamic seal between the housing and rotating shaft—is achieved by sliding contact between the pair of stiffer, lapped-flat sealing faces, one stationary in the housing and one rotating with the shaft. In many designs, rubber provides the secondary seal between each seal face and adjacent surface. One seal face is fixed and sealed statically using an O-ring or cup gasket. The other is spring-loaded and requires a semi-dynamic seal to accommodate some axial play, such as a dynamic O-ring in pusher-type mechanical face seals or elastomeric bellows in nonpusher ones. These semi-dynamic applications (involving flexing and sliding of the elastomer) can be critical for maintaining proper contact between the faces through face wear, shaft movement, etc.
Common Applications
Although the seal face pair tends to be the most critical design feature, mechanical face seals are often used in the most demanding applications.
Rubber technology features prominently in radial lip seals, where typical applications have lower pressurevelocity (PV) values relative to those involving mechanical face seals. Still, the flexible elastomer lip must handle considerable relative motion in the form of shaft/bore rotation, reciprocation or a combination of both. In addition to standard designs and sizes, numerous customizations and proprietary approaches exist. The simplest designs rely on a single rubber lip’s inherent resiliency, although common enhancements include multiple sealing lips, a circumferential garter spring installed in a groove over the sealing lip to maintain contact with the shaft, and an auxiliary wiper lip or “excluder” to prevent abrasive dust or debris from compromising the primary sealing surface. For improving service life and performance in rotary applications, unidirectional or bidirectional hydrodynamic pumping aids can be added in the form of custom-shaped extrusions on the backside of the sealing lip to return leaked fluid to the sealing interface, increase lip lubrication and lower operating temperatures.
Benefits of Rubber
The definition of an elastomer provides initial insight into where rubber gets its resilient sealing quality: “a macromolecular material which, in the vulcanized state and at room temperature, can be stretched repeatedly to at least twice its original length and which, upon release of the stress, will immediately return to approximately its original length.”
When the rubber is squeezed by the adjacent surfaces of the clearance gap to be sealed, it has the characteristic
properties of malleably deforming and taking the shape of each surface in response to the stress and applying a force back against the surfaces in its attempt to return to its original dimensions. Elastomers consist of large molecules called polymers (from the Greek “poly” meaning “many” and “meros” meaning “parts”), which are long chains of the same or different repeating units, called monomers, usually linked together by carbon-carbon bonds (the
most notable exception being silicone elastomers, which are linked by silicon-oxygen bonds). Soft and hard plastics are also composed of polymers. However, the regularity of the monomers in their polymer chains allows neighboring segments to align and form crystals, making the macromolecular plastic material rigid and inelastic.One can prevent this crystallization by breaking up the regularity of the polymer chain, resulting usually in a viscous “gum” that is readily shaped into molds. At the molecular level, the polymer chains are similar to spaghetti-like strands flowing past each other.
During the process of vulcanization, or curing, the viscous liquid is heated with sulfur or peroxides and other vulcanizing agents, and crosslinks form between polymer chains, tying them together with chemical bonds, converting the gum into an elastic, thermoset solid rubber that retains its shape after moderate deformation.
In addition to the selection and preparation of base polymer(s) and cure system ingredients, formulating the final rubber product, also known as compounding, involves five other broad categories of ingredients, which have percentage compositions expressed in parts per hundred rubber (phr). Fillers include various powders that thicken the polymer mixture, improve strength and resistance to abrasives, and reduce final cost. Plasticizers are oils and other liquid hydrocarbons that lower viscosity to ease processing, soften the final compound and in some cases improve low temperature performance. Process aids are specialized chemicals added in low concentrations to improve mixing, flow properties and final appearance.
Antidegradants protect the rubber from environmental attack. Finally, various miscellaneous ingredients may be added for special purposes, including foaming agents, dyes, fungicides, flame
retardants, abrasives, lubricants and electrically conductive particles. A simplified description of processing these ingredients includes mixing via tangential or intermeshing mixers, forming into desired shapes and vulcanizing into the final product. - October 04, 2022
- September 10, 2021
Pumps are essential throughout the world. They are used to move all types of liquids in a wide variety of applications. Examples of industries where pumps are used are: Chemical & Pharmaceutical, Oil & Gas, Pulp & Paper, Power Generation, Water & Wastewater, Food & Beverage, Cosmetics, General Industrial, and much more.
Pump Seals and Mechanical Seals for Pumps
Seals are an integral part of any rotating equipment handling fluids. There are a wide
- October 27, 2020
What is a split mechanical seal?
Splitex - A split seal by EagleBurgmann 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?
- November 29, 2019
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.
- November 12, 2019
Springs are an integral part of all sealing systems. A simple air cylinder has O-rings to seal in the air, and the O-ring exhibits spring-like qualities to ensure a good seal over a broad temperature range.
But what are the different types of springs and materials in sealing systems? And how do you choose the best for your application?
- July 22, 2019
What is DiamondFace Technology?
DiamondFace is an innovative microcrystalline diamond coating for mechanical seals. It is extremely hard and offers high wear protection, excellent heat conductivity, maximum chemical resistance and low friction. The coating adhesion also exceeds all known practical requirements. This increases the service life of mechanical seals several times over, the maintenance intervals are extended accordingly and the life cycle costs are greatly reduced.
The diamond thin-layer technology was developed in 2007 by EagleBurgmann together with the Fraunhofer Institute for Surface Engineering and Thin Films (IST), the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS), Fraunhofer Institute for Mechanics of Materials (IWM), the Condias GmbH, and the Forschungszentrum Jülich. EagleBurgmann has established DiamondFace for mechanical seals as a series-produced product - the very first on the market.
The technology behind it is a microcrystalline diamond layer up to 15 μm thick which is applied to the seal face under vacuum at temperatures of 2,000 °C (3,632 °F) by chemical vapor deposition (CVD). The properties of this diamond layer are where you benefit. Primarily from its extreme hardness and robustness.
Increased Service Life of Mechanical Seals
Mechanical seals are a factor that has a decisive effect on the cost-effectiveness of your operation because their wear determines the productivity of the entire system, whether it is a pump, agitator or compressor. What causes damage to the seal faces? One reason is dry running which is often unavoidable due to insufficient lubrication or when gas-lubricated seal faces get in contact. The resulting temperature rise causes the seal to wear. And ultimately results in system downtimes.EagleBurgmann has solved this problem which directly affects the success of your plant. Thanks to DiamondFace, the service life of mechanical seals is increased several times over, the maintenance intervals are extended accordingly and the life cycle costs are greatly reduced. The advantages for the operator are clear:
- July 08, 2019
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.
- June 10, 2019
Innovation in Detail: eMG and eMG1
With the latest generation of pump seals, eMG1 and eMG, EagleBurgmann has launched
- May 23, 2019
Mechanical sealing conserves water, improves energy efficiency, and minimizes environmental impact
The environmental performance of products and processes in all industrial sectors increasingly is cause for critical inspection, with sustainability, conservation of natural resources, and reduced environmental contamination concerns influencing equipment design and selection.
Many industrial processes can be addressed to improve sustainability and minimize environmental impact, while at the same time maintaining or reducing operating costs. Implementing energy-efficient and environmentally friendly processes and technologies should be embraced as a priority at the component, process, and system levels.
One aspect of these processes is mission-critical rotating equipment, and specifically centrifugal pumps, which represent a significant proportion of the equipment found in industrial operations. One vital component of a centrifugal pump is the seal around the rotating shaft that passes through a stationary pressure casing or housing. The seal contains the liquid or gas from escaping to the environment.
Sealing systems help maintain acceptable pump efficiency, reliability, energy consumption, water usage, and emissions control. These factors can materially facilitate achieving total-life cycle cost-reduction and sustainability objectives. Sealing performance can be improved for centrifugal pump applications by upgrading from traditional compression packing to mechanical seal technology.
When sealing a centrifugal pump, the objective is to allow the rotating shaft to enter the wet area of the pump without large volumes of pressurized fluid escaping. The pump discharge pressure forces the fluid back behind the impeller, where it is induced to exit by way of the rotating drive shaft. To minimize leakage, a seal is needed between the shaft and pump housing to contain the pressure of the process being pumped and withstand friction caused by shaft rotation.
Compression packing is the traditional means to seal centrifugal pumps, going back more than 100 years. Also referred to as gland packing, it is a braided, rope-like, and lubricated material packed around the shaft in rings, physically stuffing the gap between the shaft and the pump housing, within a stuffing box.
Water leakage and consumption
For compression packing to work, some leakage must be maintained to lubricate and cool the packing material. Therefore, packing rings allow for an adjustable, close-clearance leak path parallel to the shaft axis. As the packing is used, however, some of the lubricant that is embedded into the packing is lost, reducing the packing ring’s volume. The pressure squeezing the rings together is also reduced, increasing leakage.
Periodic adjustment of the packing follower brings the pressure back into specification and controls the excess leakage. In today’s world, however, this maintenance is not always being done at required intervals or adjusted correctly. As the number of centrifugal pumps incorporating the use of compression packing decreases, training for and understanding of packing maintenance has waned.
Consequently, under-tightening and over-tightening of packing rings is a prevalent and growing misapplication of centrifugal pump maintenance, with critical consequences to both water consumption and energy draw.
Under-tightening results in too much leakage. Already, when properly adjusted, packing leakage can amount to gallons of liquid leaked per minute. This can be either aqueous solutions comprised of varied benign or caustic chemical compositions, or particles in suspension or slurry, depending on the process.
The heavier the suspension or slurry content in the pumped liquid, the more water is needed to get packing to work reliably. Typically, a clean external flush is piped into the stuffing box through a lantern ring, which keeps the packing lubricated and cool while flushing abrasives and chemicals.
Normally, some portion of the leakage is released continually into the atmosphere. Under-tightening of the packing rings and use of external flushes increase this atmospheric release proportionately, along with environmental impact potential.
