Mechanical seals are found on most rotating equipment such as pumps and mixers to prevent the leakage of liquids and gases from escaping into the environment. The pump, therefore, is only part of the system – and its performance and reliability is directly linked to that of the seal. A mechanical seal consists of two principle components. One component is stationary and the other rotates against it to achieve a seal. There are many types of mechanical seal, ranging from simple single spring component designs to considerably more complex cartridge seal types. The design, arrangement and materials of construction are essentially determined by the pressure, temperature, speed of rotation and product being sealed.
The component seal ranges available today incorporate seals to suit an extensive range of pump types and applications in industries ranging from wastewater through to food and beverage, chemical processing to automotive. These seals are used in large volumes and, as the name suggests, are supplied as separate rotary and stationary assemblies for installation on site. This kind of seal is classified as a consumable as they are relatively low cost and repairing or replacing individual components is not usually economical. Of course, operating the seal in optimum conditions will ensure a longer life.
Component seals consist of multiple parts including rotor, rotor face, stationary face, springs, O-rings, gaskets and seal gland. Each of these needs careful handling and considerable care and skill during installation. As a result, component seals incur greater potential for assembly errors, for example, incorrect spring setting (resulting in improperly loaded faces), dirt or grease contamination on sealing faces and damage to sealing components due to mishandling. All of these have the potential to result in premature, or immediate, failure of the seal.
One of the major limitations with component seals historically, therefore, is that they were time consuming to install. Another consideration was that if conditions on site were not ideal or there was added time pressure to get equipment up and running it may have resulted in any one of these factors further compromising the seal’s performance.
Build to Order
The variety of material combinations, size and product variants can lead to a large amount of stock being needed to offer customers the seal that they require.
In order to streamline our business and improve the quality of component seal product we could offer we took the decision to re-engineer our component seal range to increase modularity and raise the industry standard, allowing configurable component seals to be built to order. Although it sounds a relatively straightforward project, in reality it involved a multi-million pound investment programme over four years. However, we achieved what we set out to do and are confident that the patented features are a game changer in terms of improved pump reliability.
Incorporating a build to order philosophy, the range offers a larger selection of product variants, and standard product lines can be easily adapted. Because of the sheer number of pumps and mixers that require component seals, the range comprises over 10,000 product lines available from stock and over 44,000 product permutations configurable. Advances in modularity enable customers to benefit from faster order processing and a significant reduction in lead times.
Bridging the component – cartridge gap
As part of the process we adapted cartridge seal technology into our component seals to include features that overcome limitations in competitor products, for example; improved seal face cooling through directed barrier fluid flow systems, hydraulically balanced seal face technology and ‘plug in’ designs to improve performance and reliability.
This ‘plug-in’ design fills a gap between component seals and cartridge seals as they don’t require setting and so have a reduced fitting time and ensure correct installation. This is a major step forward in terms of component seals and brings them closer to that of a cartridge seal.
Product Upgrade alternatives – helping to improve reliability
In our P0-U range we have developed an Axially Restrained Drive Ring, which is another way of aiding seal installation as it stops the drive ring from becoming detached from the retainer on installation. In addition, a full convoluted diaphragm allows for more axial movement of the rotary face than the half-convolution bellows. This enables the seal rotary to track the stationary much better in the event of misalignment of the two faces (due to seat incorrect positioning, shaft misalignment etc). The full convolution bellows can also compensate for more wear of the rotary face and handle higher pressures than the half-convolution bellows.
A common failure mode in seals of this type is the drive mechanism between two relatively thin metallic members. To overcome this problem, we have spread the drive force over a large surface area. The resulting patented design incorporates over 250% additional drive area compared to some seals found in the market place. This reduces the possibility of seal face hang-up and/or premature seal failure.
A further design improvement to the ‘plug in seals’ is Directed Barrier Fluid Flow, which again directly improves seal performance and life.
In order for seal faces to have as long life as possible they require optimum running conditions. This means they require clean fluid to pass between the faces. Due to the friction between the two faces heat is also generated. If this heat builds, the faces distort or the product evaporates reducing the fluid film and so more friction occurs. Eventually the faces will generate excessive heat and so contact will occur and the seal will fail. Directed barrier fluid means that clean, cool fluid is passed around the faces ensuring that heat generation is reduced and excessive friction between the faces does not occur. This overall increases the seal face life.
It is worth bearing in mind that component seals are typically unbalanced, which means that all the product pressure acts to close the gap between the seal faces and cause face contact. This is the reason why we incorporated Hydraulically Balanced Seal Design features into many of the upgraded products. Commonly used in our cartridge seals, balanced seal design means that the product pressure acts over a thinner area than the seal face running track area and so reduces the closing force. This allows the seals to operate in higher pressures and at higher shaft speeds, generating less heat and face wear. Overall, balanced seal faces will have a longer operating life than unbalanced seals – whether they are component or cartridge seals.
For specialist applications, and in addition to the standard elastomers such as EPR, Viton® and Nitrile, we offer AES-ELAST™. This combines the excellent thermal resistance of Viton® with the unique resistance to chemicals and environments that have historically exceeded the performance of conventional fluoroelastomers, particularly in highly caustic and steam applications.
New improved supply chain
Re-engineering our component seal range gave us an opportunity to look at how we manufacture these volume items. In order to control quality better we now manufacture the majority of the product in house and one of the benefits of this is that it allows us to provide food safe products backed up with appropriate certifications.
F- seals for the food and beverage industry are manufactured in accordance with Good Manufacturing Practice (GMP) which assures compliance with EC2023/2006 and is third party audited to ISO9001. Our materials are traceable in accordance with EC1935/2004 article 17 and our stock control systems are third party audited to ISO9001. In our F- seals we supply Food and Drug Administration (FDA) & EU Directive 1935/2004 compliant product wetted materials as standard to ensure our customer’s site comply. More importantly we can trace the components that the seal were built from back through the supply chain.
Summary
In re-engineering our component seal range we have extended product availability, quality assurance, and service. This has raised the industry standard and allows configurable component seals to be built to order. Technology upgrades that offer a ‘plug in’ type solution now fills a gap between component seals and cartridge seal technology.
Until now few companies have been prepared to invest this amount of time and resource into developing the next generation of component seals. However, we felt that it was important because the volume side of the market remains dominated by component seals. The result is that we now have the same modular build-to-order business model in our component seal range as our cartridge seals – and that is a major step forward.
All companies know that investing multi-million pounds in re-engineering an existing product range means that it must provide customers with an element of difference. When this is combined with a better control of the supply chain and improvements in reliability, it has the ability to change the game within the component seal sector.”
