Selecting the right seals for your process is as fundamental as selecting the right pumps, valves or mixers — all of which, of course, rely on sealing technologies for their efficient and environmentally sound operation. Indeed, as pressure rises on plants to improve productivity and equipment reliability levels, seals and gaskets are being called upon to provide even better performance. Their challenge no longer is simply to prevent leaks but also to play an important role in the life-cycle management of the plant.
Scott Boyson, global business development manager for sealing specialist A. W. Chesterton, Wakefield, Mass., sums up that role as “understanding how to integrate your product with the plant and add value.”
He says customers in the chemical industry are focusing more and more on the reliability of the entire plant, “not just your product.” At the same time, “they are looking for more support from their suppliers in the areas of technical expertise and know-how specific to their plant — not just specific to your product,” he adds. Plant operators now are concerned more with the performance and reliability figures of “asset classes” — the entirety of valves or pumps in a plant, for instance, rather than of an individual item of equipment.
Seal suppliers dealing with multiple customers are in a good position to offer sound advice on what are the best practices to adopt for these asset classes, says Boyson. A similar point is made by Tom Bennett, product manager with Flowserve in Dallas, Texas. “We can suggest better ways of running equipment to improve mean time between repair, seal life and so on,” he says, adding that the customer might not necessarily want to run its plant in that way, though.
With so many plants now being pushed to their operating limits to boost productivity, Bennett notes that many customers simply say: “This is how we’re going to run our equipment — you make it run longer.”
The consequence of such customer demands on all seal suppliers has been a constant upgrading of seal and gasket designs.
Around the middle of last year, for example, Flowserve launched the GCX single mechanical cartridge seal for ANSI/DIN chemical pump applications on multiple process fluids (Figure 1).
Instead of the elastomeric components used in other seals, the GCX features flexible graphite-foil secondary seals to handle the often-aggressive nature of multiple chemical environments. Batch processing and intermediate chemical pumps also often handle multiple-pH-level products as the process progresses, during which time there is no opportunity to change out the secondary seal. “Because it works across applications, the GCX allows plant managers to standardize inventory and reduce costs,” notes Mark Fallek, Flowserve’s vice president of marketing.
“Chemical compatibility has always been an issue,” says Bennett, noting that for seal face materials — the “tribological pair” — incremental increases in compatibility are arising from the use of techniques such as diamond coatings and some different silicon combinations. “We use diamond coating on compressor seals and have tried it on some of our standard seals and engineered seals,” he says, “but the cost effectiveness isn’t really there for ANSI- and DIN-type pump seals.”
John Crane, Morton Grove, Ill. and Slough, U.K., also is investigating the use of diamond coatings. The company has had a long-running collaboration with Advanced Diamond Technologies (ADT), Romeoville, Ill., to develop and commercialize ultrananocrystalline diamond (UNCD) as a means to improve the friction and wear characteristics of mechanical seal faces. (UNCD is the trade name for thin-film diamond material grown through a patented chemical vapor deposition process developed at Argonne National Laboratory, Argonne, Ill., and licensed by ADT in 2004.) “We are now looking at lead users and doing some work in the field with interesting applications,” notes Rick Page, vice president of marketing for John Crane Americas.That ongoing development project is one for the future, but Page sees immediate impact for three new product lines the company recently introduced.
The 7800 Series is a range of heavy-duty universal vessel seals for a wide variety of mixers and agitators. “Actually,” says Page, “the 7800 is a platform for four different seal arrangements. You have the same modular hardware so you can convert from one to another after you have bought the initial set.”
Within that platform, the Type 7828G gas-lubricated double seal uses dry nitrogen as a barrier gas and John Crane’s patented spiral groove technology to separate the primary seal faces. For duties requiring reduced barrier-gas consumption, the hybrid 7828GD offers a combination of non-contacting faces inboard and dry contacting faces on the outboard seal — but still in the same hardware as the 7828G. Similarly, the Type 7848D and Type 7848W use identical hardware while offering, respectively, proprietary face materials to run in a dry nitrogen barrier with virtually no wear, and a conventional liquid lubricated seal intended as an alternative to running dry and non-contacting.
A common operating problem encountered with many single outside-mounted dry-running mixer seals is audible running noise or seal face squeal — a problem John Crane is addressing with the launch of the Type 32i seal (Figure 2).
The primary ring of this dry-running top-entry mixer seal attenuates the generation of a vibration signal associated with dynamic face contact squealing. The result is a continuously self-adjusting interruption in resonance and quiet operation, making the seal particularly suited to interior plants typical of the pharmaceutical and fine chemical industries that have to meet OSHA workplace noise regulations.